From 8f3fe9cd028592b4b1449c2a5e6dba482bed0549 Mon Sep 17 00:00:00 2001
From: Roman Leventov <leventov.ru@gmail.com>
Date: Thu, 15 Nov 2018 22:21:34 +0100
Subject: [PATCH] Prohibit String.replace() and String.replaceAll(), fix and
 prohibit some toString()-related redundancies (#6607)

* Prohibit String.replace() and String.replaceAll(), fix and prohibit some toString()-related redundancies

* Fix bug

* Replace checkstyle regexp with IntelliJ inspection
---
 .idea/inspectionProfiles/Druid.xml            |  8 ++
 .../DimensionPredicateFilterBenchmark.java    |  2 +-
 ...loatCompressionBenchmarkFileGenerator.java |  2 +-
 ...LongCompressionBenchmarkFileGenerator.java |  2 +-
 .../benchmark/BenchmarkDataGeneratorTest.java |  2 +-
 codestyle/druid-forbidden-apis.txt            |  5 +
 .../druid/java/util/common/StringUtils.java   | 91 +++++++++++++++----
 .../common/granularity/PeriodGranularity.java |  6 +-
 .../emitter/core/ParametrizedUriEmitter.java  |  3 +-
 .../core/ParametrizedUriExtractor.java        |  2 +-
 .../java/org/apache/druid/math/expr/Expr.java |  4 +-
 .../org/apache/druid/math/expr/Function.java  |  8 +-
 .../druid/common/utils/UUIDUtilsTest.java     |  3 +-
 .../java/util/common/StringUtilsTest.java     | 25 ++++-
 .../core/ParametrizedUriEmitterTest.java      |  2 +-
 .../util/http/client/FriendlyServersTest.java |  2 +-
 .../util/http/client/JankyServersTest.java    |  2 +-
 .../java/util/metrics/cgroups/TestUtils.java  |  6 +-
 .../wikipedia/WikipediaIrcDecoder.java        | 32 +++----
 .../storage/azure/AzureDataSegmentPusher.java |  2 +-
 .../azure/AzureDataSegmentPusherTest.java     |  3 +-
 .../storage/cloudfiles/CloudFilesUtils.java   |  2 +-
 .../google/GoogleDataSegmentKiller.java       |  2 +-
 .../druid/storage/google/GoogleTaskLogs.java  |  4 +-
 .../druid/storage/google/GoogleUtils.java     |  6 +-
 .../google/GoogleDataSegmentKillerTest.java   |  2 +-
 .../emitter/graphite/GraphiteEmitter.java     |  2 +-
 .../druid/data/input/influx/InfluxParser.java |  9 +-
 .../MaterializedViewQuery.java                |  4 +-
 .../emitter/opentsdb/EventConverter.java      | 10 +-
 .../input/orc/OrcHadoopInputRowParser.java    | 12 ++-
 .../druid/emitter/statsd/StatsDEmitter.java   | 17 ++--
 .../input/AvroStreamInputRowParserTest.java   | 19 ++--
 .../hll/HllSketchAggregatorFactory.java       | 16 ++--
 .../theta/SketchEstimateWithErrorBounds.java  | 10 +-
 .../druid/query/filter/BloomKFilter.java      |  2 +-
 .../storage/hdfs/HdfsDataSegmentFinder.java   |  2 +-
 .../storage/hdfs/HdfsDataSegmentPusher.java   |  2 +-
 .../storage/hdfs/tasklog/HdfsTaskLogs.java    |  4 +-
 .../loading/HdfsDataSegmentFinderTest.java    |  4 +-
 .../hdfs/HdfsDataSegmentPullerTest.java       |  6 +-
 .../hdfs/HdfsDataSegmentPusherTest.java       |  6 +-
 .../lookup/KafkaLookupExtractorFactory.java   |  2 +-
 .../namespace/UriCacheGeneratorTest.java      |  3 +-
 .../cache/loading/OffHeapLoadingCache.java    |  2 +-
 .../storage/mysql/MySQLConnector.java         |  2 +-
 .../protobuf/ProtobufInputRowParser.java      |  2 +-
 .../firehose/s3/StaticS3FirehoseFactory.java  |  4 +-
 .../org/apache/druid/storage/s3/S3Utils.java  |  6 +-
 .../storage/s3/S3DataSegmentPusherTest.java   |  3 +-
 .../indexer/HadoopDruidIndexerConfig.java     |  7 +-
 .../org/apache/druid/indexer/JobHelper.java   |  6 +-
 .../java/org/apache/druid/indexer/Utils.java  |  6 +-
 .../indexer/updater/HadoopConverterJob.java   |  2 +-
 .../org/apache/druid/indexer/UtilsTest.java   |  2 +-
 .../autoscaling/ec2/StringEC2UserData.java    | 24 ++---
 .../overlord/http/OverlordResource.java       |  2 +-
 .../common/task/MergeTaskBaseTest.java        |  2 +-
 .../OverlordSecurityResourceFilterTest.java   |  4 +-
 .../CoordinatorResourceTestClient.java        |  3 +-
 .../druid/tests/hadoop/ITHadoopIndexTest.java |  3 +-
 .../AbstractITRealtimeIndexTaskTest.java      | 24 ++---
 ...penderatorDriverRealtimeIndexTaskTest.java |  3 +-
 .../tests/indexer/ITCompactionTaskTest.java   |  4 +-
 .../indexer/ITKafkaIndexingServiceTest.java   | 28 +++---
 .../druid/tests/indexer/ITKafkaTest.java      | 36 ++++----
 .../indexer/ITRealtimeIndexTaskTest.java      |  3 +-
 .../druid/tests/indexer/ITUnionQueryTest.java |  6 +-
 pom.xml                                       |  2 +-
 .../bitmap/WrappedConciseBitmap.java          |  2 +-
 .../bitmap/WrappedImmutableConciseBitmap.java |  2 +-
 .../bitmap/WrappedImmutableRoaringBitmap.java |  2 +-
 .../bitmap/WrappedRoaringBitmap.java          |  2 +-
 .../query/extraction/CascadeExtractionFn.java |  3 +-
 .../StringRuntimeShape.java                   |  2 +-
 .../search/BySegmentSearchResultValue.java    |  2 +-
 .../query/topn/BySegmentTopNResultValue.java  |  2 +-
 .../collections/bitmap/BitmapBenchmark.java   |  4 +-
 .../druid/segment/filter/BaseFilterTest.java  |  8 +-
 .../client/coordinator/CoordinatorClient.java |  2 +-
 .../discovery/CuratorServiceUtils.java        |  2 +-
 .../loading/LocalDataSegmentPusher.java       |  2 +-
 .../EventReceiverFirehoseFactory.java         |  5 +-
 .../realtime/plumber/RealtimePlumber.java     | 11 ++-
 .../druid/server/coordination/ServerType.java |  4 +-
 .../server/http/DatasourcesResource.java      |  6 +-
 .../druid/server/http/IntervalsResource.java  |  2 +-
 .../druid/server/metrics/MonitorsConfig.java  |  9 +-
 .../apache/druid/curator/CuratorTestBase.java |  2 +-
 .../discovery/ServiceAnnouncerTest.java       |  2 +-
 .../druid/metadata/TestDerbyConnector.java    |  2 +-
 .../loading/LocalDataSegmentPusherTest.java   |  7 +-
 .../AsyncQueryForwardingServletTest.java      |  7 +-
 .../server/http/DatasourcesResourceTest.java  |  2 +-
 .../security/SecurityResourceFilterTest.java  |  5 +-
 .../server/log/FileRequestLoggerTest.java     |  2 +-
 .../druid/cli/convert/PrefixRename.java       | 69 --------------
 .../druid/sql/avatica/AvaticaMonitor.java     |  3 +-
 .../druid/sql/calcite/planner/Calcites.java   | 15 ++-
 .../sql/calcite/schema/SystemSchema.java      |  2 +-
 .../calcite/expression/ExpressionsTest.java   |  4 +-
 101 files changed, 400 insertions(+), 338 deletions(-)
 delete mode 100644 services/src/main/java/org/apache/druid/cli/convert/PrefixRename.java

diff --git a/.idea/inspectionProfiles/Druid.xml b/.idea/inspectionProfiles/Druid.xml
index 4ada21411dc..97f079fc0fa 100644
--- a/.idea/inspectionProfiles/Druid.xml
+++ b/.idea/inspectionProfiles/Druid.xml
@@ -62,6 +62,7 @@
     <inspection_tool class="ForLoopThatDoesntUseLoopVariable" enabled="true" level="ERROR" enabled_by_default="true" />
     <inspection_tool class="HashCodeUsesNonFinalVariable" enabled="true" level="WARNING" enabled_by_default="true" />
     <inspection_tool class="ImplicitArrayToString" enabled="true" level="ERROR" enabled_by_default="true" />
+    <inspection_tool class="IndexOfReplaceableByContains" enabled="true" level="ERROR" enabled_by_default="true" />
     <inspection_tool class="InfiniteRecursion" enabled="true" level="ERROR" enabled_by_default="true" />
     <inspection_tool class="InjectedReferences" enabled="true" level="WARNING" enabled_by_default="true" />
     <inspection_tool class="InnerClassReferencedViaSubclass" enabled="true" level="ERROR" enabled_by_default="true" />
@@ -71,6 +72,8 @@
     <inspection_tool class="IteratorHasNextCallsIteratorNext" enabled="true" level="ERROR" enabled_by_default="true" />
     <inspection_tool class="IteratorNextDoesNotThrowNoSuchElementException" enabled="true" level="WARNING" enabled_by_default="true" />
     <inspection_tool class="JsonStandardCompliance" enabled="true" level="WARNING" enabled_by_default="true" />
+    <inspection_tool class="LengthOneStringInIndexOf" enabled="true" level="ERROR" enabled_by_default="true" />
+    <inspection_tool class="ListIndexOfReplaceableByContains" enabled="true" level="ERROR" enabled_by_default="true" />
     <inspection_tool class="MalformedFormatString" enabled="true" level="ERROR" enabled_by_default="true">
       <option name="additionalClasses" value="org.apache.druid.java.util.common.StringUtils,org.apache.druid.java.util.common.logger.Logger" />
       <option name="additionalMethods" value="trace,debug,info,warn,error,wtf,format,nonStrictFormat" />
@@ -112,10 +115,13 @@
     <inspection_tool class="ObjectEqualsNull" enabled="true" level="ERROR" enabled_by_default="true" />
     <inspection_tool class="ObjectToString" enabled="true" level="ERROR" enabled_by_default="true" />
     <inspection_tool class="OverwrittenKey" enabled="true" level="ERROR" enabled_by_default="true" />
+    <inspection_tool class="PointlessIndexOfComparison" enabled="true" level="ERROR" enabled_by_default="true" />
     <inspection_tool class="PrimitiveArrayArgumentToVariableArgMethod" enabled="true" level="ERROR" enabled_by_default="true" />
+    <inspection_tool class="RedundantStringOperation" enabled="true" level="ERROR" enabled_by_default="true" />
     <inspection_tool class="RedundantThrows" enabled="true" level="ERROR" enabled_by_default="true" />
     <inspection_tool class="RedundantTypeArguments" enabled="true" level="ERROR" enabled_by_default="true" />
     <inspection_tool class="ReflectionForUnavailableAnnotation" enabled="true" level="ERROR" enabled_by_default="true" />
+    <inspection_tool class="RemoveToStringInStringTemplate" enabled="true" level="WARNING" enabled_by_default="true" />
     <inspection_tool class="ReplaceAllDot" enabled="true" level="ERROR" enabled_by_default="true" />
     <inspection_tool class="ResultOfObjectAllocationIgnored" enabled="true" level="WARNING" enabled_by_default="true">
       <scope name="Production" level="ERROR" enabled="true" />
@@ -251,6 +257,7 @@
     <inspection_tool class="ToArrayCallWithZeroLengthArrayArgument" enabled="true" level="WARNING" enabled_by_default="true">
       <option name="myMode" value="BY_LEVEL" />
     </inspection_tool>
+    <inspection_tool class="UnnecessaryCallToStringValueOf" enabled="true" level="ERROR" enabled_by_default="true" />
     <inspection_tool class="UnnecessaryEnumModifier" enabled="true" level="ERROR" enabled_by_default="true" />
     <inspection_tool class="UnnecessaryFullyQualifiedName" enabled="true" level="WARNING" enabled_by_default="true">
       <scope name="NonGeneratedFiles" level="ERROR" enabled="true">
@@ -261,6 +268,7 @@
       <option name="ignoreInModuleStatements" value="true" />
     </inspection_tool>
     <inspection_tool class="UnnecessaryInterfaceModifier" enabled="true" level="ERROR" enabled_by_default="true" />
+    <inspection_tool class="UnnecessaryToStringCall" enabled="true" level="ERROR" enabled_by_default="true" />
     <inspection_tool class="UnusedAssignment" enabled="true" level="ERROR" enabled_by_default="true">
       <option name="REPORT_PREFIX_EXPRESSIONS" value="true" />
       <option name="REPORT_POSTFIX_EXPRESSIONS" value="true" />
diff --git a/benchmarks/src/main/java/org/apache/druid/benchmark/DimensionPredicateFilterBenchmark.java b/benchmarks/src/main/java/org/apache/druid/benchmark/DimensionPredicateFilterBenchmark.java
index fc9c969e9ea..6f7a2bb09b5 100644
--- a/benchmarks/src/main/java/org/apache/druid/benchmark/DimensionPredicateFilterBenchmark.java
+++ b/benchmarks/src/main/java/org/apache/druid/benchmark/DimensionPredicateFilterBenchmark.java
@@ -79,7 +79,7 @@ public class DimensionPredicateFilterBenchmark
               if (input == null) {
                 return false;
               }
-              return Integer.parseInt(input.toString()) % 2 == 0;
+              return Integer.parseInt(input) % 2 == 0;
             }
           };
         }
diff --git a/benchmarks/src/main/java/org/apache/druid/benchmark/FloatCompressionBenchmarkFileGenerator.java b/benchmarks/src/main/java/org/apache/druid/benchmark/FloatCompressionBenchmarkFileGenerator.java
index 68c92f95320..eacbc16b5d9 100644
--- a/benchmarks/src/main/java/org/apache/druid/benchmark/FloatCompressionBenchmarkFileGenerator.java
+++ b/benchmarks/src/main/java/org/apache/druid/benchmark/FloatCompressionBenchmarkFileGenerator.java
@@ -139,7 +139,7 @@ public class FloatCompressionBenchmarkFileGenerator
     // create compressed files using all combinations of CompressionStrategy and FloatEncoding provided
     for (Map.Entry<String, BenchmarkColumnValueGenerator> entry : generators.entrySet()) {
       for (CompressionStrategy compression : compressions) {
-        String name = entry.getKey() + "-" + compression.toString();
+        String name = entry.getKey() + "-" + compression;
         log.info("%s: ", name);
         File compFile = new File(dir, name);
         compFile.delete();
diff --git a/benchmarks/src/main/java/org/apache/druid/benchmark/LongCompressionBenchmarkFileGenerator.java b/benchmarks/src/main/java/org/apache/druid/benchmark/LongCompressionBenchmarkFileGenerator.java
index 6a71ddca289..68e3ae7623a 100644
--- a/benchmarks/src/main/java/org/apache/druid/benchmark/LongCompressionBenchmarkFileGenerator.java
+++ b/benchmarks/src/main/java/org/apache/druid/benchmark/LongCompressionBenchmarkFileGenerator.java
@@ -132,7 +132,7 @@ public class LongCompressionBenchmarkFileGenerator
     for (Map.Entry<String, BenchmarkColumnValueGenerator> entry : generators.entrySet()) {
       for (CompressionStrategy compression : compressions) {
         for (CompressionFactory.LongEncodingStrategy encoding : encodings) {
-          String name = entry.getKey() + "-" + compression.toString() + "-" + encoding.toString();
+          String name = entry.getKey() + "-" + compression + "-" + encoding;
           log.info("%s: ", name);
           File compFile = new File(dir, name);
           compFile.delete();
diff --git a/benchmarks/src/test/java/org/apache/druid/benchmark/BenchmarkDataGeneratorTest.java b/benchmarks/src/test/java/org/apache/druid/benchmark/BenchmarkDataGeneratorTest.java
index a1ed3949919..035e33079ce 100644
--- a/benchmarks/src/test/java/org/apache/druid/benchmark/BenchmarkDataGeneratorTest.java
+++ b/benchmarks/src/test/java/org/apache/druid/benchmark/BenchmarkDataGeneratorTest.java
@@ -443,7 +443,7 @@ public class BenchmarkDataGeneratorTest
         Collections.sort(valList);
 
         for (Comparable val : valList) {
-          System.out.println(" VAL: " + val.toString() + " CNT: " + valueMap.get(val));
+          System.out.println(" VAL: " + val + " CNT: " + valueMap.get(val));
         }
         System.out.println();
       }
diff --git a/codestyle/druid-forbidden-apis.txt b/codestyle/druid-forbidden-apis.txt
index eaa0673ba53..be5c40ffe7a 100644
--- a/codestyle/druid-forbidden-apis.txt
+++ b/codestyle/druid-forbidden-apis.txt
@@ -22,6 +22,11 @@ com.google.common.collect.Sets#newTreeSet() @ Create java.util.TreeSet directly
 com.google.common.collect.Sets#newTreeSet(java.util.Comparator) @ Create java.util.TreeSet directly
 com.google.common.util.concurrent.Futures#transform(com.google.common.util.concurrent.ListenableFuture, com.google.common.util.concurrent.AsyncFunction) @ Use org.apache.druid.java.util.common.concurrent.ListenableFutures#transformAsync
 java.io.File#toURL() @ Use java.io.File#toURI() and java.net.URI#toURL() instead
+java.lang.String#matches(java.lang.String) @ Use startsWith(), endsWith(), contains(), or compile and cache a Pattern explicitly
+java.lang.String#replace(java.lang.CharSequence,java.lang.CharSequence) @ Use one of the appropriate methods in StringUtils instead
+java.lang.String#replaceAll(java.lang.String,java.lang.String) @ Use one of the appropriate methods in StringUtils instead, or compile and cache a Pattern explicitly
+java.lang.String#replaceFirst(java.lang.String,java.lang.String) @ Use String.indexOf() and substring methods, or compile and cache a Pattern explicitly
 java.util.LinkedList @ Use ArrayList or ArrayDeque instead
 java.util.Random#<init>() @ Use ThreadLocalRandom.current() or the constructor with a seed (the latter in tests only!)
+java.util.regex.Pattern#matches(java.lang.String,java.lang.CharSequence) @ Use String.startsWith(), endsWith(), contains(), or compile and cache a Pattern explicitly
 org.apache.commons.io.FileUtils#getTempDirectory() @ Use org.junit.rules.TemporaryFolder for tests instead
\ No newline at end of file
diff --git a/core/src/main/java/org/apache/druid/java/util/common/StringUtils.java b/core/src/main/java/org/apache/druid/java/util/common/StringUtils.java
index e4020990a6a..85f71d8a7a7 100644
--- a/core/src/main/java/org/apache/druid/java/util/common/StringUtils.java
+++ b/core/src/main/java/org/apache/druid/java/util/common/StringUtils.java
@@ -153,16 +153,6 @@ public class StringUtils
     return s.toUpperCase(Locale.ENGLISH);
   }
 
-  public static String removeChar(String s, char c)
-  {
-    for (int i = 0; i < s.length(); i++) {
-      if (s.charAt(i) == c) {
-        return removeChar(s, c, i);
-      }
-    }
-    return s;
-  }
-
   public static String urlEncode(String s)
   {
     try {
@@ -173,16 +163,81 @@ public class StringUtils
     }
   }
 
-  private static String removeChar(String s, char c, int firstOccurranceIndex)
+  /**
+   * Removes all occurrences of the given char from the given string. This method is an optimal version of
+   * {@link String#replace(CharSequence, CharSequence) s.replace("c", "")}.
+   */
+  public static String removeChar(String s, char c)
   {
-    StringBuilder sb = new StringBuilder(s.length() - 1);
-    sb.append(s, 0, firstOccurranceIndex);
-    for (int i = firstOccurranceIndex + 1; i < s.length(); i++) {
-      char charOfString = s.charAt(i);
-      if (charOfString != c) {
-        sb.append(charOfString);
-      }
+    int pos = s.indexOf(c);
+    if (pos < 0) {
+      return s;
     }
+    StringBuilder sb = new StringBuilder(s.length() - 1);
+    int prevPos = 0;
+    do {
+      sb.append(s, prevPos, pos);
+      prevPos = pos + 1;
+      pos = s.indexOf(c, pos + 1);
+    } while (pos > 0);
+    sb.append(s, prevPos, s.length());
+    return sb.toString();
+  }
+
+  /**
+   * Replaces all occurrences of the given char in the given string with the given replacement string. This method is an
+   * optimal version of {@link String#replace(CharSequence, CharSequence) s.replace("c", replacement)}.
+   */
+  public static String replaceChar(String s, char c, String replacement)
+  {
+    int pos = s.indexOf(c);
+    if (pos < 0) {
+      return s;
+    }
+    StringBuilder sb = new StringBuilder(s.length() - 1 + replacement.length());
+    int prevPos = 0;
+    do {
+      sb.append(s, prevPos, pos);
+      sb.append(replacement);
+      prevPos = pos + 1;
+      pos = s.indexOf(c, pos + 1);
+    } while (pos > 0);
+    sb.append(s, prevPos, s.length());
+    return sb.toString();
+  }
+
+  /**
+   * Replaces all occurrences of the given target substring in the given string with the given replacement string. This
+   * method is an optimal version of {@link String#replace(CharSequence, CharSequence) s.replace(target, replacement)}.
+   */
+  public static String replace(String s, String target, String replacement)
+  {
+    // String.replace() is suboptimal in JDK8, but is fixed in JDK9+. When the minimal JDK version supported by Druid is
+    // JDK9+, the implementation of this method should be replaced with simple delegation to String.replace(). However,
+    // the method should still be prohibited to use in all other places except this method body, because it's easy to
+    // suboptimally call String.replace("a", "b"), String.replace("a", ""), String.replace("a", "abc"), which have
+    // better alternatives String.replace('a', 'b'), removeChar() and replaceChar() respectively.
+    int pos = s.indexOf(target);
+    if (pos < 0) {
+      return s;
+    }
+    int sLength = s.length();
+    int targetLength = target.length();
+    // This is needed to work correctly with empty target string and mimic String.replace() behavior
+    int searchSkip = Math.max(targetLength, 1);
+    StringBuilder sb = new StringBuilder(sLength - targetLength + replacement.length());
+    int prevPos = 0;
+    do {
+      sb.append(s, prevPos, pos);
+      sb.append(replacement);
+      prevPos = pos + targetLength;
+      // Break from the loop if the target is empty
+      if (pos == sLength) {
+        break;
+      }
+      pos = s.indexOf(target, pos + searchSkip);
+    } while (pos > 0);
+    sb.append(s, prevPos, sLength);
     return sb.toString();
   }
 
diff --git a/core/src/main/java/org/apache/druid/java/util/common/granularity/PeriodGranularity.java b/core/src/main/java/org/apache/druid/java/util/common/granularity/PeriodGranularity.java
index e8f88da949f..a88d53088ad 100644
--- a/core/src/main/java/org/apache/druid/java/util/common/granularity/PeriodGranularity.java
+++ b/core/src/main/java/org/apache/druid/java/util/common/granularity/PeriodGranularity.java
@@ -139,8 +139,7 @@ public class PeriodGranularity extends Granularity implements JsonSerializable
   @Override
   public byte[] getCacheKey()
   {
-    return StringUtils.toUtf8(getPeriod().toString() + ":" +
-                              getTimeZone().toString() + ":" + getOrigin());
+    return StringUtils.toUtf8(getPeriod() + ":" + getTimeZone() + ":" + getOrigin());
   }
 
   @Override
@@ -420,8 +419,7 @@ public class PeriodGranularity extends Granularity implements JsonSerializable
       return t - offset;
     } else {
       throw new UnsupportedOperationException(
-          "Period cannot be converted to milliseconds as some fields mays vary in length with chronology "
-          + chronology.toString()
+          "Period cannot be converted to milliseconds as some fields mays vary in length with chronology " + chronology
       );
     }
   }
diff --git a/core/src/main/java/org/apache/druid/java/util/emitter/core/ParametrizedUriEmitter.java b/core/src/main/java/org/apache/druid/java/util/emitter/core/ParametrizedUriEmitter.java
index bcdf887b95e..2588b32614b 100644
--- a/core/src/main/java/org/apache/druid/java/util/emitter/core/ParametrizedUriEmitter.java
+++ b/core/src/main/java/org/apache/druid/java/util/emitter/core/ParametrizedUriEmitter.java
@@ -22,6 +22,7 @@ package org.apache.druid.java.util.emitter.core;
 import com.fasterxml.jackson.databind.ObjectMapper;
 import com.google.common.base.Throwables;
 import com.google.common.collect.ImmutableSet;
+import org.apache.druid.java.util.common.StringUtils;
 import org.apache.druid.java.util.common.lifecycle.Lifecycle;
 import org.apache.druid.java.util.common.lifecycle.LifecycleStart;
 import org.apache.druid.java.util.common.lifecycle.LifecycleStop;
@@ -48,7 +49,7 @@ public class ParametrizedUriEmitter implements Flushable, Closeable, Emitter
     final ParametrizedUriExtractor parametrizedUriExtractor = new ParametrizedUriExtractor(baseUri);
     UriExtractor uriExtractor = parametrizedUriExtractor;
     if (ONLY_FEED_PARAM.equals(parametrizedUriExtractor.getParams())) {
-      uriExtractor = new FeedUriExtractor(baseUri.replace("{feed}", "%s"));
+      uriExtractor = new FeedUriExtractor(StringUtils.replace(baseUri, "{feed}", "%s"));
     }
     return uriExtractor;
   }
diff --git a/core/src/main/java/org/apache/druid/java/util/emitter/core/ParametrizedUriExtractor.java b/core/src/main/java/org/apache/druid/java/util/emitter/core/ParametrizedUriExtractor.java
index 9dcde242b87..9bd7ebbfb18 100644
--- a/core/src/main/java/org/apache/druid/java/util/emitter/core/ParametrizedUriExtractor.java
+++ b/core/src/main/java/org/apache/druid/java/util/emitter/core/ParametrizedUriExtractor.java
@@ -65,7 +65,7 @@ public class ParametrizedUriExtractor implements UriExtractor
             eventMap
         );
       }
-      processedUri = processedUri.replace(StringUtils.format("{%s}", key), paramValue.toString());
+      processedUri = StringUtils.replace(processedUri, StringUtils.format("{%s}", key), paramValue.toString());
     }
     return new URI(processedUri);
   }
diff --git a/core/src/main/java/org/apache/druid/math/expr/Expr.java b/core/src/main/java/org/apache/druid/math/expr/Expr.java
index fd45a653ac6..cce15b662c2 100644
--- a/core/src/main/java/org/apache/druid/math/expr/Expr.java
+++ b/core/src/main/java/org/apache/druid/math/expr/Expr.java
@@ -294,7 +294,7 @@ class UnaryMinusExpr extends UnaryExpr
   @Override
   public String toString()
   {
-    return "-" + expr.toString();
+    return "-" + expr;
   }
 }
 
@@ -321,7 +321,7 @@ class UnaryNotExpr extends UnaryExpr
   @Override
   public String toString()
   {
-    return "!" + expr.toString();
+    return "!" + expr;
   }
 }
 
diff --git a/core/src/main/java/org/apache/druid/math/expr/Function.java b/core/src/main/java/org/apache/druid/math/expr/Function.java
index 35217085f93..24247558c13 100644
--- a/core/src/main/java/org/apache/druid/math/expr/Function.java
+++ b/core/src/main/java/org/apache/druid/math/expr/Function.java
@@ -1033,14 +1033,12 @@ interface Function
       }
 
       final String arg = args.get(0).eval(bindings).asString();
-      final String pattern = args.get(1).eval(bindings).asString();
-      final String replacement = args.get(2).eval(bindings).asString();
+      final String pattern = NullHandling.nullToEmptyIfNeeded(args.get(1).eval(bindings).asString());
+      final String replacement = NullHandling.nullToEmptyIfNeeded(args.get(2).eval(bindings).asString());
       if (arg == null) {
         return ExprEval.of(NullHandling.defaultStringValue());
       }
-      return ExprEval.of(
-          arg.replace(NullHandling.nullToEmptyIfNeeded(pattern), NullHandling.nullToEmptyIfNeeded(replacement))
-      );
+      return ExprEval.of(StringUtils.replace(arg, pattern, replacement));
     }
   }
 
diff --git a/core/src/test/java/org/apache/druid/common/utils/UUIDUtilsTest.java b/core/src/test/java/org/apache/druid/common/utils/UUIDUtilsTest.java
index 2a6c366c5ed..d822d228066 100644
--- a/core/src/test/java/org/apache/druid/common/utils/UUIDUtilsTest.java
+++ b/core/src/test/java/org/apache/druid/common/utils/UUIDUtilsTest.java
@@ -24,6 +24,7 @@ import com.google.common.base.Joiner;
 import com.google.common.base.Strings;
 import com.google.common.collect.Collections2;
 import com.google.common.collect.Lists;
+import org.apache.druid.java.util.common.StringUtils;
 import org.junit.Assert;
 import org.junit.Test;
 import org.junit.runner.RunWith;
@@ -102,7 +103,7 @@ public class UUIDUtilsTest
     strings.add(uuidString.substring(16, 20));
     strings.add(uuidString.substring(20, 32));
     UUID uuid = UUID.fromString(Joiner.on('-').join(strings));
-    Assert.assertEquals(uuid.toString().replace("-", ""), uuidString);
+    Assert.assertEquals(StringUtils.removeChar(uuid.toString(), '-'), uuidString);
   }
 
   @Test
diff --git a/core/src/test/java/org/apache/druid/java/util/common/StringUtilsTest.java b/core/src/test/java/org/apache/druid/java/util/common/StringUtilsTest.java
index 87f7afad3f6..53f4942cf24 100644
--- a/core/src/test/java/org/apache/druid/java/util/common/StringUtilsTest.java
+++ b/core/src/test/java/org/apache/druid/java/util/common/StringUtilsTest.java
@@ -118,11 +118,34 @@ public class StringUtilsTest
   }
 
   @Test
-  public void testRemoveCharacter()
+  public void testRemoveChar()
   {
     Assert.assertEquals("123", StringUtils.removeChar("123", ','));
     Assert.assertEquals("123", StringUtils.removeChar("123,", ','));
     Assert.assertEquals("123", StringUtils.removeChar(",1,,2,3,", ','));
     Assert.assertEquals("", StringUtils.removeChar(",,", ','));
   }
+
+  @Test
+  public void testReplaceChar()
+  {
+    Assert.assertEquals("123", StringUtils.replaceChar("123", ',', "x"));
+    Assert.assertEquals("12345", StringUtils.replaceChar("123,", ',', "45"));
+    Assert.assertEquals("", StringUtils.replaceChar("", 'a', "bb"));
+    Assert.assertEquals("bb", StringUtils.replaceChar("a", 'a', "bb"));
+    Assert.assertEquals("bbbb", StringUtils.replaceChar("aa", 'a', "bb"));
+  }
+
+  @Test
+  public void testReplace()
+  {
+    Assert.assertEquals("x1x2x3x", StringUtils.replace("123", "", "x"));
+    Assert.assertEquals("12345", StringUtils.replace("123,", ",", "45"));
+    Assert.assertEquals("", StringUtils.replace("", "a", "bb"));
+    Assert.assertEquals("bb", StringUtils.replace("a", "a", "bb"));
+    Assert.assertEquals("bba", StringUtils.replace("aaa", "aa", "bb"));
+    Assert.assertEquals("bcb", StringUtils.replace("aacaa", "aa", "b"));
+    Assert.assertEquals("bb", StringUtils.replace("aaaa", "aa", "b"));
+    Assert.assertEquals("", StringUtils.replace("aaaa", "aa", ""));
+  }
 }
diff --git a/core/src/test/java/org/apache/druid/java/util/emitter/core/ParametrizedUriEmitterTest.java b/core/src/test/java/org/apache/druid/java/util/emitter/core/ParametrizedUriEmitterTest.java
index 64d0eed1f8e..40f79dd167b 100644
--- a/core/src/test/java/org/apache/druid/java/util/emitter/core/ParametrizedUriEmitterTest.java
+++ b/core/src/test/java/org/apache/druid/java/util/emitter/core/ParametrizedUriEmitterTest.java
@@ -137,7 +137,7 @@ public class ParametrizedUriEmitterTest
           protected ListenableFuture<Response> go(Request request)
           {
             results.put(
-                request.getUrl().toString(),
+                request.getUrl(),
                 StandardCharsets.UTF_8.decode(request.getByteBufferData().slice()).toString()
             );
             return GoHandlers.immediateFuture(okResponse());
diff --git a/core/src/test/java/org/apache/druid/java/util/http/client/FriendlyServersTest.java b/core/src/test/java/org/apache/druid/java/util/http/client/FriendlyServersTest.java
index 2a47033c52c..bad035032c6 100644
--- a/core/src/test/java/org/apache/druid/java/util/http/client/FriendlyServersTest.java
+++ b/core/src/test/java/org/apache/druid/java/util/http/client/FriendlyServersTest.java
@@ -238,7 +238,7 @@ public class FriendlyServersTest
         }
 
         Assert.assertTrue("ChannelException thrown by 'get'", ea instanceof ChannelException);
-        Assert.assertTrue("Expected error message", ea.getCause().getMessage().matches(".*Failed to handshake.*"));
+        Assert.assertTrue("Expected error message", ea.getCause().getMessage().contains("Failed to handshake"));
       }
 
       {
diff --git a/core/src/test/java/org/apache/druid/java/util/http/client/JankyServersTest.java b/core/src/test/java/org/apache/druid/java/util/http/client/JankyServersTest.java
index 41724548543..77ca8e34599 100644
--- a/core/src/test/java/org/apache/druid/java/util/http/client/JankyServersTest.java
+++ b/core/src/test/java/org/apache/druid/java/util/http/client/JankyServersTest.java
@@ -298,7 +298,7 @@ public class JankyServersTest
   public boolean isChannelClosedException(Throwable e)
   {
     return e instanceof ChannelException ||
-           (e instanceof IOException && e.getMessage().matches(".*Connection reset by peer.*"));
+           (e instanceof IOException && e.getMessage().contains("Connection reset by peer"));
   }
 
   @Test
diff --git a/core/src/test/java/org/apache/druid/java/util/metrics/cgroups/TestUtils.java b/core/src/test/java/org/apache/druid/java/util/metrics/cgroups/TestUtils.java
index a69d30a74e6..1ba0bb136d1 100644
--- a/core/src/test/java/org/apache/druid/java/util/metrics/cgroups/TestUtils.java
+++ b/core/src/test/java/org/apache/druid/java/util/metrics/cgroups/TestUtils.java
@@ -25,7 +25,6 @@ import org.junit.Assert;
 import java.io.File;
 import java.io.IOException;
 import java.nio.file.Files;
-import java.util.regex.Pattern;
 
 public class TestUtils
 {
@@ -41,10 +40,7 @@ public class TestUtils
     final String procMountsString = StringUtils.fromUtf8(Files.readAllBytes(procMountsTemplate.toPath()));
     Files.write(
         procMounts.toPath(),
-        StringUtils.toUtf8(procMountsString.replaceAll(
-            Pattern.quote("/sys/fs/cgroup"),
-            cgroupDir.getAbsolutePath()
-        ))
+        StringUtils.toUtf8(StringUtils.replace(procMountsString, "/sys/fs/cgroup", cgroupDir.getAbsolutePath()))
     );
 
     Assert.assertTrue(new File(
diff --git a/examples/src/main/java/org/apache/druid/examples/wikipedia/WikipediaIrcDecoder.java b/examples/src/main/java/org/apache/druid/examples/wikipedia/WikipediaIrcDecoder.java
index bb90c28d44d..edefc049383 100644
--- a/examples/src/main/java/org/apache/druid/examples/wikipedia/WikipediaIrcDecoder.java
+++ b/examples/src/main/java/org/apache/druid/examples/wikipedia/WikipediaIrcDecoder.java
@@ -46,17 +46,16 @@ import java.util.zip.GZIPInputStream;
 
 class WikipediaIrcDecoder implements IrcDecoder
 {
-  static final Logger log = new Logger(WikipediaIrcDecoder.class);
+  static final Logger LOG = new Logger(WikipediaIrcDecoder.class);
 
-  final DatabaseReader geoLookup;
-
-  static final Pattern pattern = Pattern.compile(
+  private static final Pattern PATTERN = Pattern.compile(
       ".*\\x0314\\[\\[\\x0307(.+?)\\x0314\\]\\]\\x034 (.*?)\\x0310.*\\x0302(http.+?)" +
       "\\x03.+\\x0303(.+?)\\x03.+\\x03 (\\(([+-]\\d+)\\).*|.+) \\x0310(.+)\\x03.*"
   );
 
-  static final Pattern ipPattern = Pattern.compile("\\d+.\\d+.\\d+.\\d+");
-  static final Pattern shortnamePattern = Pattern.compile("#(\\w\\w)\\..*");
+  private static final Pattern IP_PATTERN = Pattern.compile("\\d+.\\d+.\\d+.\\d+");
+  private static final Pattern SHORTNAME_PATTERN = Pattern.compile("#(\\w\\w)\\..*");
+  private static final Pattern SINGLE_SPACE_PATTERN = Pattern.compile("\\s");
 
   static final List<String> dimensionList = Lists.newArrayList(
       "page",
@@ -73,6 +72,7 @@ class WikipediaIrcDecoder implements IrcDecoder
       "city"
   );
 
+  final DatabaseReader geoLookup;
   final Map<String, Map<String, String>> namespaces;
   final String geoIpDatabase;
 
@@ -108,7 +108,7 @@ class WikipediaIrcDecoder implements IrcDecoder
       return openDefaultGeoIpDb(geoDb);
     }
     catch (RuntimeException e) {
-      log.warn(e.getMessage() + " Attempting to re-download.", e);
+      LOG.warn(e.getMessage() + " Attempting to re-download.", e);
       if (geoDb.exists() && !geoDb.delete()) {
         throw new RuntimeException("Could not delete geo db file [" + geoDb.getAbsolutePath() + "].");
       }
@@ -127,7 +127,7 @@ class WikipediaIrcDecoder implements IrcDecoder
   {
     try {
       DatabaseReader reader = new DatabaseReader(geoDb);
-      log.info("Using geo ip database at [%s].", geoDb);
+      LOG.info("Using geo ip database at [%s].", geoDb);
       return reader;
     }
     catch (IOException e) {
@@ -142,7 +142,7 @@ class WikipediaIrcDecoder implements IrcDecoder
     }
 
     try {
-      log.info("Downloading geo ip database to [%s]. This may take a few minutes.", geoDb.getAbsolutePath());
+      LOG.info("Downloading geo ip database to [%s]. This may take a few minutes.", geoDb.getAbsolutePath());
 
       File tmpFile = File.createTempFile("druid", "geo");
 
@@ -180,23 +180,23 @@ class WikipediaIrcDecoder implements IrcDecoder
     final Map<String, String> dimensions = new HashMap<>();
     final Map<String, Float> metrics = new HashMap<>();
 
-    Matcher m = pattern.matcher(msg);
+    Matcher m = PATTERN.matcher(msg);
     if (!m.matches()) {
       throw new IllegalArgumentException("Invalid input format");
     }
 
-    Matcher shortname = shortnamePattern.matcher(channel);
+    Matcher shortname = SHORTNAME_PATTERN.matcher(channel);
     if (shortname.matches()) {
       dimensions.put("language", shortname.group(1));
     }
 
     String page = m.group(1);
-    String pageUrl = page.replaceAll("\\s", "_");
+    String pageUrl = SINGLE_SPACE_PATTERN.matcher(page).replaceAll("_");
 
     dimensions.put("page", pageUrl);
 
     String user = m.group(4);
-    Matcher ipMatch = ipPattern.matcher(user);
+    Matcher ipMatch = IP_PATTERN.matcher(user);
     boolean anonymous = ipMatch.matches();
     if (anonymous) {
       try {
@@ -209,13 +209,13 @@ class WikipediaIrcDecoder implements IrcDecoder
         dimensions.put("city", lookup.getCity().getName());
       }
       catch (UnknownHostException e) {
-        log.error(e, "invalid ip [%s]", ipMatch.group());
+        LOG.error(e, "invalid ip [%s]", ipMatch.group());
       }
       catch (IOException e) {
-        log.error(e, "error looking up geo ip");
+        LOG.error(e, "error looking up geo ip");
       }
       catch (GeoIp2Exception e) {
-        log.error(e, "error looking up geo ip");
+        LOG.error(e, "error looking up geo ip");
       }
     }
     dimensions.put("user", user);
diff --git a/extensions-contrib/azure-extensions/src/main/java/org/apache/druid/storage/azure/AzureDataSegmentPusher.java b/extensions-contrib/azure-extensions/src/main/java/org/apache/druid/storage/azure/AzureDataSegmentPusher.java
index 32d749b3642..ae808125c6f 100644
--- a/extensions-contrib/azure-extensions/src/main/java/org/apache/druid/storage/azure/AzureDataSegmentPusher.java
+++ b/extensions-contrib/azure-extensions/src/main/java/org/apache/druid/storage/azure/AzureDataSegmentPusher.java
@@ -95,7 +95,7 @@ public class AzureDataSegmentPusher implements DataSegmentPusher
             dataSegment.getInterval().getStart().toString(ISODateTimeFormat.basicDateTime()),
             dataSegment.getInterval().getEnd().toString(ISODateTimeFormat.basicDateTime())
         ),
-        dataSegment.getVersion().replace(":", "_"),
+        dataSegment.getVersion().replace(':', '_'),
         dataSegment.getShardSpec().getPartitionNum(),
         useUniquePath ? DataSegmentPusher.generateUniquePath() : null
     );
diff --git a/extensions-contrib/azure-extensions/src/test/java/org/apache/druid/storage/azure/AzureDataSegmentPusherTest.java b/extensions-contrib/azure-extensions/src/test/java/org/apache/druid/storage/azure/AzureDataSegmentPusherTest.java
index 1981a78cb78..d1dfbe8b1af 100644
--- a/extensions-contrib/azure-extensions/src/test/java/org/apache/druid/storage/azure/AzureDataSegmentPusherTest.java
+++ b/extensions-contrib/azure-extensions/src/test/java/org/apache/druid/storage/azure/AzureDataSegmentPusherTest.java
@@ -42,6 +42,7 @@ import java.net.URISyntaxException;
 import java.util.ArrayList;
 import java.util.HashMap;
 import java.util.Map;
+import java.util.regex.Pattern;
 
 import static org.easymock.EasyMock.expectLastCall;
 import static org.junit.Assert.assertEquals;
@@ -119,7 +120,7 @@ public class AzureDataSegmentPusherTest extends EasyMockSupport
 
     Assert.assertTrue(
         segment.getLoadSpec().get("blobPath").toString(),
-        segment.getLoadSpec().get("blobPath").toString().matches(matcher)
+        Pattern.compile(matcher).matcher(segment.getLoadSpec().get("blobPath").toString()).matches()
     );
 
     Assert.assertEquals(segmentToPush.getSize(), segment.getSize());
diff --git a/extensions-contrib/cloudfiles-extensions/src/main/java/org/apache/druid/storage/cloudfiles/CloudFilesUtils.java b/extensions-contrib/cloudfiles-extensions/src/main/java/org/apache/druid/storage/cloudfiles/CloudFilesUtils.java
index 06722ea21b5..bc883b28fd8 100644
--- a/extensions-contrib/cloudfiles-extensions/src/main/java/org/apache/druid/storage/cloudfiles/CloudFilesUtils.java
+++ b/extensions-contrib/cloudfiles-extensions/src/main/java/org/apache/druid/storage/cloudfiles/CloudFilesUtils.java
@@ -58,7 +58,7 @@ public class CloudFilesUtils
   {
     String path = fileName;
     if (!basePath.isEmpty()) {
-      int lastSlashIndex = basePath.lastIndexOf("/");
+      int lastSlashIndex = basePath.lastIndexOf('/');
       if (lastSlashIndex != -1) {
         basePath = basePath.substring(0, lastSlashIndex);
       }
diff --git a/extensions-contrib/google-extensions/src/main/java/org/apache/druid/storage/google/GoogleDataSegmentKiller.java b/extensions-contrib/google-extensions/src/main/java/org/apache/druid/storage/google/GoogleDataSegmentKiller.java
index b3f11c481e0..4435f621c7e 100644
--- a/extensions-contrib/google-extensions/src/main/java/org/apache/druid/storage/google/GoogleDataSegmentKiller.java
+++ b/extensions-contrib/google-extensions/src/main/java/org/apache/druid/storage/google/GoogleDataSegmentKiller.java
@@ -52,7 +52,7 @@ public class GoogleDataSegmentKiller implements DataSegmentKiller
     Map<String, Object> loadSpec = segment.getLoadSpec();
     final String bucket = MapUtils.getString(loadSpec, "bucket");
     final String indexPath = MapUtils.getString(loadSpec, "path");
-    final String descriptorPath = indexPath.substring(0, indexPath.lastIndexOf("/")) + "/descriptor.json";
+    final String descriptorPath = indexPath.substring(0, indexPath.lastIndexOf('/')) + "/descriptor.json";
 
     try {
       deleteIfPresent(bucket, indexPath);
diff --git a/extensions-contrib/google-extensions/src/main/java/org/apache/druid/storage/google/GoogleTaskLogs.java b/extensions-contrib/google-extensions/src/main/java/org/apache/druid/storage/google/GoogleTaskLogs.java
index 2f747f3729c..0bb80ad9162 100644
--- a/extensions-contrib/google-extensions/src/main/java/org/apache/druid/storage/google/GoogleTaskLogs.java
+++ b/extensions-contrib/google-extensions/src/main/java/org/apache/druid/storage/google/GoogleTaskLogs.java
@@ -131,12 +131,12 @@ public class GoogleTaskLogs implements TaskLogs
 
   private String getTaskLogKey(String taskid)
   {
-    return config.getPrefix() + "/" + taskid.replaceAll(":", "_");
+    return config.getPrefix() + "/" + taskid.replace(':', '_');
   }
 
   private String getTaskReportKey(String taskid)
   {
-    return config.getPrefix() + "/" + taskid.replaceAll(":", "_") + ".report.json";
+    return config.getPrefix() + "/" + taskid.replace(':', '_') + ".report.json";
   }
 
   @Override
diff --git a/extensions-contrib/google-extensions/src/main/java/org/apache/druid/storage/google/GoogleUtils.java b/extensions-contrib/google-extensions/src/main/java/org/apache/druid/storage/google/GoogleUtils.java
index ebb47d6cf38..6f23f9ca997 100644
--- a/extensions-contrib/google-extensions/src/main/java/org/apache/druid/storage/google/GoogleUtils.java
+++ b/extensions-contrib/google-extensions/src/main/java/org/apache/druid/storage/google/GoogleUtils.java
@@ -27,14 +27,12 @@ public class GoogleUtils
 {
   public static String toFilename(String path)
   {
-    String filename = path.substring(path.lastIndexOf("/") + 1); // characters after last '/'
-    filename = filename.substring(0, filename.length());
-    return filename;
+    return path.substring(path.lastIndexOf('/') + 1); // characters after last '/'
   }
 
   public static String indexZipForSegmentPath(String path)
   {
-    return path.substring(0, path.lastIndexOf("/")) + "/index.zip";
+    return path.substring(0, path.lastIndexOf('/')) + "/index.zip";
   }
 
   public static boolean isRetryable(Throwable t)
diff --git a/extensions-contrib/google-extensions/src/test/java/org/apache/druid/storage/google/GoogleDataSegmentKillerTest.java b/extensions-contrib/google-extensions/src/test/java/org/apache/druid/storage/google/GoogleDataSegmentKillerTest.java
index 6734cb74232..6ab2a1a4bb4 100644
--- a/extensions-contrib/google-extensions/src/test/java/org/apache/druid/storage/google/GoogleDataSegmentKillerTest.java
+++ b/extensions-contrib/google-extensions/src/test/java/org/apache/druid/storage/google/GoogleDataSegmentKillerTest.java
@@ -40,7 +40,7 @@ public class GoogleDataSegmentKillerTest extends EasyMockSupport
 {
   private static final String bucket = "bucket";
   private static final String indexPath = "test/2015-04-12T00:00:00.000Z_2015-04-13T00:00:00.000Z/1/0/index.zip";
-  private static final String descriptorPath = indexPath.substring(0, indexPath.lastIndexOf("/")) + "/descriptor.json";
+  private static final String descriptorPath = indexPath.substring(0, indexPath.lastIndexOf('/')) + "/descriptor.json";
 
   private static final DataSegment dataSegment = new DataSegment(
       "test",
diff --git a/extensions-contrib/graphite-emitter/src/main/java/org/apache/druid/emitter/graphite/GraphiteEmitter.java b/extensions-contrib/graphite-emitter/src/main/java/org/apache/druid/emitter/graphite/GraphiteEmitter.java
index e80a24904c9..7fd10caec64 100644
--- a/extensions-contrib/graphite-emitter/src/main/java/org/apache/druid/emitter/graphite/GraphiteEmitter.java
+++ b/extensions-contrib/graphite-emitter/src/main/java/org/apache/druid/emitter/graphite/GraphiteEmitter.java
@@ -252,7 +252,7 @@ public class GraphiteEmitter implements Emitter
     Pattern DOT_OR_WHITESPACE = Pattern.compile("[\\s]+|[.]+");
     String sanitizedNamespace = DOT_OR_WHITESPACE.matcher(namespace).replaceAll("_");
     if (replaceSlashToDot) {
-      sanitizedNamespace = sanitizedNamespace.replace("/", ".");
+      sanitizedNamespace = sanitizedNamespace.replace('/', '.');
     }
     return sanitizedNamespace;
   }
diff --git a/extensions-contrib/influx-extensions/src/main/java/org/apache/druid/data/input/influx/InfluxParser.java b/extensions-contrib/influx-extensions/src/main/java/org/apache/druid/data/input/influx/InfluxParser.java
index db3705da65e..a090068b1fb 100644
--- a/extensions-contrib/influx-extensions/src/main/java/org/apache/druid/data/input/influx/InfluxParser.java
+++ b/extensions-contrib/influx-extensions/src/main/java/org/apache/druid/data/input/influx/InfluxParser.java
@@ -31,11 +31,16 @@ import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
+import java.util.regex.Pattern;
 
 public class InfluxParser implements Parser<String, Object>
 {
   public static final String TIMESTAMP_KEY = "__ts";
   private static final String MEASUREMENT_KEY = "measurement";
+
+  private static final Pattern BACKSLASH_PATTERN = Pattern.compile("\\\\\"");
+  private static final Pattern IDENTIFIER_PATTERN = Pattern.compile("\\\\([,= ])");
+
   private final Set<String> measurementWhitelist;
 
   public InfluxParser(Set<String> measurementWhitelist)
@@ -112,7 +117,7 @@ public class InfluxParser implements Parser<String, Object>
 
   private Object parseQuotedString(String text)
   {
-    return text.substring(1, text.length() - 1).replaceAll("\\\\\"", "\"");
+    return BACKSLASH_PATTERN.matcher(text.substring(1, text.length() - 1)).replaceAll("\"");
   }
 
   private Object parseNumber(String raw)
@@ -140,7 +145,7 @@ public class InfluxParser implements Parser<String, Object>
       return ctx.getText();
     }
 
-    return ctx.IDENTIFIER_STRING().getText().replaceAll("\\\\([,= ])", "$1");
+    return IDENTIFIER_PATTERN.matcher(ctx.IDENTIFIER_STRING().getText()).replaceAll("$1");
   }
 
   private boolean checkWhitelist(String m)
diff --git a/extensions-contrib/materialized-view-selection/src/main/java/org/apache/druid/query/materializedview/MaterializedViewQuery.java b/extensions-contrib/materialized-view-selection/src/main/java/org/apache/druid/query/materializedview/MaterializedViewQuery.java
index 26a7026027b..e0e29ee0cd0 100644
--- a/extensions-contrib/materialized-view-selection/src/main/java/org/apache/druid/query/materializedview/MaterializedViewQuery.java
+++ b/extensions-contrib/materialized-view-selection/src/main/java/org/apache/druid/query/materializedview/MaterializedViewQuery.java
@@ -208,8 +208,8 @@ public class MaterializedViewQuery<T> implements Query<T>
   public String toString()
   {
     return "MaterializedViewQuery{" +
-        "query=" + query.toString() +
-        "}";
+           "query=" + query +
+           "}";
   }
 
   @Override
diff --git a/extensions-contrib/opentsdb-emitter/src/main/java/org/apache/druid/emitter/opentsdb/EventConverter.java b/extensions-contrib/opentsdb-emitter/src/main/java/org/apache/druid/emitter/opentsdb/EventConverter.java
index dbd05684ec0..3dddd9f1616 100644
--- a/extensions-contrib/opentsdb-emitter/src/main/java/org/apache/druid/emitter/opentsdb/EventConverter.java
+++ b/extensions-contrib/opentsdb-emitter/src/main/java/org/apache/druid/emitter/opentsdb/EventConverter.java
@@ -39,8 +39,6 @@ public class EventConverter
 {
   private static final Logger log = new Logger(EventConverter.class);
   private static final Pattern WHITESPACE = Pattern.compile("[\\s]+");
-  private static final String COLON = ":";
-  private static final String DEFAULT_COLON_REPLACEMENT = "_";
 
   private final Map<String, Set<String>> metricMap;
 
@@ -51,7 +49,7 @@ public class EventConverter
 
   protected String sanitize(String metric)
   {
-    return WHITESPACE.matcher(metric.trim()).replaceAll("_").replaceAll("/", ".");
+    return WHITESPACE.matcher(metric.trim()).replaceAll("_").replace('/', '.');
   }
 
   /**
@@ -74,8 +72,8 @@ public class EventConverter
     Number value = serviceMetricEvent.getValue();
 
     Map<String, Object> tags = new HashMap<>();
-    String service = serviceMetricEvent.getService().replaceAll(COLON, DEFAULT_COLON_REPLACEMENT);
-    String host = serviceMetricEvent.getHost().replaceAll(COLON, DEFAULT_COLON_REPLACEMENT);
+    String service = serviceMetricEvent.getService().replace(':', '_');
+    String host = serviceMetricEvent.getHost().replace(':', '_');
     tags.put("service", service);
     tags.put("host", host);
 
@@ -84,7 +82,7 @@ public class EventConverter
       if (userDims.containsKey(dim)) {
         Object dimValue = userDims.get(dim);
         if (dimValue instanceof String) {
-          dimValue = ((String) dimValue).replaceAll(COLON, DEFAULT_COLON_REPLACEMENT);
+          dimValue = ((String) dimValue).replace(':', '_');
         }
         tags.put(dim, dimValue);
       }
diff --git a/extensions-contrib/orc-extensions/src/main/java/org/apache/druid/data/input/orc/OrcHadoopInputRowParser.java b/extensions-contrib/orc-extensions/src/main/java/org/apache/druid/data/input/orc/OrcHadoopInputRowParser.java
index 96a7e0bcfdc..21b249c54c3 100644
--- a/extensions-contrib/orc-extensions/src/main/java/org/apache/druid/data/input/orc/OrcHadoopInputRowParser.java
+++ b/extensions-contrib/orc-extensions/src/main/java/org/apache/druid/data/input/orc/OrcHadoopInputRowParser.java
@@ -84,9 +84,9 @@ public class OrcHadoopInputRowParser implements InputRowParser<OrcStruct>
     this.typeString = typeString == null ? typeStringFromParseSpec(parseSpec) : typeString;
     this.mapFieldNameFormat =
         mapFieldNameFormat == null ||
-        mapFieldNameFormat.indexOf(MAP_PARENT_TAG) < 0 ||
-        mapFieldNameFormat.indexOf(MAP_CHILD_TAG) < 0 ? DEFAULT_MAP_FIELD_NAME_FORMAT : mapFieldNameFormat;
-    this.mapParentFieldNameFormat = this.mapFieldNameFormat.replace(MAP_PARENT_TAG, "%s");
+        !mapFieldNameFormat.contains(MAP_PARENT_TAG) ||
+        !mapFieldNameFormat.contains(MAP_CHILD_TAG) ? DEFAULT_MAP_FIELD_NAME_FORMAT : mapFieldNameFormat;
+    this.mapParentFieldNameFormat = StringUtils.replace(this.mapFieldNameFormat, MAP_PARENT_TAG, "%s");
     this.dimensions = parseSpec.getDimensionsSpec().getDimensionNames();
     this.oip = makeObjectInspector(this.typeString);
   }
@@ -159,7 +159,11 @@ public class OrcHadoopInputRowParser implements InputRowParser<OrcStruct>
     if (mapObjectInspector.getMapSize(mapObject) < 0) {
       return;
     }
-    String mapChildFieldNameFormat = StringUtils.format(mapParentFieldNameFormat, parentName).replace(MAP_CHILD_TAG, "%s");
+    String mapChildFieldNameFormat = StringUtils.replace(
+        StringUtils.format(mapParentFieldNameFormat, parentName),
+        MAP_CHILD_TAG,
+        "%s"
+    );
 
     Map objectMap = mapObjectInspector.getMap(mapObject);
     PrimitiveObjectInspector key = (PrimitiveObjectInspector) mapObjectInspector.getMapKeyObjectInspector();
diff --git a/extensions-contrib/statsd-emitter/src/main/java/org/apache/druid/emitter/statsd/StatsDEmitter.java b/extensions-contrib/statsd-emitter/src/main/java/org/apache/druid/emitter/statsd/StatsDEmitter.java
index 5fb576ba81f..d2f40b60b47 100644
--- a/extensions-contrib/statsd-emitter/src/main/java/org/apache/druid/emitter/statsd/StatsDEmitter.java
+++ b/extensions-contrib/statsd-emitter/src/main/java/org/apache/druid/emitter/statsd/StatsDEmitter.java
@@ -25,12 +25,14 @@ import com.google.common.collect.ImmutableList;
 import com.timgroup.statsd.NonBlockingStatsDClient;
 import com.timgroup.statsd.StatsDClient;
 import com.timgroup.statsd.StatsDClientErrorHandler;
+import org.apache.druid.java.util.common.StringUtils;
 import org.apache.druid.java.util.common.logger.Logger;
 import org.apache.druid.java.util.emitter.core.Emitter;
 import org.apache.druid.java.util.emitter.core.Event;
 import org.apache.druid.java.util.emitter.service.ServiceMetricEvent;
 
 import java.util.Map;
+import java.util.regex.Pattern;
 
 /**
  */
@@ -38,9 +40,9 @@ public class StatsDEmitter implements Emitter
 {
 
   private static final Logger log = new Logger(StatsDEmitter.class);
-  private static final String DRUID_METRIC_SEPARATOR = "\\/";
-  private static final String STATSD_SEPARATOR = ":|\\|";
-  private static final String BLANK = "\\s+";
+  private static final char DRUID_METRIC_SEPARATOR = '/';
+  private static final Pattern STATSD_SEPARATOR = Pattern.compile("[:|]");
+  private static final Pattern BLANK = Pattern.compile("\\s+");
 
   static final StatsDEmitter of(StatsDEmitterConfig config, ObjectMapper mapper)
   {
@@ -101,11 +103,10 @@ public class StatsDEmitter implements Emitter
 
       if (statsDMetric != null) {
 
-        String fullName = Joiner.on(config.getSeparator())
-                                .join(nameBuilder.build())
-                                .replaceAll(DRUID_METRIC_SEPARATOR, config.getSeparator())
-                                .replaceAll(STATSD_SEPARATOR, config.getSeparator())
-                                .replaceAll(BLANK, config.getBlankHolder());
+        String fullName = Joiner.on(config.getSeparator()).join(nameBuilder.build());
+        fullName = StringUtils.replaceChar(fullName, DRUID_METRIC_SEPARATOR, config.getSeparator());
+        fullName = STATSD_SEPARATOR.matcher(fullName).replaceAll(config.getSeparator());
+        fullName = BLANK.matcher(fullName).replaceAll(config.getBlankHolder());
 
         long val = statsDMetric.convertRange ? Math.round(value.doubleValue() * 100) : value.longValue();
         switch (statsDMetric.type) {
diff --git a/extensions-core/avro-extensions/src/test/java/org/apache/druid/data/input/AvroStreamInputRowParserTest.java b/extensions-core/avro-extensions/src/test/java/org/apache/druid/data/input/AvroStreamInputRowParserTest.java
index 015ff142bf8..4da8906c9ee 100644
--- a/extensions-core/avro-extensions/src/test/java/org/apache/druid/data/input/AvroStreamInputRowParserTest.java
+++ b/extensions-core/avro-extensions/src/test/java/org/apache/druid/data/input/AvroStreamInputRowParserTest.java
@@ -64,6 +64,7 @@ import java.util.HashMap;
 import java.util.HashSet;
 import java.util.List;
 import java.util.Map;
+import java.util.regex.Pattern;
 
 import static org.junit.Assert.assertEquals;
 
@@ -150,6 +151,8 @@ public class AvroStreamInputRowParserTest
   public static final String SOME_UNION_VALUE = "string as union";
   public static final ByteBuffer SOME_BYTES_VALUE = ByteBuffer.allocate(8);
 
+  private static final Pattern BRACES_AND_SPACE = Pattern.compile("[{} ]");
+
   private final ObjectMapper jsonMapper = new ObjectMapper();
 
 
@@ -267,7 +270,7 @@ public class AvroStreamInputRowParserTest
     assertEquals(1543698L, inputRow.getTimestampFromEpoch());
 
     // test dimensions
-    assertEquals(Collections.singletonList(String.valueOf(EVENT_TYPE_VALUE)), inputRow.getDimension(EVENT_TYPE));
+    assertEquals(Collections.singletonList(EVENT_TYPE_VALUE), inputRow.getDimension(EVENT_TYPE));
     assertEquals(Collections.singletonList(String.valueOf(ID_VALUE)), inputRow.getDimension(ID));
     assertEquals(Collections.singletonList(String.valueOf(SOME_OTHER_ID_VALUE)), inputRow.getDimension(SOME_OTHER_ID));
     assertEquals(Collections.singletonList(String.valueOf(true)), inputRow.getDimension(IS_VALID));
@@ -285,9 +288,10 @@ public class AvroStreamInputRowParserTest
         SOME_INT_VALUE_MAP_VALUE,
         new HashMap<CharSequence, Integer>(
             Maps.transformValues(
-                Splitter.on(",")
-                        .withKeyValueSeparator("=")
-                        .split(inputRow.getDimension("someIntValueMap").get(0).replaceAll("[\\{\\} ]", "")),
+                Splitter
+                    .on(",")
+                    .withKeyValueSeparator("=")
+                    .split(BRACES_AND_SPACE.matcher(inputRow.getDimension("someIntValueMap").get(0)).replaceAll("")),
                 new Function<String, Integer>()
                 {
                   @Nullable
@@ -303,9 +307,10 @@ public class AvroStreamInputRowParserTest
     assertEquals(
         SOME_STRING_VALUE_MAP_VALUE,
         new HashMap<CharSequence, CharSequence>(
-            Splitter.on(",")
-                    .withKeyValueSeparator("=")
-                    .split(inputRow.getDimension("someIntValueMap").get(0).replaceAll("[\\{\\} ]", ""))
+            Splitter
+                .on(",")
+                .withKeyValueSeparator("=")
+                .split(BRACES_AND_SPACE.matcher(inputRow.getDimension("someIntValueMap").get(0)).replaceAll(""))
         )
     );
     assertEquals(Collections.singletonList(SOME_UNION_VALUE), inputRow.getDimension("someUnion"));
diff --git a/extensions-core/datasketches/src/main/java/org/apache/druid/query/aggregation/datasketches/hll/HllSketchAggregatorFactory.java b/extensions-core/datasketches/src/main/java/org/apache/druid/query/aggregation/datasketches/hll/HllSketchAggregatorFactory.java
index bb6fa9e9a8b..71a20decf69 100644
--- a/extensions-core/datasketches/src/main/java/org/apache/druid/query/aggregation/datasketches/hll/HllSketchAggregatorFactory.java
+++ b/extensions-core/datasketches/src/main/java/org/apache/druid/query/aggregation/datasketches/hll/HllSketchAggregatorFactory.java
@@ -19,24 +19,22 @@
 
 package org.apache.druid.query.aggregation.datasketches.hll;
 
-import java.util.Collections;
-import java.util.Comparator;
-import java.util.List;
-import java.util.Objects;
-
-import javax.annotation.Nullable;
-
 import com.fasterxml.jackson.annotation.JsonProperty;
 import com.yahoo.sketches.hll.HllSketch;
 import com.yahoo.sketches.hll.TgtHllType;
 import com.yahoo.sketches.hll.Union;
-
 import org.apache.druid.query.aggregation.AggregateCombiner;
 import org.apache.druid.query.aggregation.AggregatorFactory;
 import org.apache.druid.query.aggregation.ObjectAggregateCombiner;
 import org.apache.druid.query.cache.CacheKeyBuilder;
 import org.apache.druid.segment.ColumnValueSelector;
 
+import javax.annotation.Nullable;
+import java.util.Collections;
+import java.util.Comparator;
+import java.util.List;
+import java.util.Objects;
+
 /**
  * Base class for both build and merge factories
  * @author Alexander Saydakov
@@ -176,7 +174,7 @@ abstract class HllSketchAggregatorFactory extends AggregatorFactory
   @Override
   public AggregatorFactory getCombiningFactory()
   {
-    return new HllSketchMergeAggregatorFactory(getName(), getName(), getLgK(), getTgtHllType().toString());
+    return new HllSketchMergeAggregatorFactory(getName(), getName(), getLgK(), getTgtHllType());
   }
 
   @Override
diff --git a/extensions-core/datasketches/src/main/java/org/apache/druid/query/aggregation/datasketches/theta/SketchEstimateWithErrorBounds.java b/extensions-core/datasketches/src/main/java/org/apache/druid/query/aggregation/datasketches/theta/SketchEstimateWithErrorBounds.java
index 41cd7c1aa49..67f8302ec50 100644
--- a/extensions-core/datasketches/src/main/java/org/apache/druid/query/aggregation/datasketches/theta/SketchEstimateWithErrorBounds.java
+++ b/extensions-core/datasketches/src/main/java/org/apache/druid/query/aggregation/datasketches/theta/SketchEstimateWithErrorBounds.java
@@ -74,11 +74,11 @@ public class SketchEstimateWithErrorBounds
   public String toString()
   {
     return "SketchEstimateWithErrorBounds{" +
-        "estimate=" + Double.toString(estimate) +
-        ", highBound=" + Double.toString(highBound) +
-        ", lowBound=" + Double.toString(lowBound) +
-        ", numStdDev=" + Integer.toString(numStdDev) +
-        "}";
+           "estimate=" + estimate +
+           ", highBound=" + highBound +
+           ", lowBound=" + lowBound +
+           ", numStdDev=" + numStdDev +
+           "}";
   }
 
   @Override
diff --git a/extensions-core/druid-bloom-filter/src/main/java/org/apache/druid/query/filter/BloomKFilter.java b/extensions-core/druid-bloom-filter/src/main/java/org/apache/druid/query/filter/BloomKFilter.java
index 37331450692..29492872966 100644
--- a/extensions-core/druid-bloom-filter/src/main/java/org/apache/druid/query/filter/BloomKFilter.java
+++ b/extensions-core/druid-bloom-filter/src/main/java/org/apache/druid/query/filter/BloomKFilter.java
@@ -433,7 +433,7 @@ public class BloomKFilter
       this.bitSet.putAll(that.bitSet);
     } else {
       throw new IllegalArgumentException("BloomKFilters are not compatible for merging." +
-                                         " this - " + this.toString() + " that - " + that.toString());
+                                         " this - " + this + " that - " + that);
     }
   }
 
diff --git a/extensions-core/hdfs-storage/src/main/java/org/apache/druid/storage/hdfs/HdfsDataSegmentFinder.java b/extensions-core/hdfs-storage/src/main/java/org/apache/druid/storage/hdfs/HdfsDataSegmentFinder.java
index aaab1b5148a..45904d7f3bf 100644
--- a/extensions-core/hdfs-storage/src/main/java/org/apache/druid/storage/hdfs/HdfsDataSegmentFinder.java
+++ b/extensions-core/hdfs-storage/src/main/java/org/apache/druid/storage/hdfs/HdfsDataSegmentFinder.java
@@ -67,7 +67,7 @@ public class HdfsDataSegmentFinder implements DataSegmentFinder
       fs = workingDirPath.getFileSystem(config);
 
       log.info(fs.getScheme());
-      log.info("FileSystem URI:" + fs.getUri().toString());
+      log.info("FileSystem URI:" + fs.getUri());
 
       if (!fs.exists(workingDirPath)) {
         throw new SegmentLoadingException("Working directory [%s] doesn't exist.", workingDirPath);
diff --git a/extensions-core/hdfs-storage/src/main/java/org/apache/druid/storage/hdfs/HdfsDataSegmentPusher.java b/extensions-core/hdfs-storage/src/main/java/org/apache/druid/storage/hdfs/HdfsDataSegmentPusher.java
index cf6ceab4dcb..1c3f50d96a4 100644
--- a/extensions-core/hdfs-storage/src/main/java/org/apache/druid/storage/hdfs/HdfsDataSegmentPusher.java
+++ b/extensions-core/hdfs-storage/src/main/java/org/apache/druid/storage/hdfs/HdfsDataSegmentPusher.java
@@ -242,7 +242,7 @@ public class HdfsDataSegmentPusher implements DataSegmentPusher
             segment.getInterval().getStart().toString(ISODateTimeFormat.basicDateTime()),
             segment.getInterval().getEnd().toString(ISODateTimeFormat.basicDateTime())
         ),
-        segment.getVersion().replaceAll(":", "_")
+        segment.getVersion().replace(':', '_')
     );
   }
 
diff --git a/extensions-core/hdfs-storage/src/main/java/org/apache/druid/storage/hdfs/tasklog/HdfsTaskLogs.java b/extensions-core/hdfs-storage/src/main/java/org/apache/druid/storage/hdfs/tasklog/HdfsTaskLogs.java
index 94cd82856ac..2f1df6d1fab 100644
--- a/extensions-core/hdfs-storage/src/main/java/org/apache/druid/storage/hdfs/tasklog/HdfsTaskLogs.java
+++ b/extensions-core/hdfs-storage/src/main/java/org/apache/druid/storage/hdfs/tasklog/HdfsTaskLogs.java
@@ -135,7 +135,7 @@ public class HdfsTaskLogs implements TaskLogs
    */
   private Path getTaskLogFileFromId(String taskId)
   {
-    return new Path(mergePaths(config.getDirectory(), taskId.replaceAll(":", "_")));
+    return new Path(mergePaths(config.getDirectory(), taskId.replace(':', '_')));
   }
 
   /**
@@ -144,7 +144,7 @@ public class HdfsTaskLogs implements TaskLogs
    */
   private Path getTaskReportsFileFromId(String taskId)
   {
-    return new Path(mergePaths(config.getDirectory(), taskId.replaceAll(":", "_") + ".reports.json"));
+    return new Path(mergePaths(config.getDirectory(), taskId.replace(':', '_') + ".reports.json"));
   }
 
   // some hadoop version Path.mergePaths does not exist
diff --git a/extensions-core/hdfs-storage/src/test/java/org/apache/druid/segment/loading/HdfsDataSegmentFinderTest.java b/extensions-core/hdfs-storage/src/test/java/org/apache/druid/segment/loading/HdfsDataSegmentFinderTest.java
index ec8b0ea5c5b..0c5c52083e4 100644
--- a/extensions-core/hdfs-storage/src/test/java/org/apache/druid/segment/loading/HdfsDataSegmentFinderTest.java
+++ b/extensions-core/hdfs-storage/src/test/java/org/apache/druid/segment/loading/HdfsDataSegmentFinderTest.java
@@ -306,13 +306,13 @@ public class HdfsDataSegmentFinderTest
   private String getDescriptorPath(DataSegment segment)
   {
     final Path indexzip = new Path(String.valueOf(segment.getLoadSpec().get("path")));
-    return indexzip.getParent().toString() + "/" + DESCRIPTOR_JSON;
+    return indexzip.getParent() + "/" + DESCRIPTOR_JSON;
   }
 
   private String getDescriptorPathWithPartitionNum(DataSegment segment, int partitionNum)
   {
     final Path indexzip = new Path(String.valueOf(segment.getLoadSpec().get("path")));
-    return indexzip.getParent().toString() + "/" + partitionNum + "_" + DESCRIPTOR_JSON;
+    return indexzip.getParent() + "/" + partitionNum + "_" + DESCRIPTOR_JSON;
   }
 
   private String readContent(Path descriptor) throws IOException
diff --git a/extensions-core/hdfs-storage/src/test/java/org/apache/druid/storage/hdfs/HdfsDataSegmentPullerTest.java b/extensions-core/hdfs-storage/src/test/java/org/apache/druid/storage/hdfs/HdfsDataSegmentPullerTest.java
index 2924a6d51eb..86e8c5d4b25 100644
--- a/extensions-core/hdfs-storage/src/test/java/org/apache/druid/storage/hdfs/HdfsDataSegmentPullerTest.java
+++ b/extensions-core/hdfs-storage/src/test/java/org/apache/druid/storage/hdfs/HdfsDataSegmentPullerTest.java
@@ -118,7 +118,7 @@ public class HdfsDataSegmentPullerTest
 
     final File outTmpDir = com.google.common.io.Files.createTempDir();
 
-    final URI uri = URI.create(uriBase.toString() + zipPath.toString());
+    final URI uri = URI.create(uriBase.toString() + zipPath);
 
     try (final OutputStream stream = new FileOutputStream(tmpFile)) {
       ByteStreams.copy(new ByteArrayInputStream(pathByteContents), stream);
@@ -163,7 +163,7 @@ public class HdfsDataSegmentPullerTest
     final File outFile = new File(outTmpDir, "testZip");
     outFile.delete();
 
-    final URI uri = URI.create(uriBase.toString() + zipPath.toString());
+    final URI uri = URI.create(uriBase.toString() + zipPath);
 
     try (final OutputStream outputStream = miniCluster.getFileSystem().create(zipPath);
          final OutputStream gzStream = new GZIPOutputStream(outputStream);
@@ -197,7 +197,7 @@ public class HdfsDataSegmentPullerTest
     final File outFile = new File(outTmpDir, "test.txt");
     outFile.delete();
 
-    final URI uri = URI.create(uriBase.toString() + perTestPath.toString());
+    final URI uri = URI.create(uriBase.toString() + perTestPath);
 
     try (final OutputStream outputStream = miniCluster.getFileSystem().create(zipPath);
          final InputStream inputStream = new ByteArrayInputStream(pathByteContents)) {
diff --git a/extensions-core/hdfs-storage/src/test/java/org/apache/druid/storage/hdfs/HdfsDataSegmentPusherTest.java b/extensions-core/hdfs-storage/src/test/java/org/apache/druid/storage/hdfs/HdfsDataSegmentPusherTest.java
index 03f45080865..6333033c07a 100644
--- a/extensions-core/hdfs-storage/src/test/java/org/apache/druid/storage/hdfs/HdfsDataSegmentPusherTest.java
+++ b/extensions-core/hdfs-storage/src/test/java/org/apache/druid/storage/hdfs/HdfsDataSegmentPusherTest.java
@@ -68,6 +68,7 @@ import java.io.IOException;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.HashMap;
+import java.util.regex.Pattern;
 
 /**
  */
@@ -161,10 +162,11 @@ public class HdfsDataSegmentPusherTest
 
     DataSegment segment = pusher.push(segmentDir, segmentToPush, true);
 
-    String matcher = ".*/foo/20150101T000000\\.000Z_20160101T000000\\.000Z/0/0_[A-Za-z0-9-]{36}_index\\.zip";
+    Pattern pattern =
+        Pattern.compile(".*/foo/20150101T000000\\.000Z_20160101T000000\\.000Z/0/0_[A-Za-z0-9-]{36}_index\\.zip");
     Assert.assertTrue(
         segment.getLoadSpec().get("path").toString(),
-        segment.getLoadSpec().get("path").toString().matches(matcher)
+        pattern.matcher(segment.getLoadSpec().get("path").toString()).matches()
     );
   }
 
diff --git a/extensions-core/kafka-extraction-namespace/src/main/java/org/apache/druid/query/lookup/KafkaLookupExtractorFactory.java b/extensions-core/kafka-extraction-namespace/src/main/java/org/apache/druid/query/lookup/KafkaLookupExtractorFactory.java
index ced2d16c13f..4fb1a240111 100644
--- a/extensions-core/kafka-extraction-namespace/src/main/java/org/apache/druid/query/lookup/KafkaLookupExtractorFactory.java
+++ b/extensions-core/kafka-extraction-namespace/src/main/java/org/apache/druid/query/lookup/KafkaLookupExtractorFactory.java
@@ -117,7 +117,7 @@ public class KafkaLookupExtractorFactory implements LookupExtractorFactory
     this.cacheManager = cacheManager;
     this.connectTimeout = connectTimeout;
     this.injective = injective;
-    this.factoryId = "kafka-factory-" + kafkaTopic + UUID.randomUUID().toString();
+    this.factoryId = "kafka-factory-" + kafkaTopic + UUID.randomUUID();
   }
 
   public KafkaLookupExtractorFactory(
diff --git a/extensions-core/lookups-cached-global/src/test/java/org/apache/druid/server/lookup/namespace/UriCacheGeneratorTest.java b/extensions-core/lookups-cached-global/src/test/java/org/apache/druid/server/lookup/namespace/UriCacheGeneratorTest.java
index 2f2e23a2bed..87cae6af656 100644
--- a/extensions-core/lookups-cached-global/src/test/java/org/apache/druid/server/lookup/namespace/UriCacheGeneratorTest.java
+++ b/extensions-core/lookups-cached-global/src/test/java/org/apache/druid/server/lookup/namespace/UriCacheGeneratorTest.java
@@ -512,8 +512,7 @@ public class UriCacheGeneratorTest
   {
     Assert.assertNull(scheduler.scheduleAndWait(
         new UriExtractionNamespace(
-            new URI("file://tmp/I_DONT_REALLY_EXIST" +
-                    UUID.randomUUID().toString()),
+            new URI("file://tmp/I_DONT_REALLY_EXIST" + UUID.randomUUID()),
             null,
             null,
             new UriExtractionNamespace.JSONFlatDataParser(
diff --git a/extensions-core/lookups-cached-single/src/main/java/org/apache/druid/server/lookup/cache/loading/OffHeapLoadingCache.java b/extensions-core/lookups-cached-single/src/main/java/org/apache/druid/server/lookup/cache/loading/OffHeapLoadingCache.java
index e20cf77495b..a5f7949d1a1 100644
--- a/extensions-core/lookups-cached-single/src/main/java/org/apache/druid/server/lookup/cache/loading/OffHeapLoadingCache.java
+++ b/extensions-core/lookups-cached-single/src/main/java/org/apache/druid/server/lookup/cache/loading/OffHeapLoadingCache.java
@@ -192,7 +192,7 @@ public class OffHeapLoadingCache<K, V> implements LoadingCache<K, V>
   public void close()
   {
     if (!closed.getAndSet(true)) {
-      DB.delete(String.valueOf(name));
+      DB.delete(name);
     }
   }
 
diff --git a/extensions-core/mysql-metadata-storage/src/main/java/org/apache/druid/metadata/storage/mysql/MySQLConnector.java b/extensions-core/mysql-metadata-storage/src/main/java/org/apache/druid/metadata/storage/mysql/MySQLConnector.java
index ffb9567be54..f16dd8fad37 100644
--- a/extensions-core/mysql-metadata-storage/src/main/java/org/apache/druid/metadata/storage/mysql/MySQLConnector.java
+++ b/extensions-core/mysql-metadata-storage/src/main/java/org/apache/druid/metadata/storage/mysql/MySQLConnector.java
@@ -180,7 +180,7 @@ public class MySQLConnector extends SQLMetadataConnector
         .map(StringMapper.FIRST)
         .first();
 
-    if (!databaseCharset.matches("utf8.*")) {
+    if (!databaseCharset.startsWith("utf8")) {
       throw new ISE(
           "Druid requires its MySQL database to be created with an UTF8 charset, found `%1$s`. "
           + "The recommended charset is `utf8mb4`.",
diff --git a/extensions-core/protobuf-extensions/src/main/java/org/apache/druid/data/input/protobuf/ProtobufInputRowParser.java b/extensions-core/protobuf-extensions/src/main/java/org/apache/druid/data/input/protobuf/ProtobufInputRowParser.java
index e47adeeeaa8..b9075a116c5 100644
--- a/extensions-core/protobuf-extensions/src/main/java/org/apache/druid/data/input/protobuf/ProtobufInputRowParser.java
+++ b/extensions-core/protobuf-extensions/src/main/java/org/apache/druid/data/input/protobuf/ProtobufInputRowParser.java
@@ -122,7 +122,7 @@ public class ProtobufInputRowParser implements ByteBufferInputRowParser
         fin = url.openConnection().getInputStream();
       }
       catch (IOException e) {
-        throw new ParseException(e, "Cannot read descriptor file: " + url.toString());
+        throw new ParseException(e, "Cannot read descriptor file: " + url);
       }
     }
 
diff --git a/extensions-core/s3-extensions/src/main/java/org/apache/druid/firehose/s3/StaticS3FirehoseFactory.java b/extensions-core/s3-extensions/src/main/java/org/apache/druid/firehose/s3/StaticS3FirehoseFactory.java
index f3783b37e21..693f311aed9 100644
--- a/extensions-core/s3-extensions/src/main/java/org/apache/druid/firehose/s3/StaticS3FirehoseFactory.java
+++ b/extensions-core/s3-extensions/src/main/java/org/apache/druid/firehose/s3/StaticS3FirehoseFactory.java
@@ -288,9 +288,7 @@ public class StaticS3FirehoseFactory extends PrefetchableTextFilesFirehoseFactor
     final String authority = originalAuthority.endsWith("/") ?
                              originalAuthority.substring(0, originalAuthority.length() - 1) :
                              originalAuthority;
-    final String path = originalPath.startsWith("/") ?
-                        originalPath.substring(1, originalPath.length()) :
-                        originalPath;
+    final String path = originalPath.startsWith("/") ? originalPath.substring(1) : originalPath;
 
     return URI.create(StringUtils.format("s3://%s/%s", authority, path));
   }
diff --git a/extensions-core/s3-extensions/src/main/java/org/apache/druid/storage/s3/S3Utils.java b/extensions-core/s3-extensions/src/main/java/org/apache/druid/storage/s3/S3Utils.java
index ad13973f1b9..e0a3dac8cae 100644
--- a/extensions-core/s3-extensions/src/main/java/org/apache/druid/storage/s3/S3Utils.java
+++ b/extensions-core/s3-extensions/src/main/java/org/apache/druid/storage/s3/S3Utils.java
@@ -174,12 +174,12 @@ public class S3Utils
 
   static String descriptorPathForSegmentPath(String s3Path)
   {
-    return s3Path.substring(0, s3Path.lastIndexOf("/")) + "/descriptor.json";
+    return s3Path.substring(0, s3Path.lastIndexOf('/')) + "/descriptor.json";
   }
 
   static String indexZipForSegmentPath(String s3Path)
   {
-    return s3Path.substring(0, s3Path.lastIndexOf("/")) + "/index.zip";
+    return s3Path.substring(0, s3Path.lastIndexOf('/')) + "/index.zip";
   }
 
   static String toFilename(String key)
@@ -189,7 +189,7 @@ public class S3Utils
 
   static String toFilename(String key, final String suffix)
   {
-    String filename = key.substring(key.lastIndexOf("/") + 1); // characters after last '/'
+    String filename = key.substring(key.lastIndexOf('/') + 1); // characters after last '/'
     filename = filename.substring(0, filename.length() - suffix.length()); // remove the suffix from the end
     return filename;
   }
diff --git a/extensions-core/s3-extensions/src/test/java/org/apache/druid/storage/s3/S3DataSegmentPusherTest.java b/extensions-core/s3-extensions/src/test/java/org/apache/druid/storage/s3/S3DataSegmentPusherTest.java
index bc57e2a76cc..5cacf1f8fc4 100644
--- a/extensions-core/s3-extensions/src/test/java/org/apache/druid/storage/s3/S3DataSegmentPusherTest.java
+++ b/extensions-core/s3-extensions/src/test/java/org/apache/druid/storage/s3/S3DataSegmentPusherTest.java
@@ -45,6 +45,7 @@ import java.io.File;
 import java.io.FileInputStream;
 import java.util.ArrayList;
 import java.util.HashMap;
+import java.util.regex.Pattern;
 
 /**
  */
@@ -148,7 +149,7 @@ public class S3DataSegmentPusherTest
     Assert.assertEquals("bucket", segment.getLoadSpec().get("bucket"));
     Assert.assertTrue(
         segment.getLoadSpec().get("key").toString(),
-        segment.getLoadSpec().get("key").toString().matches(matcher)
+        Pattern.compile(matcher).matcher(segment.getLoadSpec().get("key").toString()).matches()
     );
     Assert.assertEquals("s3_zip", segment.getLoadSpec().get("type"));
 
diff --git a/indexing-hadoop/src/main/java/org/apache/druid/indexer/HadoopDruidIndexerConfig.java b/indexing-hadoop/src/main/java/org/apache/druid/indexer/HadoopDruidIndexerConfig.java
index d52db6eb7bf..4822e78e7e9 100644
--- a/indexing-hadoop/src/main/java/org/apache/druid/indexer/HadoopDruidIndexerConfig.java
+++ b/indexing-hadoop/src/main/java/org/apache/druid/indexer/HadoopDruidIndexerConfig.java
@@ -507,7 +507,7 @@ public class HadoopDruidIndexerConfig
             "%s/%s/%s_%s",
             getWorkingPath(),
             schema.getDataSchema().getDataSource(),
-            schema.getTuningConfig().getVersion().replace(":", ""),
+            StringUtils.removeChar(schema.getTuningConfig().getVersion(), ':'),
             schema.getUniqueId()
         )
     );
@@ -547,7 +547,10 @@ public class HadoopDruidIndexerConfig
 
   public Path makeDescriptorInfoPath(DataSegment segment)
   {
-    return new Path(makeDescriptorInfoDir(), StringUtils.format("%s.json", segment.getIdentifier().replace(":", "")));
+    return new Path(
+        makeDescriptorInfoDir(),
+        StringUtils.removeChar(StringUtils.format("%s.json", segment.getIdentifier()), ':')
+    );
   }
 
   public void addJobProperties(Job job)
diff --git a/indexing-hadoop/src/main/java/org/apache/druid/indexer/JobHelper.java b/indexing-hadoop/src/main/java/org/apache/druid/indexer/JobHelper.java
index 1a364595e62..59bc30d179d 100644
--- a/indexing-hadoop/src/main/java/org/apache/druid/indexer/JobHelper.java
+++ b/indexing-hadoop/src/main/java/org/apache/druid/indexer/JobHelper.java
@@ -766,7 +766,11 @@ public class JobHelper
       // getHdfsStorageDir. But that wouldn't fix this issue for people who already have segments with ":".
       // Because of this we just URL encode the : making everything work as it should.
       segmentLocURI = URI.create(
-          StringUtils.format("gs://%s/%s", loadSpec.get("bucket"), loadSpec.get("path").toString().replace(":", "%3A"))
+          StringUtils.format(
+              "gs://%s/%s",
+              loadSpec.get("bucket"),
+              StringUtils.replaceChar(loadSpec.get("path").toString(), ':', "%3A")
+          )
       );
     } else if ("local".equals(type)) {
       try {
diff --git a/indexing-hadoop/src/main/java/org/apache/druid/indexer/Utils.java b/indexing-hadoop/src/main/java/org/apache/druid/indexer/Utils.java
index 57883d6f66d..c45b2b6ad9f 100644
--- a/indexing-hadoop/src/main/java/org/apache/druid/indexer/Utils.java
+++ b/indexing-hadoop/src/main/java/org/apache/druid/indexer/Utils.java
@@ -58,7 +58,7 @@ public class Utils
     if (FileOutputFormat.getCompressOutput(job)) {
       codecClass = FileOutputFormat.getOutputCompressorClass(job, GzipCodec.class);
       codec = ReflectionUtils.newInstance(codecClass, job.getConfiguration());
-      outputPath = new Path(outputPath.toString() + codec.getDefaultExtension());
+      outputPath = new Path(outputPath + codec.getDefaultExtension());
     }
 
     if (fs.exists(outputPath)) {
@@ -89,7 +89,7 @@ public class Utils
     } else {
       Class<? extends CompressionCodec> codecClass = FileOutputFormat.getOutputCompressorClass(job, GzipCodec.class);
       CompressionCodec codec = ReflectionUtils.newInstance(codecClass, job.getConfiguration());
-      return fs.exists(new Path(inputPath.toString() + codec.getDefaultExtension()));
+      return fs.exists(new Path(inputPath + codec.getDefaultExtension()));
     }
   }
 
@@ -101,7 +101,7 @@ public class Utils
     } else {
       Class<? extends CompressionCodec> codecClass = FileOutputFormat.getOutputCompressorClass(job, GzipCodec.class);
       CompressionCodec codec = ReflectionUtils.newInstance(codecClass, job.getConfiguration());
-      inputPath = new Path(inputPath.toString() + codec.getDefaultExtension());
+      inputPath = new Path(inputPath + codec.getDefaultExtension());
 
       return codec.createInputStream(fileSystem.open(inputPath));
     }
diff --git a/indexing-hadoop/src/main/java/org/apache/druid/indexer/updater/HadoopConverterJob.java b/indexing-hadoop/src/main/java/org/apache/druid/indexer/updater/HadoopConverterJob.java
index f027577c2bb..174647d25a9 100644
--- a/indexing-hadoop/src/main/java/org/apache/druid/indexer/updater/HadoopConverterJob.java
+++ b/indexing-hadoop/src/main/java/org/apache/druid/indexer/updater/HadoopConverterJob.java
@@ -141,7 +141,7 @@ public class HadoopConverterJob
 
   public static Path getJobClassPathDir(String jobName, Path workingDirectory)
   {
-    return new Path(workingDirectory, jobName.replace(":", ""));
+    return new Path(workingDirectory, StringUtils.removeChar(jobName, ':'));
   }
 
   public static void cleanup(Job job) throws IOException
diff --git a/indexing-hadoop/src/test/java/org/apache/druid/indexer/UtilsTest.java b/indexing-hadoop/src/test/java/org/apache/druid/indexer/UtilsTest.java
index 6ba39dc1a64..29e33a90793 100644
--- a/indexing-hadoop/src/test/java/org/apache/druid/indexer/UtilsTest.java
+++ b/indexing-hadoop/src/test/java/org/apache/druid/indexer/UtilsTest.java
@@ -68,7 +68,7 @@ public class UtilsTest
     @Override
     public Object apply(Object input)
     {
-      return input.toString() + DUMMY_STRING;
+      return input + DUMMY_STRING;
     }
   }
 
diff --git a/indexing-service/src/main/java/org/apache/druid/indexing/overlord/autoscaling/ec2/StringEC2UserData.java b/indexing-service/src/main/java/org/apache/druid/indexing/overlord/autoscaling/ec2/StringEC2UserData.java
index 7896ec81821..8ee0a99a62b 100644
--- a/indexing-service/src/main/java/org/apache/druid/indexing/overlord/autoscaling/ec2/StringEC2UserData.java
+++ b/indexing-service/src/main/java/org/apache/druid/indexing/overlord/autoscaling/ec2/StringEC2UserData.java
@@ -24,16 +24,20 @@ import com.fasterxml.jackson.annotation.JsonProperty;
 import org.apache.commons.codec.binary.Base64;
 import org.apache.druid.java.util.common.StringUtils;
 
+import javax.annotation.Nullable;
+import java.util.Objects;
+
 public class StringEC2UserData implements EC2UserData<StringEC2UserData>
 {
   private final String data;
+  @Nullable
   private final String versionReplacementString;
   private final String version;
 
   @JsonCreator
   public StringEC2UserData(
       @JsonProperty("data") String data,
-      @JsonProperty("versionReplacementString") String versionReplacementString,
+      @JsonProperty("versionReplacementString") @Nullable String versionReplacementString,
       @JsonProperty("version") String version
   )
   {
@@ -48,6 +52,7 @@ public class StringEC2UserData implements EC2UserData<StringEC2UserData>
     return data;
   }
 
+  @Nullable
   @JsonProperty
   public String getVersionReplacementString()
   {
@@ -71,7 +76,7 @@ public class StringEC2UserData implements EC2UserData<StringEC2UserData>
   {
     final String finalData;
     if (versionReplacementString != null && version != null) {
-      finalData = data.replace(versionReplacementString, version);
+      finalData = StringUtils.replace(data, versionReplacementString, version);
     } else {
       finalData = data;
     }
@@ -93,25 +98,16 @@ public class StringEC2UserData implements EC2UserData<StringEC2UserData>
     if (data != null ? !data.equals(that.data) : that.data != null) {
       return false;
     }
-    if (version != null ? !version.equals(that.version) : that.version != null) {
+    if (!Objects.equals(version, that.version)) {
       return false;
     }
-    if (versionReplacementString != null
-        ? !versionReplacementString.equals(that.versionReplacementString)
-        : that.versionReplacementString != null) {
-      return false;
-    }
-
-    return true;
+    return Objects.equals(versionReplacementString, that.versionReplacementString);
   }
 
   @Override
   public int hashCode()
   {
-    int result = data != null ? data.hashCode() : 0;
-    result = 31 * result + (versionReplacementString != null ? versionReplacementString.hashCode() : 0);
-    result = 31 * result + (version != null ? version.hashCode() : 0);
-    return result;
+    return Objects.hash(data, versionReplacementString, version);
   }
 
   @Override
diff --git a/indexing-service/src/main/java/org/apache/druid/indexing/overlord/http/OverlordResource.java b/indexing-service/src/main/java/org/apache/druid/indexing/overlord/http/OverlordResource.java
index 6434dfef05c..a2be927ce03 100644
--- a/indexing-service/src/main/java/org/apache/druid/indexing/overlord/http/OverlordResource.java
+++ b/indexing-service/src/main/java/org/apache/druid/indexing/overlord/http/OverlordResource.java
@@ -694,7 +694,7 @@ public class OverlordResource
     if (state == null || "complete".equals(StringUtils.toLowerCase(state))) {
       Duration duration = null;
       if (interval != null) {
-        final Interval theInterval = Intervals.of(interval.replace("_", "/"));
+        final Interval theInterval = Intervals.of(interval.replace('_', '/'));
         duration = theInterval.toDuration();
       }
       final List<TaskInfo<Task, TaskStatus>> taskInfoList =
diff --git a/indexing-service/src/test/java/org/apache/druid/indexing/common/task/MergeTaskBaseTest.java b/indexing-service/src/test/java/org/apache/druid/indexing/common/task/MergeTaskBaseTest.java
index 03275139c6a..ef14ba936bc 100644
--- a/indexing-service/src/test/java/org/apache/druid/indexing/common/task/MergeTaskBaseTest.java
+++ b/indexing-service/src/test/java/org/apache/druid/indexing/common/task/MergeTaskBaseTest.java
@@ -81,7 +81,7 @@ public class MergeTaskBaseTest
             "_2012-01-04T00:00:00.000Z_2012-01-06T00:00:00.000Z_V1_0" +
             "_2012-01-05T00:00:00.000Z_2012-01-07T00:00:00.000Z_V1_0",
             StandardCharsets.UTF_8
-        ).toString() +
+        ) +
         "_";
     Assert.assertEquals(
         desiredPrefix,
diff --git a/indexing-service/src/test/java/org/apache/druid/indexing/overlord/http/security/OverlordSecurityResourceFilterTest.java b/indexing-service/src/test/java/org/apache/druid/indexing/overlord/http/security/OverlordSecurityResourceFilterTest.java
index 0a977093f50..27dd6a38fe7 100644
--- a/indexing-service/src/test/java/org/apache/druid/indexing/overlord/http/security/OverlordSecurityResourceFilterTest.java
+++ b/indexing-service/src/test/java/org/apache/druid/indexing/overlord/http/security/OverlordSecurityResourceFilterTest.java
@@ -47,10 +47,12 @@ import org.junit.runners.Parameterized;
 
 import java.util.Collection;
 import java.util.List;
+import java.util.regex.Pattern;
 
 @RunWith(Parameterized.class)
 public class OverlordSecurityResourceFilterTest extends ResourceFilterTestHelper
 {
+  private static final Pattern WORD = Pattern.compile("\\w+");
 
   @Parameterized.Parameters(name = "{index}: requestPath={0}, requestMethod={1}, resourceFilter={2}")
   public static Collection<Object[]> data()
@@ -190,7 +192,7 @@ public class OverlordSecurityResourceFilterTest extends ResourceFilterTestHelper
   @Test
   public void testDatasourcesResourcesFilteringBadPath()
   {
-    final String badRequestPath = requestPath.replaceAll("\\w+", "droid");
+    final String badRequestPath = WORD.matcher(requestPath).replaceAll("droid");
     EasyMock.expect(request.getPath()).andReturn(badRequestPath).anyTimes();
     EasyMock.replay(req, request, authorizerMapper);
     Assert.assertFalse(((AbstractResourceFilter) resourceFilter.getRequestFilter()).isApplicable(badRequestPath));
diff --git a/integration-tests/src/main/java/org/apache/druid/testing/clients/CoordinatorResourceTestClient.java b/integration-tests/src/main/java/org/apache/druid/testing/clients/CoordinatorResourceTestClient.java
index a3a6683395b..c3145aae824 100644
--- a/integration-tests/src/main/java/org/apache/druid/testing/clients/CoordinatorResourceTestClient.java
+++ b/integration-tests/src/main/java/org/apache/druid/testing/clients/CoordinatorResourceTestClient.java
@@ -165,7 +165,8 @@ public class CoordinatorResourceTestClient
           StringUtils.format(
               "%sdatasources/%s/intervals/%s",
               getCoordinatorURL(),
-              dataSource, interval.toString().replace("/", "_")
+              dataSource,
+              interval.toString().replace('/', '_')
           )
       );
     }
diff --git a/integration-tests/src/test/java/org/apache/druid/tests/hadoop/ITHadoopIndexTest.java b/integration-tests/src/test/java/org/apache/druid/tests/hadoop/ITHadoopIndexTest.java
index 6e6b298aedf..233add803e5 100644
--- a/integration-tests/src/test/java/org/apache/druid/tests/hadoop/ITHadoopIndexTest.java
+++ b/integration-tests/src/test/java/org/apache/druid/tests/hadoop/ITHadoopIndexTest.java
@@ -21,6 +21,7 @@ package org.apache.druid.tests.hadoop;
 
 import com.google.common.base.Throwables;
 import com.google.inject.Inject;
+import org.apache.druid.java.util.common.StringUtils;
 import org.apache.druid.java.util.common.logger.Logger;
 import org.apache.druid.testing.IntegrationTestingConfig;
 import org.apache.druid.testing.guice.DruidTestModuleFactory;
@@ -65,7 +66,7 @@ public class ITHadoopIndexTest extends AbstractIndexerTest
     try {
       LOG.info("indexerFile name: [%s]", BATCH_TASK);
       indexerSpec = getTaskAsString(BATCH_TASK);
-      indexerSpec = indexerSpec.replaceAll("%%HADOOP_TEST_PATH%%", hadoopDir);
+      indexerSpec = StringUtils.replace(indexerSpec, "%%HADOOP_TEST_PATH%%", hadoopDir);
     }
     catch (Exception e) {
       LOG.error("could not read and modify indexer file: %s", e.getMessage());
diff --git a/integration-tests/src/test/java/org/apache/druid/tests/indexer/AbstractITRealtimeIndexTaskTest.java b/integration-tests/src/test/java/org/apache/druid/tests/indexer/AbstractITRealtimeIndexTaskTest.java
index 3d7802a7a47..9bf9de219ae 100644
--- a/integration-tests/src/test/java/org/apache/druid/tests/indexer/AbstractITRealtimeIndexTaskTest.java
+++ b/integration-tests/src/test/java/org/apache/druid/tests/indexer/AbstractITRealtimeIndexTaskTest.java
@@ -107,17 +107,17 @@ public abstract class AbstractITRealtimeIndexTaskTest extends AbstractIndexerTes
       }
       query_response_template = IOUtils.toString(is, "UTF-8");
 
-      String queryStr = query_response_template
-          .replace("%%TIMEBOUNDARY_RESPONSE_TIMESTAMP%%", TIMESTAMP_FMT.print(dtFirst))
-          .replace("%%TIMEBOUNDARY_RESPONSE_MAXTIME%%", TIMESTAMP_FMT.print(dtLast))
-          .replace("%%TIMEBOUNDARY_RESPONSE_MINTIME%%", TIMESTAMP_FMT.print(dtFirst))
-          .replace("%%TIMESERIES_QUERY_START%%", INTERVAL_FMT.print(dtFirst))
-          .replace("%%TIMESERIES_QUERY_END%%", INTERVAL_FMT.print(dtLast.plusMinutes(2)))
-          .replace("%%TIMESERIES_RESPONSE_TIMESTAMP%%", TIMESTAMP_FMT.print(dtFirst))
-          .replace("%%POST_AG_REQUEST_START%%", INTERVAL_FMT.print(dtFirst))
-          .replace("%%POST_AG_REQUEST_END%%", INTERVAL_FMT.print(dtLast.plusMinutes(2)))
-          .replace("%%POST_AG_RESPONSE_TIMESTAMP%%", TIMESTAMP_FMT.print(dtGroupBy.withSecondOfMinute(0))
-          );
+      String queryStr = query_response_template;
+      queryStr = StringUtils.replace(queryStr, "%%TIMEBOUNDARY_RESPONSE_TIMESTAMP%%", TIMESTAMP_FMT.print(dtFirst));
+      queryStr = StringUtils.replace(queryStr, "%%TIMEBOUNDARY_RESPONSE_MAXTIME%%", TIMESTAMP_FMT.print(dtLast));
+      queryStr = StringUtils.replace(queryStr, "%%TIMEBOUNDARY_RESPONSE_MINTIME%%", TIMESTAMP_FMT.print(dtFirst));
+      queryStr = StringUtils.replace(queryStr, "%%TIMESERIES_QUERY_START%%", INTERVAL_FMT.print(dtFirst));
+      queryStr = StringUtils.replace(queryStr, "%%TIMESERIES_QUERY_END%%", INTERVAL_FMT.print(dtLast.plusMinutes(2)));
+      queryStr = StringUtils.replace(queryStr, "%%TIMESERIES_RESPONSE_TIMESTAMP%%", TIMESTAMP_FMT.print(dtFirst));
+      queryStr = StringUtils.replace(queryStr, "%%POST_AG_REQUEST_START%%", INTERVAL_FMT.print(dtFirst));
+      queryStr = StringUtils.replace(queryStr, "%%POST_AG_REQUEST_END%%", INTERVAL_FMT.print(dtLast.plusMinutes(2)));
+      String postAgResponseTimestamp = TIMESTAMP_FMT.print(dtGroupBy.withSecondOfMinute(0));
+      queryStr = StringUtils.replace(queryStr, "%%POST_AG_RESPONSE_TIMESTAMP%%", postAgResponseTimestamp);
 
       // should hit the queries all on realtime task or some on realtime task
       // and some on historical.  Which it is depends on where in the minute we were
@@ -158,7 +158,7 @@ public abstract class AbstractITRealtimeIndexTaskTest extends AbstractIndexerTes
 
   String setShutOffTime(String taskAsString, DateTime time)
   {
-    return taskAsString.replace("#SHUTOFFTIME", time.toString());
+    return StringUtils.replace(taskAsString, "#SHUTOFFTIME", time.toString());
   }
 
   String getRouterURL()
diff --git a/integration-tests/src/test/java/org/apache/druid/tests/indexer/ITAppenderatorDriverRealtimeIndexTaskTest.java b/integration-tests/src/test/java/org/apache/druid/tests/indexer/ITAppenderatorDriverRealtimeIndexTaskTest.java
index bdd0df78ee3..54d28d9d91f 100644
--- a/integration-tests/src/test/java/org/apache/druid/tests/indexer/ITAppenderatorDriverRealtimeIndexTaskTest.java
+++ b/integration-tests/src/test/java/org/apache/druid/tests/indexer/ITAppenderatorDriverRealtimeIndexTaskTest.java
@@ -22,6 +22,7 @@ import com.google.common.base.Throwables;
 import org.apache.druid.curator.discovery.ServerDiscoverySelector;
 import org.apache.druid.java.util.common.DateTimes;
 import org.apache.druid.java.util.common.ISE;
+import org.apache.druid.java.util.common.StringUtils;
 import org.apache.druid.java.util.common.jackson.JacksonUtils;
 import org.apache.druid.java.util.common.logger.Logger;
 import org.apache.druid.testing.clients.EventReceiverFirehoseTestClient;
@@ -99,7 +100,7 @@ public class ITAppenderatorDriverRealtimeIndexTaskTest extends AbstractITRealtim
         } else if (i == 18) { // use a time 6 seconds ago so it will be out of order
           dt = dt.minusSeconds(6);
         }
-        String event = line.replace(TIME_PLACEHOLDER, EVENT_FMT.print(dt));
+        String event = StringUtils.replace(line, TIME_PLACEHOLDER, EVENT_FMT.print(dt));
         LOG.info("sending event: [%s]\n", event);
         Collection<Map<String, Object>> events = new ArrayList<Map<String, Object>>();
         events.add(this.jsonMapper.readValue(event, JacksonUtils.TYPE_REFERENCE_MAP_STRING_OBJECT));
diff --git a/integration-tests/src/test/java/org/apache/druid/tests/indexer/ITCompactionTaskTest.java b/integration-tests/src/test/java/org/apache/druid/tests/indexer/ITCompactionTaskTest.java
index 0901d39daf8..5ae32fa2b37 100644
--- a/integration-tests/src/test/java/org/apache/druid/tests/indexer/ITCompactionTaskTest.java
+++ b/integration-tests/src/test/java/org/apache/druid/tests/indexer/ITCompactionTaskTest.java
@@ -20,6 +20,7 @@
 package org.apache.druid.tests.indexer;
 
 import org.apache.druid.java.util.common.ISE;
+import org.apache.druid.java.util.common.StringUtils;
 import org.apache.druid.java.util.common.logger.Logger;
 import org.apache.druid.testing.guice.DruidTestModuleFactory;
 import org.apache.druid.testing.utils.RetryUtil;
@@ -95,7 +96,8 @@ public class ITCompactionTaskTest extends AbstractIndexerTest
   private void compactData(boolean keepSegmentGranularity) throws Exception
   {
     final String template = getTaskAsString(COMPACTION_TASK);
-    final String taskSpec = template.replace("${KEEP_SEGMENT_GRANULARITY}", Boolean.toString(keepSegmentGranularity));
+    final String taskSpec =
+        StringUtils.replace(template, "${KEEP_SEGMENT_GRANULARITY}", Boolean.toString(keepSegmentGranularity));
     final String taskID = indexer.submitTask(taskSpec);
     LOG.info("TaskID for compaction task %s", taskID);
     indexer.waitUntilTaskCompletes(taskID);
diff --git a/integration-tests/src/test/java/org/apache/druid/tests/indexer/ITKafkaIndexingServiceTest.java b/integration-tests/src/test/java/org/apache/druid/tests/indexer/ITKafkaIndexingServiceTest.java
index 4766e0f43ce..3306da96b33 100644
--- a/integration-tests/src/test/java/org/apache/druid/tests/indexer/ITKafkaIndexingServiceTest.java
+++ b/integration-tests/src/test/java/org/apache/druid/tests/indexer/ITKafkaIndexingServiceTest.java
@@ -142,10 +142,10 @@ public class ITKafkaIndexingServiceTest extends AbstractIndexerTest
       consumerProperties.put("bootstrap.servers", config.getKafkaInternalHost());
       addFilteredProperties(consumerProperties);
 
-      spec = getTaskAsString(INDEXER_FILE)
-          .replaceAll("%%DATASOURCE%%", DATASOURCE)
-          .replaceAll("%%TOPIC%%", TOPIC_NAME)
-          .replaceAll("%%CONSUMER_PROPERTIES%%", jsonMapper.writeValueAsString(consumerProperties));
+      spec = getTaskAsString(INDEXER_FILE);
+      spec = StringUtils.replace(spec, "%%DATASOURCE%%", DATASOURCE);
+      spec = StringUtils.replace(spec, "%%TOPIC%%", TOPIC_NAME);
+      spec = StringUtils.replace(spec, "%%CONSUMER_PROPERTIES%%", jsonMapper.writeValueAsString(consumerProperties));
       LOG.info("supervisorSpec: [%s]\n", spec);
     }
     catch (Exception e) {
@@ -227,16 +227,16 @@ public class ITKafkaIndexingServiceTest extends AbstractIndexerTest
       throw new ISE(e, "could not read query file: %s", QUERIES_FILE);
     }
 
-    String queryStr = query_response_template
-        .replaceAll("%%DATASOURCE%%", DATASOURCE)
-        .replace("%%TIMEBOUNDARY_RESPONSE_TIMESTAMP%%", TIMESTAMP_FMT.print(dtFirst))
-        .replace("%%TIMEBOUNDARY_RESPONSE_MAXTIME%%", TIMESTAMP_FMT.print(dtLast))
-        .replace("%%TIMEBOUNDARY_RESPONSE_MINTIME%%", TIMESTAMP_FMT.print(dtFirst))
-        .replace("%%TIMESERIES_QUERY_START%%", INTERVAL_FMT.print(dtFirst))
-        .replace("%%TIMESERIES_QUERY_END%%", INTERVAL_FMT.print(dtLast.plusMinutes(2)))
-        .replace("%%TIMESERIES_RESPONSE_TIMESTAMP%%", TIMESTAMP_FMT.print(dtFirst))
-        .replace("%%TIMESERIES_ADDED%%", Integer.toString(added))
-        .replace("%%TIMESERIES_NUMEVENTS%%", Integer.toString(num_events));
+    String queryStr = query_response_template;
+    queryStr = StringUtils.replace(queryStr, "%%DATASOURCE%%", DATASOURCE);
+    queryStr = StringUtils.replace(queryStr, "%%TIMEBOUNDARY_RESPONSE_TIMESTAMP%%", TIMESTAMP_FMT.print(dtFirst));
+    queryStr = StringUtils.replace(queryStr, "%%TIMEBOUNDARY_RESPONSE_MAXTIME%%", TIMESTAMP_FMT.print(dtLast));
+    queryStr = StringUtils.replace(queryStr, "%%TIMEBOUNDARY_RESPONSE_MINTIME%%", TIMESTAMP_FMT.print(dtFirst));
+    queryStr = StringUtils.replace(queryStr, "%%TIMESERIES_QUERY_START%%", INTERVAL_FMT.print(dtFirst));
+    queryStr = StringUtils.replace(queryStr, "%%TIMESERIES_QUERY_END%%", INTERVAL_FMT.print(dtLast.plusMinutes(2)));
+    queryStr = StringUtils.replace(queryStr, "%%TIMESERIES_RESPONSE_TIMESTAMP%%", TIMESTAMP_FMT.print(dtFirst));
+    queryStr = StringUtils.replace(queryStr, "%%TIMESERIES_ADDED%%", Integer.toString(added));
+    queryStr = StringUtils.replace(queryStr, "%%TIMESERIES_NUMEVENTS%%", Integer.toString(num_events));
 
     // this query will probably be answered from the indexing tasks but possibly from 2 historical segments / 2 indexing
     try {
diff --git a/integration-tests/src/test/java/org/apache/druid/tests/indexer/ITKafkaTest.java b/integration-tests/src/test/java/org/apache/druid/tests/indexer/ITKafkaTest.java
index 4078984e854..3388efe2867 100644
--- a/integration-tests/src/test/java/org/apache/druid/tests/indexer/ITKafkaTest.java
+++ b/integration-tests/src/test/java/org/apache/druid/tests/indexer/ITKafkaTest.java
@@ -203,11 +203,12 @@ public class ITKafkaTest extends AbstractIndexerTest
 
       addFilteredProperties(consumerProperties);
 
-      indexerSpec = getTaskAsString(INDEXER_FILE)
-          .replaceAll("%%DATASOURCE%%", DATASOURCE)
-          .replaceAll("%%TOPIC%%", TOPIC_NAME)
-          .replaceAll("%%COUNT%%", Integer.toString(num_events))
-          .replaceAll("%%CONSUMER_PROPERTIES%%", jsonMapper.writeValueAsString(consumerProperties));
+      indexerSpec = getTaskAsString(INDEXER_FILE);
+      indexerSpec = StringUtils.replace(indexerSpec, "%%DATASOURCE%%", DATASOURCE);
+      indexerSpec = StringUtils.replace(indexerSpec, "%%TOPIC%%", TOPIC_NAME);
+      indexerSpec = StringUtils.replace(indexerSpec, "%%COUNT%%", Integer.toString(num_events));
+      String consumerPropertiesJson = jsonMapper.writeValueAsString(consumerProperties);
+      indexerSpec = StringUtils.replace(indexerSpec, "%%CONSUMER_PROPERTIES%%", consumerPropertiesJson);
 
       LOG.info("indexerFile: [%s]\n", indexerSpec);
     }
@@ -261,18 +262,19 @@ public class ITKafkaTest extends AbstractIndexerTest
       throw new ISE(e, "could not read query file: %s", QUERIES_FILE);
     }
 
-    String queryStr = queryResponseTemplate
-        .replaceAll("%%DATASOURCE%%", DATASOURCE)
-        // time boundary
-        .replace("%%TIMEBOUNDARY_RESPONSE_TIMESTAMP%%", TIMESTAMP_FMT.print(dtFirst))
-        .replace("%%TIMEBOUNDARY_RESPONSE_MAXTIME%%", TIMESTAMP_FMT.print(dtLast))
-        .replace("%%TIMEBOUNDARY_RESPONSE_MINTIME%%", TIMESTAMP_FMT.print(dtFirst))
-        // time series
-        .replace("%%TIMESERIES_QUERY_START%%", INTERVAL_FMT.print(dtFirst))
-        .replace("%%TIMESERIES_QUERY_END%%", INTERVAL_FMT.print(dtFirst.plusMinutes(MINUTES_TO_SEND + 2)))
-        .replace("%%TIMESERIES_RESPONSE_TIMESTAMP%%", TIMESTAMP_FMT.print(dtFirst))
-        .replace("%%TIMESERIES_ADDED%%", Integer.toString(added))
-        .replace("%%TIMESERIES_NUMEVENTS%%", Integer.toString(num_events));
+    String queryStr = queryResponseTemplate;
+    queryStr = StringUtils.replace(queryStr, "%%DATASOURCE%%", DATASOURCE);
+    // time boundary
+    queryStr = StringUtils.replace(queryStr, "%%TIMEBOUNDARY_RESPONSE_TIMESTAMP%%", TIMESTAMP_FMT.print(dtFirst));
+    queryStr = StringUtils.replace(queryStr, "%%TIMEBOUNDARY_RESPONSE_MAXTIME%%", TIMESTAMP_FMT.print(dtLast));
+    queryStr = StringUtils.replace(queryStr, "%%TIMEBOUNDARY_RESPONSE_MINTIME%%", TIMESTAMP_FMT.print(dtFirst));
+    // time series
+    queryStr = StringUtils.replace(queryStr, "%%TIMESERIES_QUERY_START%%", INTERVAL_FMT.print(dtFirst));
+    String queryEnd = INTERVAL_FMT.print(dtFirst.plusMinutes(MINUTES_TO_SEND + 2));
+    queryStr = StringUtils.replace(queryStr, "%%TIMESERIES_QUERY_END%%", queryEnd);
+    queryStr = StringUtils.replace(queryStr, "%%TIMESERIES_RESPONSE_TIMESTAMP%%", TIMESTAMP_FMT.print(dtFirst));
+    queryStr = StringUtils.replace(queryStr, "%%TIMESERIES_ADDED%%", Integer.toString(added));
+    queryStr = StringUtils.replace(queryStr, "%%TIMESERIES_NUMEVENTS%%", Integer.toString(num_events));
 
     // this query will probably be answered from the realtime task
     try {
diff --git a/integration-tests/src/test/java/org/apache/druid/tests/indexer/ITRealtimeIndexTaskTest.java b/integration-tests/src/test/java/org/apache/druid/tests/indexer/ITRealtimeIndexTaskTest.java
index af30db33474..7dfeee13d6c 100644
--- a/integration-tests/src/test/java/org/apache/druid/tests/indexer/ITRealtimeIndexTaskTest.java
+++ b/integration-tests/src/test/java/org/apache/druid/tests/indexer/ITRealtimeIndexTaskTest.java
@@ -23,6 +23,7 @@ import com.google.common.base.Throwables;
 import org.apache.druid.curator.discovery.ServerDiscoverySelector;
 import org.apache.druid.java.util.common.DateTimes;
 import org.apache.druid.java.util.common.ISE;
+import org.apache.druid.java.util.common.StringUtils;
 import org.apache.druid.java.util.common.jackson.JacksonUtils;
 import org.apache.druid.java.util.common.logger.Logger;
 import org.apache.druid.testing.clients.EventReceiverFirehoseTestClient;
@@ -111,7 +112,7 @@ public class ITRealtimeIndexTaskTest extends AbstractITRealtimeIndexTaskTest
         } else if (i == 18) { // use a time 6 seconds ago so it will be out of order
           dt = dt.minusSeconds(6);
         }
-        String event = line.replace(TIME_PLACEHOLDER, EVENT_FMT.print(dt));
+        String event = StringUtils.replace(line, TIME_PLACEHOLDER, EVENT_FMT.print(dt));
         LOG.info("sending event: [%s]\n", event);
         Collection<Map<String, Object>> events = new ArrayList<Map<String, Object>>();
         events.add(this.jsonMapper.readValue(event, JacksonUtils.TYPE_REFERENCE_MAP_STRING_OBJECT));
diff --git a/integration-tests/src/test/java/org/apache/druid/tests/indexer/ITUnionQueryTest.java b/integration-tests/src/test/java/org/apache/druid/tests/indexer/ITUnionQueryTest.java
index 5935efb9e16..38adae8063d 100644
--- a/integration-tests/src/test/java/org/apache/druid/tests/indexer/ITUnionQueryTest.java
+++ b/integration-tests/src/test/java/org/apache/druid/tests/indexer/ITUnionQueryTest.java
@@ -157,17 +157,17 @@ public class ITUnionQueryTest extends AbstractIndexerTest
 
   private String setShutOffTime(String taskAsString, DateTime time)
   {
-    return taskAsString.replace("#SHUTOFFTIME", time.toString());
+    return StringUtils.replace(taskAsString, "#SHUTOFFTIME", time.toString());
   }
 
   private String withDataSource(String taskAsString, String dataSource)
   {
-    return taskAsString.replace(UNION_DATASOURCE, dataSource);
+    return StringUtils.replace(taskAsString, UNION_DATASOURCE, dataSource);
   }
 
   private String withServiceName(String taskAsString, String serviceName)
   {
-    return taskAsString.replace(EVENT_RECEIVER_SERVICE_PREFIX, serviceName);
+    return StringUtils.replace(taskAsString, EVENT_RECEIVER_SERVICE_PREFIX, serviceName);
   }
 
   public void postEvents(int id) throws Exception
diff --git a/pom.xml b/pom.xml
index 17a127528dd..df30dd7880a 100644
--- a/pom.xml
+++ b/pom.xml
@@ -933,7 +933,7 @@
             <plugin>
                 <groupId>de.thetaphi</groupId>
                 <artifactId>forbiddenapis</artifactId>
-                <version>2.3</version>
+                <version>2.6</version>
                 <configuration>
                     <failOnUnresolvableSignatures>false</failOnUnresolvableSignatures>
                     <bundledSignatures>
diff --git a/processing/src/main/java/org/apache/druid/collections/bitmap/WrappedConciseBitmap.java b/processing/src/main/java/org/apache/druid/collections/bitmap/WrappedConciseBitmap.java
index ee50739eb82..f0e0cfa561f 100644
--- a/processing/src/main/java/org/apache/druid/collections/bitmap/WrappedConciseBitmap.java
+++ b/processing/src/main/java/org/apache/druid/collections/bitmap/WrappedConciseBitmap.java
@@ -94,7 +94,7 @@ public class WrappedConciseBitmap implements MutableBitmap
   @Override
   public String toString()
   {
-    return getClass().getSimpleName() + bitmap.toString();
+    return getClass().getSimpleName() + bitmap;
   }
 
   @Override
diff --git a/processing/src/main/java/org/apache/druid/collections/bitmap/WrappedImmutableConciseBitmap.java b/processing/src/main/java/org/apache/druid/collections/bitmap/WrappedImmutableConciseBitmap.java
index 19d3ac39ac9..85e0a547c9f 100644
--- a/processing/src/main/java/org/apache/druid/collections/bitmap/WrappedImmutableConciseBitmap.java
+++ b/processing/src/main/java/org/apache/druid/collections/bitmap/WrappedImmutableConciseBitmap.java
@@ -67,7 +67,7 @@ public class WrappedImmutableConciseBitmap implements ImmutableBitmap
   @Override
   public String toString()
   {
-    return getClass().getSimpleName() + bitmap.toString();
+    return getClass().getSimpleName() + bitmap;
   }
 
   @Override
diff --git a/processing/src/main/java/org/apache/druid/collections/bitmap/WrappedImmutableRoaringBitmap.java b/processing/src/main/java/org/apache/druid/collections/bitmap/WrappedImmutableRoaringBitmap.java
index f689e81a721..50946ca87dd 100644
--- a/processing/src/main/java/org/apache/druid/collections/bitmap/WrappedImmutableRoaringBitmap.java
+++ b/processing/src/main/java/org/apache/druid/collections/bitmap/WrappedImmutableRoaringBitmap.java
@@ -70,7 +70,7 @@ public class WrappedImmutableRoaringBitmap implements ImmutableBitmap
   @Override
   public String toString()
   {
-    return getClass().getSimpleName() + bitmap.toString();
+    return getClass().getSimpleName() + bitmap;
   }
 
   @Override
diff --git a/processing/src/main/java/org/apache/druid/collections/bitmap/WrappedRoaringBitmap.java b/processing/src/main/java/org/apache/druid/collections/bitmap/WrappedRoaringBitmap.java
index de06d2bb871..bf20138c718 100644
--- a/processing/src/main/java/org/apache/druid/collections/bitmap/WrappedRoaringBitmap.java
+++ b/processing/src/main/java/org/apache/druid/collections/bitmap/WrappedRoaringBitmap.java
@@ -180,7 +180,7 @@ public class WrappedRoaringBitmap implements MutableBitmap
   @Override
   public String toString()
   {
-    return getClass().getSimpleName() + bitmap.toString();
+    return getClass().getSimpleName() + bitmap;
   }
 
   @Override
diff --git a/processing/src/main/java/org/apache/druid/query/extraction/CascadeExtractionFn.java b/processing/src/main/java/org/apache/druid/query/extraction/CascadeExtractionFn.java
index d03ff759625..6564eac1bce 100644
--- a/processing/src/main/java/org/apache/druid/query/extraction/CascadeExtractionFn.java
+++ b/processing/src/main/java/org/apache/druid/query/extraction/CascadeExtractionFn.java
@@ -178,8 +178,7 @@ public class CascadeExtractionFn implements ExtractionFn
   @Override
   public String toString()
   {
-    return "CascadeExtractionFn{" +
-           "extractionFns=[" + chainedExtractionFn.toString() + "]}";
+    return "CascadeExtractionFn{extractionFns=[" + chainedExtractionFn + "]}";
   }
 
   private static class ChainedExtractionFn
diff --git a/processing/src/main/java/org/apache/druid/query/monomorphicprocessing/StringRuntimeShape.java b/processing/src/main/java/org/apache/druid/query/monomorphicprocessing/StringRuntimeShape.java
index 8c695b9873c..d08dfe4a521 100644
--- a/processing/src/main/java/org/apache/druid/query/monomorphicprocessing/StringRuntimeShape.java
+++ b/processing/src/main/java/org/apache/druid/query/monomorphicprocessing/StringRuntimeShape.java
@@ -119,7 +119,7 @@ public final class StringRuntimeShape
     private void appendByteBufferShape(ByteBuffer byteBuffer)
     {
       sb.append(" {order: ");
-      sb.append(byteBuffer.order().toString());
+      sb.append(byteBuffer.order());
       sb.append('}');
     }
 
diff --git a/processing/src/main/java/org/apache/druid/query/search/BySegmentSearchResultValue.java b/processing/src/main/java/org/apache/druid/query/search/BySegmentSearchResultValue.java
index bbb3a689d05..fc5efcf5e3a 100644
--- a/processing/src/main/java/org/apache/druid/query/search/BySegmentSearchResultValue.java
+++ b/processing/src/main/java/org/apache/druid/query/search/BySegmentSearchResultValue.java
@@ -83,7 +83,7 @@ public class BySegmentSearchResultValue extends SearchResultValue
     return "BySegmentSearchResultValue{" +
            "results=" + results +
            ", segmentId='" + segmentId + '\'' +
-           ", interval='" + interval.toString() + '\'' +
+           ", interval='" + interval + '\'' +
            '}';
   }
 }
diff --git a/processing/src/main/java/org/apache/druid/query/topn/BySegmentTopNResultValue.java b/processing/src/main/java/org/apache/druid/query/topn/BySegmentTopNResultValue.java
index 0d825076dcb..cc426101241 100644
--- a/processing/src/main/java/org/apache/druid/query/topn/BySegmentTopNResultValue.java
+++ b/processing/src/main/java/org/apache/druid/query/topn/BySegmentTopNResultValue.java
@@ -85,7 +85,7 @@ public class BySegmentTopNResultValue extends TopNResultValue implements BySegme
     return "BySegmentTopNResultValue{" +
            "results=" + results +
            ", segmentId='" + segmentId + '\'' +
-           ", interval='" + interval.toString() + '\'' +
+           ", interval='" + interval + '\'' +
            '}';
   }
 }
diff --git a/processing/src/test/java/org/apache/druid/collections/bitmap/BitmapBenchmark.java b/processing/src/test/java/org/apache/druid/collections/bitmap/BitmapBenchmark.java
index 81874b58d3a..e7c3fba9f1b 100644
--- a/processing/src/test/java/org/apache/druid/collections/bitmap/BitmapBenchmark.java
+++ b/processing/src/test/java/org/apache/druid/collections/bitmap/BitmapBenchmark.java
@@ -100,9 +100,9 @@ public class BitmapBenchmark
 
   protected static void printSizeStats(double density, String name)
   {
-    System.out.println("");
+    System.out.println();
     System.out.println("## " + name);
-    System.out.println("");
+    System.out.println();
     System.out.printf(Locale.ENGLISH, " d = %06.5f | Concise | Roaring%n", density);
     System.out.println("-------------|---------|---------");
     System.out.printf(Locale.ENGLISH, "Count        |   %5d |   %5d %n", conciseCount, roaringCount);
diff --git a/processing/src/test/java/org/apache/druid/segment/filter/BaseFilterTest.java b/processing/src/test/java/org/apache/druid/segment/filter/BaseFilterTest.java
index 100adf053ae..9200ec48b92 100644
--- a/processing/src/test/java/org/apache/druid/segment/filter/BaseFilterTest.java
+++ b/processing/src/test/java/org/apache/druid/segment/filter/BaseFilterTest.java
@@ -414,22 +414,22 @@ public abstract class BaseFilterTest
   )
   {
     Assert.assertEquals(
-        "Cursor: " + filter.toString(),
+        "Cursor: " + filter,
         expectedRows,
         selectColumnValuesMatchingFilter(filter, "dim0")
     );
     Assert.assertEquals(
-        "Cursor with postFiltering: " + filter.toString(),
+        "Cursor with postFiltering: " + filter,
         expectedRows,
         selectColumnValuesMatchingFilterUsingPostFiltering(filter, "dim0")
     );
     Assert.assertEquals(
-        "Filtered aggregator: " + filter.toString(),
+        "Filtered aggregator: " + filter,
         expectedRows.size(),
         selectCountUsingFilteredAggregator(filter)
     );
     Assert.assertEquals(
-        "RowBasedColumnSelectorFactory: " + filter.toString(),
+        "RowBasedColumnSelectorFactory: " + filter,
         expectedRows,
         selectColumnValuesMatchingFilterUsingRowBasedColumnSelectorFactory(filter, "dim0")
     );
diff --git a/server/src/main/java/org/apache/druid/client/coordinator/CoordinatorClient.java b/server/src/main/java/org/apache/druid/client/coordinator/CoordinatorClient.java
index 0450af4b8f3..4f59d87a849 100644
--- a/server/src/main/java/org/apache/druid/client/coordinator/CoordinatorClient.java
+++ b/server/src/main/java/org/apache/druid/client/coordinator/CoordinatorClient.java
@@ -58,7 +58,7 @@ public class CoordinatorClient
                                         StringUtils.format(
                                            "/druid/coordinator/v1/datasources/%s/intervals/%s/serverview?partial=%s",
                                            dataSource,
-                                           interval.toString().replace("/", "_"),
+                                           interval.toString().replace('/', '_'),
                                            incompleteOk
                                        ))
       );
diff --git a/server/src/main/java/org/apache/druid/curator/discovery/CuratorServiceUtils.java b/server/src/main/java/org/apache/druid/curator/discovery/CuratorServiceUtils.java
index 60c51e304c9..1513d9fc05d 100644
--- a/server/src/main/java/org/apache/druid/curator/discovery/CuratorServiceUtils.java
+++ b/server/src/main/java/org/apache/druid/curator/discovery/CuratorServiceUtils.java
@@ -42,6 +42,6 @@ public class CuratorServiceUtils
    */
   protected static String makeCanonicalServiceName(String serviceName)
   {
-    return serviceName.replaceAll("/", ":");
+    return serviceName.replace('/', ':');
   }
 }
diff --git a/server/src/main/java/org/apache/druid/segment/loading/LocalDataSegmentPusher.java b/server/src/main/java/org/apache/druid/segment/loading/LocalDataSegmentPusher.java
index 68913504a8a..bdddfaf080d 100644
--- a/server/src/main/java/org/apache/druid/segment/loading/LocalDataSegmentPusher.java
+++ b/server/src/main/java/org/apache/druid/segment/loading/LocalDataSegmentPusher.java
@@ -135,7 +135,7 @@ public class LocalDataSegmentPusher implements DataSegmentPusher
 
   private String makeIntermediateDir()
   {
-    return "intermediate_pushes/" + UUID.randomUUID().toString();
+    return "intermediate_pushes/" + UUID.randomUUID();
   }
 
   private long compressSegment(File dataSegmentFile, File dest) throws IOException
diff --git a/server/src/main/java/org/apache/druid/segment/realtime/firehose/EventReceiverFirehoseFactory.java b/server/src/main/java/org/apache/druid/segment/realtime/firehose/EventReceiverFirehoseFactory.java
index 94e2c6cd50b..3abf0c4dcbf 100644
--- a/server/src/main/java/org/apache/druid/segment/realtime/firehose/EventReceiverFirehoseFactory.java
+++ b/server/src/main/java/org/apache/druid/segment/realtime/firehose/EventReceiverFirehoseFactory.java
@@ -138,8 +138,9 @@ public class EventReceiverFirehoseFactory implements FirehoseFactory<InputRowPar
     if (chatHandlerProvider.isPresent()) {
       log.info("Found chathandler of class[%s]", chatHandlerProvider.get().getClass().getName());
       chatHandlerProvider.get().register(serviceName, firehose);
-      if (serviceName.contains(":")) {
-        chatHandlerProvider.get().register(serviceName.replaceAll(".*:", ""), firehose); // rofl
+      int lastIndexOfColon = serviceName.lastIndexOf(':');
+      if (lastIndexOfColon > 0) {
+        chatHandlerProvider.get().register(serviceName.substring(lastIndexOfColon + 1), firehose);
       }
     } else {
       log.warn("No chathandler detected");
diff --git a/server/src/main/java/org/apache/druid/segment/realtime/plumber/RealtimePlumber.java b/server/src/main/java/org/apache/druid/segment/realtime/plumber/RealtimePlumber.java
index 8d80f609cb2..b0453d90c38 100644
--- a/server/src/main/java/org/apache/druid/segment/realtime/plumber/RealtimePlumber.java
+++ b/server/src/main/java/org/apache/druid/segment/realtime/plumber/RealtimePlumber.java
@@ -625,7 +625,7 @@ public class RealtimePlumber implements Plumber
     Object metadata = null;
     long latestCommitTime = 0;
     for (File sinkDir : files) {
-      final Interval sinkInterval = Intervals.of(sinkDir.getName().replace("_", "/"));
+      final Interval sinkInterval = Intervals.of(sinkDir.getName().replace('_', '/'));
 
       //final File[] sinkFiles = sinkDir.listFiles();
       // To avoid reading and listing of "merged" dir
@@ -921,14 +921,17 @@ public class RealtimePlumber implements Plumber
   protected File computeCorruptedFileDumpDir(File persistDir, DataSchema schema)
   {
     return new File(
-        persistDir.getAbsolutePath()
-                  .replace(schema.getDataSource(), "corrupted" + File.pathSeparator + schema.getDataSource())
+        StringUtils.replace(
+            persistDir.getAbsolutePath(),
+            schema.getDataSource(),
+            "corrupted" + File.pathSeparator + schema.getDataSource()
+        )
     );
   }
 
   protected File computePersistDir(DataSchema schema, Interval interval)
   {
-    return new File(computeBaseDir(schema), interval.toString().replace("/", "_"));
+    return new File(computeBaseDir(schema), interval.toString().replace('/', '_'));
   }
 
   /**
diff --git a/server/src/main/java/org/apache/druid/server/coordination/ServerType.java b/server/src/main/java/org/apache/druid/server/coordination/ServerType.java
index 240cee64904..d1b7fd1204f 100644
--- a/server/src/main/java/org/apache/druid/server/coordination/ServerType.java
+++ b/server/src/main/java/org/apache/druid/server/coordination/ServerType.java
@@ -86,13 +86,13 @@ public enum ServerType
   @JsonCreator
   public static ServerType fromString(String type)
   {
-    return ServerType.valueOf(StringUtils.toUpperCase(type).replace("-", "_"));
+    return ServerType.valueOf(StringUtils.toUpperCase(type).replace('-', '_'));
   }
 
   @Override
   @JsonValue
   public String toString()
   {
-    return StringUtils.toLowerCase(name()).replace("_", "-");
+    return StringUtils.toLowerCase(name()).replace('_', '-');
   }
 }
diff --git a/server/src/main/java/org/apache/druid/server/http/DatasourcesResource.java b/server/src/main/java/org/apache/druid/server/http/DatasourcesResource.java
index 77ca931eae1..450dbd4af08 100644
--- a/server/src/main/java/org/apache/druid/server/http/DatasourcesResource.java
+++ b/server/src/main/java/org/apache/druid/server/http/DatasourcesResource.java
@@ -243,7 +243,7 @@ public class DatasourcesResource
     if (indexingServiceClient == null) {
       return Response.ok(ImmutableMap.of("error", "no indexing service found")).build();
     }
-    final Interval theInterval = Intervals.of(interval.replace("_", "/"));
+    final Interval theInterval = Intervals.of(interval.replace('_', '/'));
     try {
       indexingServiceClient.killSegments(dataSourceName, theInterval);
     }
@@ -336,7 +336,7 @@ public class DatasourcesResource
   )
   {
     final ImmutableDruidDataSource dataSource = getDataSource(dataSourceName);
-    final Interval theInterval = Intervals.of(interval.replace("_", "/"));
+    final Interval theInterval = Intervals.of(interval.replace('_', '/'));
 
     if (dataSource == null) {
       return Response.noContent().build();
@@ -629,7 +629,7 @@ public class DatasourcesResource
     TimelineLookup<String, SegmentLoadInfo> timeline = serverInventoryView.getTimeline(
         new TableDataSource(dataSourceName)
     );
-    final Interval theInterval = Intervals.of(interval.replace("_", "/"));
+    final Interval theInterval = Intervals.of(interval.replace('_', '/'));
     if (timeline == null) {
       log.debug("No timeline found for datasource[%s]", dataSourceName);
       return Response.ok(new ArrayList<ImmutableSegmentLoadInfo>()).build();
diff --git a/server/src/main/java/org/apache/druid/server/http/IntervalsResource.java b/server/src/main/java/org/apache/druid/server/http/IntervalsResource.java
index 56357944c5f..957075ae6e9 100644
--- a/server/src/main/java/org/apache/druid/server/http/IntervalsResource.java
+++ b/server/src/main/java/org/apache/druid/server/http/IntervalsResource.java
@@ -98,7 +98,7 @@ public class IntervalsResource
       @Context final HttpServletRequest req
   )
   {
-    final Interval theInterval = Intervals.of(interval.replace("_", "/"));
+    final Interval theInterval = Intervals.of(interval.replace('_', '/'));
     final Set<ImmutableDruidDataSource> datasources = InventoryViewUtils.getSecuredDataSources(
         req,
         serverInventoryView,
diff --git a/server/src/main/java/org/apache/druid/server/metrics/MonitorsConfig.java b/server/src/main/java/org/apache/druid/server/metrics/MonitorsConfig.java
index 71300704ce4..9d9241b7d40 100644
--- a/server/src/main/java/org/apache/druid/server/metrics/MonitorsConfig.java
+++ b/server/src/main/java/org/apache/druid/server/metrics/MonitorsConfig.java
@@ -21,6 +21,7 @@ package org.apache.druid.server.metrics;
 
 import com.fasterxml.jackson.annotation.JsonProperty;
 import com.google.common.collect.ImmutableMap;
+import org.apache.druid.java.util.common.StringUtils;
 import org.apache.druid.java.util.common.logger.Logger;
 import org.apache.druid.java.util.metrics.Monitor;
 import org.apache.druid.query.DruidMetrics;
@@ -115,9 +116,11 @@ public class MonitorsConfig
     }
     try {
       for (String monitorName : monitorNames) {
-        String effectiveMonitorName = monitorName
-            .replace(METAMX_PACKAGE, APACHE_DRUID_PACKAGE_NAME)
-            .replace(IO_DRUID_PACKAGE, APACHE_DRUID_PACKAGE_NAME);
+        final String effectiveMonitorName = StringUtils.replace(
+            StringUtils.replace(monitorName, METAMX_PACKAGE, APACHE_DRUID_PACKAGE_NAME),
+            IO_DRUID_PACKAGE,
+            APACHE_DRUID_PACKAGE_NAME
+        );
         if (!effectiveMonitorName.equals(monitorName)) {
           log.warn(
               "Deprecated Monitor class name[%s] found, please use name[%s] instead.",
diff --git a/server/src/test/java/org/apache/druid/curator/CuratorTestBase.java b/server/src/test/java/org/apache/druid/curator/CuratorTestBase.java
index bf080871587..40a039a09b7 100644
--- a/server/src/test/java/org/apache/druid/curator/CuratorTestBase.java
+++ b/server/src/test/java/org/apache/druid/curator/CuratorTestBase.java
@@ -146,7 +146,7 @@ public class CuratorTestBase
           druidServer.getType().toString(),
           druidServer.getTier(),
           DateTimes.nowUtc().toString()
-        ) + String.valueOf(batchCtr++)
+        ) + (batchCtr++)
     );
 
 
diff --git a/server/src/test/java/org/apache/druid/curator/discovery/ServiceAnnouncerTest.java b/server/src/test/java/org/apache/druid/curator/discovery/ServiceAnnouncerTest.java
index 1aa8e17956f..57f7517239d 100644
--- a/server/src/test/java/org/apache/druid/curator/discovery/ServiceAnnouncerTest.java
+++ b/server/src/test/java/org/apache/druid/curator/discovery/ServiceAnnouncerTest.java
@@ -62,7 +62,7 @@ public class ServiceAnnouncerTest extends CuratorTestBase
               public boolean apply(String input)
               {
                 try {
-                  return serviceDiscovery.queryForInstances(input.replaceAll("/", ":")).size() == 1;
+                  return serviceDiscovery.queryForInstances(input.replace('/', ':')).size() == 1;
                 }
                 catch (Exception e) {
                   throw new ISE(
diff --git a/server/src/test/java/org/apache/druid/metadata/TestDerbyConnector.java b/server/src/test/java/org/apache/druid/metadata/TestDerbyConnector.java
index 199720b25bd..e5460ce402b 100644
--- a/server/src/test/java/org/apache/druid/metadata/TestDerbyConnector.java
+++ b/server/src/test/java/org/apache/druid/metadata/TestDerbyConnector.java
@@ -67,7 +67,7 @@ public class TestDerbyConnector extends DerbyConnector
 
   public static String dbSafeUUID()
   {
-    return UUID.randomUUID().toString().replace("-", "");
+    return StringUtils.removeChar(UUID.randomUUID().toString(), '-');
   }
 
   public String getJdbcUri()
diff --git a/server/src/test/java/org/apache/druid/segment/loading/LocalDataSegmentPusherTest.java b/server/src/test/java/org/apache/druid/segment/loading/LocalDataSegmentPusherTest.java
index 9d79c0779c6..6bfca906ddc 100644
--- a/server/src/test/java/org/apache/druid/segment/loading/LocalDataSegmentPusherTest.java
+++ b/server/src/test/java/org/apache/druid/segment/loading/LocalDataSegmentPusherTest.java
@@ -39,6 +39,7 @@ import org.junit.rules.TemporaryFolder;
 
 import java.io.File;
 import java.io.IOException;
+import java.util.regex.Pattern;
 
 public class LocalDataSegmentPusherTest
 {
@@ -124,8 +125,10 @@ public class LocalDataSegmentPusherTest
     DataSegment segment = localDataSegmentPusher.push(dataSegmentFiles, dataSegment, true);
 
     String path = segment.getLoadSpec().get("path").toString();
-    String matcher = ".*/ds/1970-01-01T00:00:00\\.000Z_1970-01-01T00:00:00\\.001Z/v1/0/[A-Za-z0-9-]{36}/index\\.zip";
-    Assert.assertTrue(path, path.matches(matcher));
+    Pattern pattern = Pattern.compile(
+        ".*/ds/1970-01-01T00:00:00\\.000Z_1970-01-01T00:00:00\\.001Z/v1/0/[A-Za-z0-9-]{36}/index\\.zip"
+    );
+    Assert.assertTrue(path, pattern.matcher(path).matches());
     Assert.assertTrue(new File(path).exists());
   }
 
diff --git a/server/src/test/java/org/apache/druid/server/AsyncQueryForwardingServletTest.java b/server/src/test/java/org/apache/druid/server/AsyncQueryForwardingServletTest.java
index 262ad92df7b..e86ac19a302 100644
--- a/server/src/test/java/org/apache/druid/server/AsyncQueryForwardingServletTest.java
+++ b/server/src/test/java/org/apache/druid/server/AsyncQueryForwardingServletTest.java
@@ -39,6 +39,7 @@ import org.apache.druid.guice.annotations.Self;
 import org.apache.druid.guice.annotations.Smile;
 import org.apache.druid.guice.http.DruidHttpClientConfig;
 import org.apache.druid.initialization.Initialization;
+import org.apache.druid.java.util.common.StringUtils;
 import org.apache.druid.java.util.common.granularity.Granularities;
 import org.apache.druid.java.util.common.lifecycle.Lifecycle;
 import org.apache.druid.query.DefaultGenericQueryMetricsFactory;
@@ -350,11 +351,11 @@ public class AsyncQueryForwardingServletTest extends BaseJettyTest
             @Override
             protected String rewriteURI(HttpServletRequest request, String scheme, String host)
             {
-              String uri = super.rewriteURI(request, scheme, host).toString();
+              String uri = super.rewriteURI(request, scheme, host);
               if (uri.contains("/druid/v2")) {
-                return URI.create(uri.replace("/druid/v2", "/default")).toString();
+                return URI.create(StringUtils.replace(uri, "/druid/v2", "/default")).toString();
               }
-              return URI.create(uri.replace("/proxy", "")).toString();
+              return URI.create(StringUtils.replace(uri, "/proxy", "")).toString();
             }
           });
       //NOTE: explicit maxThreads to workaround https://tickets.puppetlabs.com/browse/TK-152
diff --git a/server/src/test/java/org/apache/druid/server/http/DatasourcesResourceTest.java b/server/src/test/java/org/apache/druid/server/http/DatasourcesResourceTest.java
index da95b0baa58..d42b6783f5d 100644
--- a/server/src/test/java/org/apache/druid/server/http/DatasourcesResourceTest.java
+++ b/server/src/test/java/org/apache/druid/server/http/DatasourcesResourceTest.java
@@ -538,7 +538,7 @@ public class DatasourcesResourceTest
   public void testDeleteDataSourceSpecificInterval()
   {
     String interval = "2010-01-01_P1D";
-    Interval theInterval = Intervals.of(interval.replace("_", "/"));
+    Interval theInterval = Intervals.of(interval.replace('_', '/'));
 
     IndexingServiceClient indexingServiceClient = EasyMock.createStrictMock(IndexingServiceClient.class);
     indexingServiceClient.killSegments("datasource1", theInterval);
diff --git a/server/src/test/java/org/apache/druid/server/http/security/SecurityResourceFilterTest.java b/server/src/test/java/org/apache/druid/server/http/security/SecurityResourceFilterTest.java
index be85f255cd7..a4c4156560d 100644
--- a/server/src/test/java/org/apache/druid/server/http/security/SecurityResourceFilterTest.java
+++ b/server/src/test/java/org/apache/druid/server/http/security/SecurityResourceFilterTest.java
@@ -46,10 +46,13 @@ import org.junit.runner.RunWith;
 import org.junit.runners.Parameterized;
 
 import java.util.Collection;
+import java.util.regex.Pattern;
 
 @RunWith(Parameterized.class)
 public class SecurityResourceFilterTest extends ResourceFilterTestHelper
 {
+  private static final Pattern WORD = Pattern.compile("\\w+");
+
   @Parameterized.Parameters
   public static Collection<Object[]> data()
   {
@@ -127,7 +130,7 @@ public class SecurityResourceFilterTest extends ResourceFilterTestHelper
   public void testResourcesFilteringBadPath()
   {
     EasyMock.replay(req, request, authorizerMapper);
-    final String badRequestPath = requestPath.replaceAll("\\w+", "droid");
+    final String badRequestPath = WORD.matcher(requestPath).replaceAll("droid");
     Assert.assertFalse(((AbstractResourceFilter) resourceFilter.getRequestFilter()).isApplicable(badRequestPath));
     EasyMock.verify(req, request, authorizerMapper);
   }
diff --git a/server/src/test/java/org/apache/druid/server/log/FileRequestLoggerTest.java b/server/src/test/java/org/apache/druid/server/log/FileRequestLoggerTest.java
index 060412cc882..6163fd3ba7f 100644
--- a/server/src/test/java/org/apache/druid/server/log/FileRequestLoggerTest.java
+++ b/server/src/test/java/org/apache/druid/server/log/FileRequestLoggerTest.java
@@ -49,7 +49,7 @@ public class FileRequestLoggerTest
     ObjectMapper objectMapper = new ObjectMapper();
     DateTime dateTime = DateTimes.nowUtc();
     File logDir = temporaryFolder.newFolder();
-    String actualLogString = dateTime.toString() + "\t" + HOST;
+    String actualLogString = dateTime + "\t" + HOST;
 
     FileRequestLogger fileRequestLogger = new FileRequestLogger(objectMapper, scheduler, logDir);
     fileRequestLogger.start();
diff --git a/services/src/main/java/org/apache/druid/cli/convert/PrefixRename.java b/services/src/main/java/org/apache/druid/cli/convert/PrefixRename.java
deleted file mode 100644
index 866e3b86f08..00000000000
--- a/services/src/main/java/org/apache/druid/cli/convert/PrefixRename.java
+++ /dev/null
@@ -1,69 +0,0 @@
-/*
- * Licensed to the Apache Software Foundation (ASF) under one
- * or more contributor license agreements.  See the NOTICE file
- * distributed with this work for additional information
- * regarding copyright ownership.  The ASF licenses this file
- * to you under the Apache License, Version 2.0 (the
- * "License"); you may not use this file except in compliance
- * with the License.  You may obtain a copy of the License at
- *
- *   http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing,
- * software distributed under the License is distributed on an
- * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
- * KIND, either express or implied.  See the License for the
- * specific language governing permissions and limitations
- * under the License.
- */
-
-package org.apache.druid.cli.convert;
-
-import com.google.common.collect.ImmutableMap;
-import com.google.common.collect.Maps;
-
-import java.util.Map;
-import java.util.Properties;
-import java.util.concurrent.atomic.AtomicBoolean;
-
-/**
- */
-public class PrefixRename implements PropertyConverter
-{
-  private final String prefix;
-  private final String outputPrefix;
-
-  private final AtomicBoolean ran = new AtomicBoolean(false);
-
-  public PrefixRename(
-      String prefix,
-      String outputPrefix
-  )
-  {
-    this.prefix = prefix;
-    this.outputPrefix = outputPrefix;
-  }
-
-  @Override
-  public boolean canHandle(String property)
-  {
-    return property.startsWith(prefix) && !ran.get();
-  }
-
-  @Override
-  public Map<String, String> convert(Properties properties)
-  {
-    if (!ran.getAndSet(true)) {
-      Map<String, String> retVal = Maps.newLinkedHashMap();
-
-      for (String property : properties.stringPropertyNames()) {
-        if (property.startsWith(prefix)) {
-          retVal.put(property.replace(prefix, outputPrefix), properties.getProperty(property));
-        }
-      }
-
-      return retVal;
-    }
-    return ImmutableMap.of();
-  }
-}
diff --git a/sql/src/main/java/org/apache/druid/sql/avatica/AvaticaMonitor.java b/sql/src/main/java/org/apache/druid/sql/avatica/AvaticaMonitor.java
index 369d6a5409e..45befef6325 100644
--- a/sql/src/main/java/org/apache/druid/sql/avatica/AvaticaMonitor.java
+++ b/sql/src/main/java/org/apache/druid/sql/avatica/AvaticaMonitor.java
@@ -25,6 +25,7 @@ import org.apache.calcite.avatica.metrics.Histogram;
 import org.apache.calcite.avatica.metrics.Meter;
 import org.apache.calcite.avatica.metrics.MetricsSystem;
 import org.apache.calcite.avatica.metrics.Timer;
+import org.apache.druid.java.util.common.StringUtils;
 import org.apache.druid.java.util.common.logger.Logger;
 import org.apache.druid.java.util.emitter.service.ServiceEmitter;
 import org.apache.druid.java.util.emitter.service.ServiceMetricEvent;
@@ -178,6 +179,6 @@ public class AvaticaMonitor extends AbstractMonitor implements MetricsSystem
 
   private String fullMetricName(final String name)
   {
-    return name.replace("org.apache.calcite.avatica", "avatica").replace(".", "/");
+    return StringUtils.replace(name, "org.apache.calcite.avatica", "avatica").replace('.', '/');
   }
 }
diff --git a/sql/src/main/java/org/apache/druid/sql/calcite/planner/Calcites.java b/sql/src/main/java/org/apache/druid/sql/calcite/planner/Calcites.java
index 3601e15b66e..c251d31ee6d 100644
--- a/sql/src/main/java/org/apache/druid/sql/calcite/planner/Calcites.java
+++ b/sql/src/main/java/org/apache/druid/sql/calcite/planner/Calcites.java
@@ -56,6 +56,7 @@ import org.joda.time.format.ISODateTimeFormat;
 
 import java.nio.charset.Charset;
 import java.util.NavigableSet;
+import java.util.regex.Pattern;
 
 /**
  * Utility functions for Calcite.
@@ -77,6 +78,8 @@ public class Calcites
 
   private static final Charset DEFAULT_CHARSET = Charset.forName(ConversionUtil.NATIVE_UTF16_CHARSET_NAME);
 
+  private static final Pattern TRAILING_ZEROS = Pattern.compile("\\.?0+$");
+
   private Calcites()
   {
     // No instantiation.
@@ -129,7 +132,7 @@ public class Calcites
       }
     }
     builder.append("'");
-    return isPlainAscii ? builder.toString() : "U&" + builder.toString();
+    return isPlainAscii ? builder.toString() : "U&" + builder;
 
   }
 
@@ -248,7 +251,10 @@ public class Calcites
   public static TimestampString jodaToCalciteTimestampString(final DateTime dateTime, final DateTimeZone timeZone)
   {
     // The replaceAll is because Calcite doesn't like trailing zeroes in its fractional seconds part.
-    return new TimestampString(CALCITE_TIMESTAMP_PRINTER.print(dateTime.withZone(timeZone)).replaceAll("\\.?0+$", ""));
+    String timestampString = TRAILING_ZEROS
+        .matcher(CALCITE_TIMESTAMP_PRINTER.print(dateTime.withZone(timeZone)))
+        .replaceAll("");
+    return new TimestampString(timestampString);
   }
 
   /**
@@ -262,7 +268,10 @@ public class Calcites
   public static TimeString jodaToCalciteTimeString(final DateTime dateTime, final DateTimeZone timeZone)
   {
     // The replaceAll is because Calcite doesn't like trailing zeroes in its fractional seconds part.
-    return new TimeString(CALCITE_TIME_PRINTER.print(dateTime.withZone(timeZone)).replaceAll("\\.?0+$", ""));
+    String timeString = TRAILING_ZEROS
+        .matcher(CALCITE_TIME_PRINTER.print(dateTime.withZone(timeZone)))
+        .replaceAll("");
+    return new TimeString(timeString);
   }
 
   /**
diff --git a/sql/src/main/java/org/apache/druid/sql/calcite/schema/SystemSchema.java b/sql/src/main/java/org/apache/druid/sql/calcite/schema/SystemSchema.java
index 1fa23884774..ae8ba9460fa 100644
--- a/sql/src/main/java/org/apache/druid/sql/calcite/schema/SystemSchema.java
+++ b/sql/src/main/java/org/apache/druid/sql/calcite/schema/SystemSchema.java
@@ -465,7 +465,7 @@ public class SystemSchema extends AbstractSchema
           authorizerMapper
       );
       if (!access.isAllowed()) {
-        throw new ForbiddenException("Insufficient permission to view servers :" + access.toString());
+        throw new ForbiddenException("Insufficient permission to view servers :" + access);
       }
       final FluentIterable<Object[]> results = FluentIterable
           .from(druidServers)
diff --git a/sql/src/test/java/org/apache/druid/sql/calcite/expression/ExpressionsTest.java b/sql/src/test/java/org/apache/druid/sql/calcite/expression/ExpressionsTest.java
index d64b9a00752..1dc8a5cab2b 100644
--- a/sql/src/test/java/org/apache/druid/sql/calcite/expression/ExpressionsTest.java
+++ b/sql/src/test/java/org/apache/druid/sql/calcite/expression/ExpressionsTest.java
@@ -819,10 +819,10 @@ public class ExpressionsTest extends CalciteTestBase
   )
   {
     final DruidExpression expression = Expressions.toDruidExpression(plannerContext, rowSignature, rexNode);
-    Assert.assertEquals("Expression for: " + rexNode.toString(), expectedExpression, expression);
+    Assert.assertEquals("Expression for: " + rexNode, expectedExpression, expression);
 
     final ExprEval result = Parser.parse(expression.getExpression(), plannerContext.getExprMacroTable())
                                   .eval(Parser.withMap(bindings));
-    Assert.assertEquals("Result for: " + rexNode.toString(), expectedResult, result.value());
+    Assert.assertEquals("Result for: " + rexNode, expectedResult, result.value());
   }
 }