Merge remote-tracking branch 'upstream/master' into BAEL_4302

algorithms-miscellaneous-6/README.md

@@ -7,4 +7,6 @@
 - [Efficiently Merge Sorted Java Sequences](https://www.baeldung.com/java-merge-sorted-sequences)
 - [Introduction to Greedy Algorithms with Java](https://www.baeldung.com/java-greedy-algorithms)
 - [The Caesar Cipher in Java](https://www.baeldung.com/java-caesar-cipher)
+- [Implementing a 2048 Solver in Java](https://www.baeldung.com/2048-java-solver)
+- [Finding Top K Elements in an Array](https://www.baeldung.com/java-array-top-elements)
 - More articles: [[<-- prev]](/../algorithms-miscellaneous-5)

algorithms-miscellaneous-6/src/main/java/com/baeldung/algorithms/topkelements/BruteForceTopKElementsFinder.java

@@ -0,0 +1,26 @@
+package com.baeldung.algorithms.topkelements;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class BruteForceTopKElementsFinder implements TopKElementsFinder<Integer> {
+
+    public List<Integer> findTopK(List<Integer> input, int k) {
+        List<Integer> array = new ArrayList<>(input);
+        List<Integer> topKList = new ArrayList<>();
+
+        for (int i = 0; i < k; i++) {
+            int maxIndex = 0;
+
+            for (int j = 1; j < array.size(); j++) {
+                if (array.get(j) > array.get(maxIndex)) {
+                    maxIndex = j;
+                }
+            }
+
+            topKList.add(array.remove(maxIndex));
+        }
+
+        return topKList;
+    }
+}

algorithms-miscellaneous-6/src/main/java/com/baeldung/algorithms/topkelements/MaxHeapTopKElementsFinder.java

@@ -0,0 +1,26 @@
+package com.baeldung.algorithms.topkelements;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+import java.util.PriorityQueue;
+
+public class MaxHeapTopKElementsFinder implements TopKElementsFinder<Integer> {
+
+    public List<Integer> findTopK(List<Integer> input, int k) {
+        PriorityQueue<Integer> maxHeap = new PriorityQueue<>();
+
+        input.forEach(number -> {
+            maxHeap.add(number);
+
+            if (maxHeap.size() > k) {
+                maxHeap.poll();
+            }
+        });
+
+        List<Integer> topKList = new ArrayList<>(maxHeap);
+        Collections.reverse(topKList);
+
+        return topKList;
+    }
+}

algorithms-miscellaneous-6/src/main/java/com/baeldung/algorithms/topkelements/TopKElementsFinder.java

@@ -0,0 +1,7 @@
+package com.baeldung.algorithms.topkelements;
+
+import java.util.List;
+
+public interface TopKElementsFinder<T extends Comparable<T>> {
+    List<T> findTopK(List<T> input, int k);
+}

algorithms-miscellaneous-6/src/main/java/com/baeldung/algorithms/topkelements/TreeSetTopKElementsFinder.java

@@ -0,0 +1,17 @@
+package com.baeldung.algorithms.topkelements;
+
+import java.util.Comparator;
+import java.util.List;
+import java.util.Set;
+import java.util.TreeSet;
+import java.util.stream.Collectors;
+
+public class TreeSetTopKElementsFinder implements TopKElementsFinder<Integer> {
+
+    public List<Integer> findTopK(List<Integer> input, int k) {
+        Set<Integer> sortedSet = new TreeSet<>(Comparator.reverseOrder());
+        sortedSet.addAll(input);
+
+        return sortedSet.stream().limit(k).collect(Collectors.toList());
+    }
+}

algorithms-miscellaneous-6/src/test/java/com/baeldung/algorithms/topkelements/TopKElementsFinderUnitTest.java

@@ -0,0 +1,46 @@
+package com.baeldung.algorithms.topkelements;
+
+import org.junit.Test;
+
+import java.util.Arrays;
+import java.util.List;
+
+import static org.assertj.core.api.Java6Assertions.assertThat;
+
+public class TopKElementsFinderUnitTest {
+    private final TopKElementsFinder<Integer> bruteForceFinder = new BruteForceTopKElementsFinder();
+    private final TopKElementsFinder<Integer> maxHeapFinder = new MaxHeapTopKElementsFinder();
+    private final TopKElementsFinder<Integer> treeSetFinder = new TreeSetTopKElementsFinder();
+
+    private final int k = 4;
+    private final List<Integer> distinctIntegers = Arrays.asList(1, 2, 3, 9, 7, 6, 12);
+    private final List<Integer> distinctIntegersTopK = Arrays.asList(9, 7, 6, 12);
+    private final List<Integer> nonDistinctIntegers = Arrays.asList(1, 2, 3, 3, 9, 9, 7, 6, 12);
+    private final List<Integer> nonDistinctIntegersTopK = Arrays.asList(9, 9, 7, 12);
+
+
+    @Test
+    public void givenArrayDistinctIntegers_whenBruteForceFindTopK_thenReturnKLargest() {
+        assertThat(bruteForceFinder.findTopK(distinctIntegers, k)).containsOnlyElementsOf(distinctIntegersTopK);
+    }
+
+    @Test
+    public void givenArrayDistinctIntegers_whenMaxHeapFindTopK_thenReturnKLargest() {
+        assertThat(maxHeapFinder.findTopK(distinctIntegers, k)).containsOnlyElementsOf(distinctIntegersTopK);
+    }
+
+    @Test
+    public void givenArrayDistinctIntegers_whenTreeSetFindTopK_thenReturnKLargest() {
+        assertThat(treeSetFinder.findTopK(distinctIntegers, k)).containsOnlyElementsOf(distinctIntegersTopK);
+    }
+
+    @Test
+    public void givenArrayNonDistinctIntegers_whenBruteForceFindTopK_thenReturnKLargest() {
+        assertThat(bruteForceFinder.findTopK(nonDistinctIntegers, k)).containsOnlyElementsOf(nonDistinctIntegersTopK);
+    }
+
+    @Test
+    public void givenArrayNonDistinctIntegers_whenMaxHeapFindTopK_thenReturnKLargest() {
+        assertThat(maxHeapFinder.findTopK(nonDistinctIntegers, k)).containsOnlyElementsOf(nonDistinctIntegersTopK);
+    }
+}

apache-shiro/README.md

@@ -6,4 +6,4 @@ This module contains articles about Apache Shiro
 
 - [Introduction to Apache Shiro](https://www.baeldung.com/apache-shiro)
 - [Permissions-Based Access Control with Apache Shiro](https://www.baeldung.com/apache-shiro-access-control)
-
+- [Spring Security vs Apache Shiro](https://www.baeldung.com/spring-security-vs-apache-shiro)

core-groovy/README.md

@@ -13,4 +13,5 @@ This module contains articles about core Groovy concepts
 - [Converting a String to a Date in Groovy](https://www.baeldung.com/groovy-string-to-date)
 - [Guide to I/O in Groovy](https://www.baeldung.com/groovy-io)
 - [Convert String to Integer in Groovy](https://www.baeldung.com/groovy-convert-string-to-integer)
+- [Groovy Variable Scope](https://www.baeldung.com/groovy/variable-scope)
 - [[More -->]](/core-groovy-2)

core-java-modules/core-java-11/README.md

@@ -8,7 +8,7 @@ This module contains articles about Java 11 core features
 - [Java 11 Local Variable Syntax for Lambda Parameters](https://www.baeldung.com/java-var-lambda-params)
 - [Java 11 String API Additions](https://www.baeldung.com/java-11-string-api)
 - [Java 11 Nest Based Access Control](https://www.baeldung.com/java-nest-based-access-control)
-- [Exploring the New HTTP Client in Java 9 and 11](https://www.baeldung.com/java-9-http-client)
+- [Exploring the New HTTP Client in Java](https://www.baeldung.com/java-9-http-client)
 - [An Introduction to Epsilon GC: A No-Op Experimental Garbage Collector](https://www.baeldung.com/jvm-epsilon-gc-garbage-collector)
 - [Guide to jlink](https://www.baeldung.com/jlink)
 - [Negate a Predicate Method Reference with Java 11](https://www.baeldung.com/java-negate-predicate-method-reference)

core-java-modules/core-java-9-jigsaw/src/simple-modules/main.app/com/baeldung/modules/main/MainApp.java

@@ -1,12 +1,15 @@
 package com.baeldung.modules.main;
 
+import com.baeldung.modules.hello.HelloInterface;
 import com.baeldung.modules.hello.HelloModules;
+import java.util.ServiceLoader;
 
 public class MainApp {
     public static void main(String[] args) {
         HelloModules.doSomething();
-
-        HelloModules module = new HelloModules();
-        module.sayHello();
+        
+        Iterable<HelloInterface> services = ServiceLoader.load(HelloInterface.class);
+        HelloInterface service = services.iterator().next();
+        service.sayHello();
     }
 }

core-java-modules/core-java-9-new-features/README.md

@@ -13,3 +13,4 @@ This module contains articles about core Java features that have been introduced
 - [Java 9 Platform Logging API](https://www.baeldung.com/java-9-logging-api)
 - [Java 9 Reactive Streams](https://www.baeldung.com/java-9-reactive-streams)
 - [Multi-Release JAR Files with Maven](https://www.baeldung.com/maven-multi-release-jars)
+- [The Difference between RxJava API and the Java 9 Flow API](https://www.baeldung.com/rxjava-vs-java-flow-api)

core-java-modules/core-java-9/README.md

@@ -9,3 +9,4 @@ This module contains articles about Java 9 core features
 - [Iterate Through a Range of Dates in Java](https://www.baeldung.com/java-iterate-date-range)
 - [Initialize a HashMap in Java](https://www.baeldung.com/java-initialize-hashmap)
 - [Immutable ArrayList in Java](https://www.baeldung.com/java-immutable-list)
+- [Easy Ways to Write a Java InputStream to an OutputStream](https://www.baeldung.com/java-inputstream-to-outputstream)

core-java-modules/core-java-arrays-guides/README.md

@@ -5,4 +5,4 @@ This module contains complete guides about arrays in Java
 ### Relevant Articles: 
 - [Arrays in Java: A Reference Guide](https://www.baeldung.com/java-arrays-guide)
 - [Guide to the java.util.Arrays Class](https://www.baeldung.com/java-util-arrays)
-- [What is [Ljava.lang.Object;?]](https://www.baeldung.com/java-tostring-array)
+- [What is \[Ljava.lang.Object;?](https://www.baeldung.com/java-tostring-array)

core-java-modules/core-java-collections-3/README.md

@@ -3,6 +3,7 @@
 ## Core Java Collections Cookbooks and Examples
 
 ### Relevant Articles: 
+
 - [Time Comparison of Arrays.sort(Object[]) and Arrays.sort(int[])](https://www.baeldung.com/arrays-sortobject-vs-sortint)
 - [Java ArrayList vs Vector](https://www.baeldung.com/java-arraylist-vs-vector)
 - [Differences Between HashMap and Hashtable](https://www.baeldung.com/hashmap-hashtable-differences)
@@ -10,3 +11,4 @@
 - [Performance of contains() in a HashSet vs ArrayList](https://www.baeldung.com/java-hashset-arraylist-contains-performance)
 - [Fail-Safe Iterator vs Fail-Fast Iterator](https://www.baeldung.com/java-fail-safe-vs-fail-fast-iterator)
 - [Quick Guide to the Java Stack](https://www.baeldung.com/java-stack)
+- [Convert an Array of Primitives to a List](https://www.baeldung.com/java-primitive-array-to-list)

core-java-modules/core-java-concurrency-advanced-3/README.md

@@ -15,4 +15,5 @@ This module contains articles about advanced topics about multithreading with co
 - [The ABA Problem in Concurrency](https://www.baeldung.com/cs/aba-concurrency)
 - [Introduction to Lock-Free Data Structures](https://www.baeldung.com/lock-free-programming)
 - [Introduction to Exchanger in Java](https://www.baeldung.com/java-exchanger)
+- [Why Not To Start A Thread In The Constructor?](https://www.baeldung.com/java-thread-constructor)
 - [[<-- previous]](/core-java-modules/core-java-concurrency-advanced-2)

core-java-modules/core-java-concurrency-basic-2/README.md

@@ -3,10 +3,12 @@
 This module contains articles about basic Java concurrency
 
 ### Relevant Articles: 
+
 - [How to Delay Code Execution in Java](https://www.baeldung.com/java-delay-code-execution)
 - [wait and notify() Methods in Java](https://www.baeldung.com/java-wait-notify)
 - [Difference Between Wait and Sleep in Java](https://www.baeldung.com/java-wait-and-sleep)
 - [Guide to the Synchronized Keyword in Java](https://www.baeldung.com/java-synchronized)
 - [Life Cycle of a Thread in Java](https://www.baeldung.com/java-thread-lifecycle)
 - [Guide to AtomicMarkableReference](https://www.baeldung.com/java-atomicmarkablereference)
+- [Why are Local Variables Thread-Safe in Java](https://www.baeldung.com/java-local-variables-thread-safe)
 - [[<-- Prev]](/core-java-modules/core-java-concurrency-basic)

core-java-modules/core-java-date-operations-2/README.md

@@ -2,6 +2,7 @@
 This module contains articles about date operations in Java.
 
 ### Relevant Articles:
+
 - [Get the Current Date Prior to Java 8](https://www.baeldung.com/java-get-the-current-date-legacy)
 - [Skipping Weekends While Adding Days to LocalDate in Java 8](https://www.baeldung.com/java-localdate-add-days-skip-weekends)
 - [Checking If Two Java Dates Are on the Same Day](https://www.baeldung.com/java-check-two-dates-on-same-day)
@@ -9,4 +10,5 @@ This module contains articles about date operations in Java.
 - [How to Set the JVM Time Zone](https://www.baeldung.com/java-jvm-time-zone)
 - [How to determine day of week by passing specific date in Java?](https://www.baeldung.com/java-get-day-of-week)
 - [Finding Leap Years in Java](https://www.baeldung.com/java-leap-year)
+- [Getting the Week Number From Any Date](https://www.baeldung.com/java-get-week-number)
 - [[<-- Prev]](/core-java-modules/core-java-date-operations-1)

core-java-modules/core-java-exceptions-2/README.md

@@ -12,3 +12,5 @@ This module contains articles about core java exceptions
 - [Java – Try with Resources](https://www.baeldung.com/java-try-with-resources)
 - [Java Global Exception Handler](https://www.baeldung.com/java-global-exception-handler)
 - [How to Find an Exception’s Root Cause in Java](https://www.baeldung.com/java-exception-root-cause)
+- [Java IOException “Too many open files”](https://www.baeldung.com/java-too-many-open-files)
+- [When Does Java Throw the ExceptionInInitializerError?](https://www.baeldung.com/java-exceptionininitializererror)

core-java-modules/core-java-io-2/README.md

@@ -13,4 +13,4 @@ This module contains articles about core Java input and output (IO)
 - [How to Copy a File with Java](https://www.baeldung.com/java-copy-file)
 - [Create a Directory in Java](https://www.baeldung.com/java-create-directory) 
 - [Java IO vs NIO](https://www.baeldung.com/java-io-vs-nio)
-- [[<-- Prev]](/core-java-modules/core-java-io)
+- [[<-- Prev]](/core-java-modules/core-java-io)[[More -->]](/core-java-modules/core-java-io-3)

core-java-modules/core-java-io-3/README.md

@@ -0,0 +1,9 @@
+## Core Java IO
+
+This module contains articles about core Java input and output (IO)
+
+### Relevant Articles: 
+
+- [Java – Create a File](https://www.baeldung.com/java-how-to-create-a-file)
+- [Check If a Directory Is Empty in Java](https://www.baeldung.com/java-check-empty-directory)
+- [[<-- Prev]](/core-java-modules/core-java-io-2)

core-java-modules/core-java-io-3/pom.xml

@@ -0,0 +1,86 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project
+    xmlns="http://maven.apache.org/POM/4.0.0"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <artifactId>core-java-io-3</artifactId>
+    <version>0.1.0-SNAPSHOT</version>
+    <name>core-java-io-3</name>
+    <packaging>jar</packaging>
+    <parent>
+        <groupId>com.baeldung.core-java-modules</groupId>
+        <artifactId>core-java-modules</artifactId>
+        <version>0.0.1-SNAPSHOT</version>
+        <relativePath>../</relativePath>
+    </parent>
+
+    <dependencies>
+        <!-- utils -->
+        <dependency>
+            <groupId>com.google.guava</groupId>
+            <artifactId>guava</artifactId>
+            <version>${guava.version}</version>
+        </dependency>
+        <!-- utils -->
+        <dependency>
+            <groupId>commons-io</groupId>
+            <artifactId>commons-io</artifactId>
+            <version>${commons-io.version}</version>
+        </dependency>
+        <!-- logging -->
+        <dependency>
+            <groupId>log4j</groupId>
+            <artifactId>log4j</artifactId>
+            <version>${log4j.version}</version>
+        </dependency>
+        <dependency> <!-- needed to bridge to slf4j for projects that use the log4j APIs directly -->
+            <groupId>org.slf4j</groupId>
+            <artifactId>log4j-over-slf4j</artifactId>
+            <version>${org.slf4j.version}</version>
+        </dependency>
+        <!-- test scoped -->
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <version>${assertj.version}</version>
+            <scope>test</scope>
+        </dependency>
+        <!-- https://mvnrepository.com/artifact/com.github.tomakehurst/wiremock -->
+        <dependency>
+            <groupId>com.github.tomakehurst</groupId>
+            <artifactId>wiremock</artifactId>
+            <version>${wiremock.version}</version>
+            <scope>test</scope>
+        </dependency>
+
+    </dependencies>
+
+    <build>
+        <finalName>core-java-io-3</finalName>
+        <resources>
+            <resource>
+                <directory>src/main/resources</directory>
+                <filtering>true</filtering>
+            </resource>
+        </resources>
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-javadoc-plugin</artifactId>
+                <version>${maven-javadoc-plugin.version}</version>
+                <configuration>
+                    <source>${maven.compiler.source}</source>
+                    <target>${maven.compiler.target}</target>
+                </configuration>
+            </plugin>
+        </plugins>
+    </build>
+
+    <properties>
+        <assertj.version>3.6.1</assertj.version>
+        <maven-javadoc-plugin.version>3.0.0-M1</maven-javadoc-plugin.version>
+        <wiremock.version>2.26.3</wiremock.version>
+    </properties>
+
+</project>

core-java-modules/core-java-io-3/src/test/java/com/baeldung/createfile/CreateFileUnitTest.java

@@ -0,0 +1,50 @@
+package com.baeldung.createfile;
+
+import org.apache.commons.io.FileUtils;
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import java.io.File;
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+public class CreateFileUnitTest {
+
+    private final String FILE_NAME = "src/test/resources/fileToCreate.txt";
+
+    @AfterEach
+    @BeforeEach
+    public void cleanUpFiles() {
+        File targetFile = new File(FILE_NAME);
+        targetFile.delete();
+    }
+
+    @Test
+    public void givenUsingNio_whenCreatingFile_thenCorrect() throws IOException {
+        Path newFilePath = Paths.get(FILE_NAME);
+        Files.createFile(newFilePath);
+    }
+
+    @Test
+    public void givenUsingFile_whenCreatingFile_thenCorrect() throws IOException {
+        File newFile = new File(FILE_NAME);
+        boolean success = newFile.createNewFile();
+        assertTrue(success);
+    }
+
+    @Test
+    public void givenUsingGuava_whenCreatingFile_thenCorrect() throws IOException {
+        com.google.common.io.Files.touch(new File(FILE_NAME));
+    }
+
+    @Test
+    public void givenUsingCommonsIo_whenCreatingFile_thenCorrect() throws IOException {
+        FileUtils.touch(new File(FILE_NAME));
+    }
+
+}

core-java-modules/core-java-io-3/src/test/java/com/baeldung/emptiness/DirectoryEmptinessUnitTest.java

@@ -0,0 +1,63 @@
+package com.baeldung.emptiness;
+
+import org.junit.Test;
+
+import java.io.File;
+import java.io.IOException;
+import java.nio.file.DirectoryStream;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+import java.util.stream.Stream;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class DirectoryEmptinessUnitTest {
+
+    @Test
+    public void givenPath_whenInvalid_thenReturnsFalse() throws IOException {
+        assertThat(isEmpty(Paths.get("invalid-addr"))).isFalse();
+    }
+
+    @Test
+    public void givenPath_whenNotDirectory_thenReturnsFalse() throws IOException {
+        Path aFile = Paths.get(getClass().getResource("/notDir.txt").getPath());
+        assertThat(isEmpty(aFile)).isFalse();
+    }
+
+    @Test
+    public void givenPath_whenNotEmptyDir_thenReturnsFalse() throws IOException {
+        Path currentDir = new File("").toPath().toAbsolutePath();
+        assertThat(isEmpty(currentDir)).isFalse();
+    }
+
+    @Test
+    public void givenPath_whenIsEmpty_thenReturnsTrue() throws Exception {
+        Path path = Files.createTempDirectory("baeldung-empty");
+        assertThat(isEmpty(path)).isTrue();
+    }
+
+    private static boolean isEmpty(Path path) throws IOException {
+        if (Files.isDirectory(path)) {
+            try (DirectoryStream<Path> directory = Files.newDirectoryStream(path)) {
+                return !directory.iterator().hasNext();
+            }
+        }
+
+        return false;
+    }
+
+    private static boolean isEmpty2(Path path) throws IOException {
+        if (Files.isDirectory(path)) {
+            try (Stream<Path> entries = Files.list(path)) {
+                return !entries.findFirst().isPresent();
+            }
+        }
+
+        return false;
+    }
+
+    private static boolean isEmptyInefficient(Path path) {
+        return path.toFile().listFiles().length == 0;
+    }
+}

core-java-modules/core-java-io-apis/README.md

@@ -7,7 +7,6 @@ This module contains articles about core Java input/output(IO) APIs.
 - [A Guide to the Java FileReader Class](https://www.baeldung.com/java-filereader)
 - [The Java File Class](https://www.baeldung.com/java-io-file)
 - [Java FileWriter](https://www.baeldung.com/java-filewriter)
-- [Differences Between the Java WatchService API and the Apache Commons IO Monitor Library](https://www.baeldung.com/java-watchservice-vs-apache-commons-io-monitor-library)
 - [Comparing getPath(), getAbsolutePath(), and getCanonicalPath() in Java](https://www.baeldung.com/java-path)
 - [Quick Use of FilenameFilter](https://www.baeldung.com/java-filename-filter)
 - [Guide to BufferedReader](https://www.baeldung.com/java-buffered-reader)

core-java-modules/core-java-jvm-2/README.md

@@ -8,4 +8,6 @@ This module contains articles about working with the Java Virtual Machine (JVM).
 - [Measuring Object Sizes in the JVM](https://www.baeldung.com/jvm-measuring-object-sizes)
 - [Adding Shutdown Hooks for JVM Applications](https://www.baeldung.com/jvm-shutdown-hooks)
 - [boolean and boolean[] Memory Layout in the JVM](https://www.baeldung.com/jvm-boolean-memory-layout)
-- More articles: [[<-- prev]](/core-java-modules/core-java-jvm)
+- [Where Is the Array Length Stored in JVM?](https://www.baeldung.com/java-jvm-array-length)
+- [Memory Address of Objects in Java](https://www.baeldung.com/java-object-memory-address)
+- More articles: [[<-- prev]](/core-java-modules/core-java-jvm)

core-java-modules/core-java-lang-3/README.md

@@ -2,4 +2,6 @@
 
 This module contains articles about core features in the Java language
 
+- [Class.isInstance vs Class.isAssignableFrom](https://www.baeldung.com/java-isinstance-isassignablefrom)
+- [Converting a Java String Into a Boolean](https://www.baeldung.com/java-string-to-boolean)
 - [[<-- Prev]](/core-java-modules/core-java-lang-2)

core-java-modules/core-java-lang-3/pom.xml

@@ -39,4 +39,4 @@
         <assertj.version>3.12.2</assertj.version>
     </properties>
       
-</project>
+</project>

core-java-modules/core-java-lang-3/src/main/java/com/baeldung/staticvariables/StaticVariableDemo.java

@@ -0,0 +1,23 @@
+package com.baeldung.staticvariables;
+
+public class StaticVariableDemo {
+    public static int i;
+    public static int j = 20;
+    public static int z;
+
+    static {
+        z = 30;
+        a = 40;
+    }
+
+    public static int a = 50;
+
+    public static final int b = 100;
+
+    public StaticVariableDemo() {
+    }
+
+    static class Nested {
+        public static String nestedClassStaticVariable = "test";
+    }
+}

core-java-modules/core-java-lang-3/src/test/java/com/baeldung/staticvariables/StaticVariableUnitTest.java

@@ -0,0 +1,113 @@
+package com.baeldung.staticvariables;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import java.lang.reflect.Field;
+
+import org.junit.jupiter.api.Test;
+
+public class StaticVariableUnitTest {
+
+    @Test
+    public void initializeStaticVariable_checkAssignedValues() {
+
+        try {
+            Class<?> staticVariableDemo = this.getClass()
+                .getClassLoader()
+                .loadClass("com.baeldung.staticvariables.StaticVariableDemo");
+
+            Field field1 = staticVariableDemo.getField("i");
+
+            assertThat(field1.getInt(staticVariableDemo)).isEqualTo(0);
+
+            Field field2 = staticVariableDemo.getField("j");
+
+            assertThat(field2.getInt(staticVariableDemo)).isEqualTo(20);
+
+        } catch (ClassNotFoundException | NoSuchFieldException | SecurityException e) {
+            e.printStackTrace();
+        } catch (IllegalArgumentException e) {
+            e.printStackTrace();
+        } catch (IllegalAccessException e) {
+            e.printStackTrace();
+        }
+
+    }
+
+    @Test
+    public void initializeStaticVariable_checkStaticBlock() {
+
+        try {
+            Class<?> staticVariableDemo = this.getClass()
+                .getClassLoader()
+                .loadClass("com.baeldung.staticvariables.StaticVariableDemo");
+
+            Field field1 = staticVariableDemo.getField("z");
+
+            assertThat(field1.getInt(staticVariableDemo)).isEqualTo(30);
+
+            Field field2 = staticVariableDemo.getField("a");
+
+            assertThat(field2.getInt(staticVariableDemo)).isEqualTo(50);
+
+        } catch (ClassNotFoundException | NoSuchFieldException | SecurityException e) {
+            e.printStackTrace();
+        } catch (IllegalArgumentException e) {
+            e.printStackTrace();
+        } catch (IllegalAccessException e) {
+            e.printStackTrace();
+        }
+
+    }
+
+    @Test
+    public void initializeStaticVariable_checkFinalValues() {
+
+        try {
+            Class<?> staticVariableDemo = this.getClass()
+                .getClassLoader()
+                .loadClass("com.baeldung.staticvariables.StaticVariableDemo");
+
+            Field field1 = staticVariableDemo.getField("b");
+
+            assertThat(field1.getInt(staticVariableDemo)).isEqualTo(100);
+
+        } catch (ClassNotFoundException | NoSuchFieldException | SecurityException e) {
+            e.printStackTrace();
+        } catch (IllegalArgumentException e) {
+            e.printStackTrace();
+        } catch (IllegalAccessException e) {
+            e.printStackTrace();
+        }
+
+    }
+
+    @Test
+    public void initializeStaticVariable_checkInnerClassValues() {
+
+        try {
+            Class<?> staticVariableDemo = this.getClass()
+                .getClassLoader()
+                .loadClass("com.baeldung.staticvariables.StaticVariableDemo");
+
+            Class<?>[] nestedClasses = staticVariableDemo.getClasses();
+
+            for (Class<?> nestedClass : nestedClasses) {
+                if (nestedClass.getName()
+                    .equals("Nested")) {
+
+                    Field field1 = nestedClass.getField("nestedClassStaticVariable");
+                    assertThat(field1.get(nestedClass)).isEqualTo("test");
+                }
+            }
+
+        } catch (ClassNotFoundException | NoSuchFieldException | SecurityException e) {
+            e.printStackTrace();
+        } catch (IllegalArgumentException e) {
+            e.printStackTrace();
+        } catch (IllegalAccessException e) {
+            e.printStackTrace();
+        }
+
+    }
+}

core-java-modules/core-java-lang-oop-methods/README.md

@@ -3,7 +3,9 @@
 This module contains articles about methods in Java
 
 ### Relevant Articles: 
+
 - [Methods in Java](https://www.baeldung.com/java-methods)
 - [Method Overloading and Overriding in Java](https://www.baeldung.com/java-method-overload-override)
 - [Java equals() and hashCode() Contracts](https://www.baeldung.com/java-equals-hashcode-contracts)
 - [Guide to hashCode() in Java](https://www.baeldung.com/java-hashcode)
+- [The Covariant Return Type in Java](https://www.baeldung.com/java-covariant-return-type)

core-java-modules/core-java-networking-2/README.md

@@ -12,4 +12,5 @@ This module contains articles about networking in Java
 - [Authentication with HttpUrlConnection](https://www.baeldung.com/java-http-url-connection)
 - [Download a File from an URL in Java](https://www.baeldung.com/java-download-file)
 - [Handling java.net.ConnectException](https://www.baeldung.com/java-net-connectexception)
+- [Getting MAC addresses in Java](https://www.baeldung.com/java-mac-address)
 - [[<-- Prev]](/core-java-modules/core-java-networking)

core-java-modules/core-java-reflection-2/README.md

@@ -0,0 +1,3 @@
+### Relevant Articles:
+
+- [Reading the Value of ‘private’ Fields from a Different Class in Java](https://www.baeldung.com/java-reflection-read-private-field-value)

core-java-modules/core-java-reflection/README.MD

@@ -8,5 +8,4 @@
 - [Changing Annotation Parameters At Runtime](http://www.baeldung.com/java-reflection-change-annotation-params)
 - [Dynamic Proxies in Java](http://www.baeldung.com/java-dynamic-proxies)
 - [What Causes java.lang.reflect.InvocationTargetException?](https://www.baeldung.com/java-lang-reflect-invocationtargetexception)
-- [How to Find all Getters Returning Null](http://www.baeldung.com/java-getters-returning-null)
 - [How to Get a Name of a Method Being Executed?](http://www.baeldung.com/java-name-of-executing-method)

core-java-modules/core-java-regex/README.md

@@ -3,6 +3,7 @@
 ## Core Java 8 Cookbooks and Examples
 
 ### Relevant Articles: 
+
 - [An Overview of Regular Expressions Performance in Java](https://www.baeldung.com/java-regex-performance)
 - [A Guide To Java Regular Expressions API](http://www.baeldung.com/regular-expressions-java)
 - [Guide to Escaping Characters in Java RegExps](http://www.baeldung.com/java-regexp-escape-char)
@@ -11,3 +12,4 @@
 - [How to Use Regular Expressions to Replace Tokens in Strings](https://www.baeldung.com/java-regex-token-replacement)
 - [Regular Expressions \s and \s+ in Java](https://www.baeldung.com/java-regex-s-splus)
 - [Validate Phone Numbers With Java Regex](https://www.baeldung.com/java-regex-validate-phone-numbers)
+- [How to Count the Number of Matches for a Regex?](https://www.baeldung.com/java-count-regex-matches)

core-java-modules/core-java-security-2/README.md

@@ -9,4 +9,5 @@ This module contains articles about core Java Security
 - [Hashing a Password in Java](https://www.baeldung.com/java-password-hashing)
 - [SHA-256 and SHA3-256 Hashing in Java](https://www.baeldung.com/sha-256-hashing-java)
 - [Checksums in Java](https://www.baeldung.com/java-checksums)
+- [How to Read PEM File to Get Public and Private Keys](https://www.baeldung.com/java-read-pem-file-keys)
 - More articles: [[<-- prev]](/core-java-modules/core-java-security)

core-java-modules/core-java-string-operations-3/README.md

@@ -0,0 +1,3 @@
+### Relevant Articles:
+
+- [Version Comparison in Java](https://www.baeldung.com/java-comparing-versions)

core-java-modules/pom.xml

@@ -72,6 +72,7 @@
 
         <module>core-java-io</module>
         <module>core-java-io-2</module>
+        <module>core-java-io-3</module>
         <module>core-java-io-apis</module>
         <module>core-java-io-conversions</module>
         <module>core-java-io-conversions-2</module>

core-kotlin-modules/core-kotlin-collections/README.md

@@ -3,6 +3,7 @@
 This module contains articles about core Kotlin collections.
 
 ### Relevant articles:
+
 - [Split a List Into Parts in Kotlin](https://www.baeldung.com/kotlin-split-list-into-parts)
 - [Finding an Element in a List Using Kotlin](https://www.baeldung.com/kotlin-finding-element-in-list)
 - [Overview of Kotlin Collections API](https://www.baeldung.com/kotlin-collections-api)
@@ -12,3 +13,4 @@ This module contains articles about core Kotlin collections.
 - [Difference between fold and reduce in Kotlin](https://www.baeldung.com/kotlin/fold-vs-reduce)
 - [Guide to Sorting in Kotlin](https://www.baeldung.com/kotlin-sort)
 - [Working With Lists in Kotlin](https://www.baeldung.com/kotlin/lists)
+- [Iterating Collections by Index in Kotlin](https://www.baeldung.com/kotlin/iterating-collections-by-index)

core-kotlin-modules/core-kotlin-collections/src/main/kotlin/com/baeldung/index/IndexedIteration.kt

@@ -0,0 +1,33 @@
+package com.baeldung.index
+
+fun main() {
+
+    // Index only
+    val colors = listOf("Red", "Green", "Blue")
+    for (i in colors.indices) {
+        println(colors[i])
+    }
+
+    val colorArray = arrayOf("Red", "Green", "Blue")
+    for (i in colorArray.indices) {
+        println(colorArray[i])
+    }
+
+    (0 until colors.size).forEach { println(colors[it]) }
+    for (i in 0 until colors.size) {
+        println(colors[i])
+    }
+
+    // Index and Value
+    colors.forEachIndexed { i, v -> println("The value for index $i is $v") }
+    for (indexedValue in colors.withIndex()) {
+        println("The value for index ${indexedValue.index} is ${indexedValue.value}")
+    }
+
+    for ((i, v) in colors.withIndex()) {
+        println("The value for index $i is $v")
+    }
+
+    colors.filterIndexed { i, _ -> i % 2 == 0 }
+    colors.filterIndexed { _, v -> v == "RED" }
+}

core-kotlin-modules/core-kotlin-lang-oop-2/README.md

@@ -7,4 +7,5 @@ This module contains articles about Object-Oriented Programming in Kotlin
 - [Generics in Kotlin](https://www.baeldung.com/kotlin-generics)
 - [Delegated Properties in Kotlin](https://www.baeldung.com/kotlin-delegated-properties)
 - [Delegation Pattern in Kotlin](https://www.baeldung.com/kotlin-delegation-pattern)
+- [Anonymous Inner Classes in Kotlin](https://www.baeldung.com/kotlin/anonymous-inner-classes)
 - [[<-- Prev]](/core-kotlin-modules/core-kotlin-lang-oop)

core-kotlin-modules/core-kotlin-lang-oop-2/src/main/kotlin/com/baeldung/anonymous/Anonymous.kt

@@ -0,0 +1,41 @@
+package com.baeldung.anonymous
+
+import java.io.Serializable
+import java.nio.channels.Channel
+
+fun main() {
+    val channel = object : Channel {
+        override fun isOpen() = false
+
+        override fun close() {
+        }
+    }
+
+    val maxEntries = 10
+    val lruCache = object : LinkedHashMap<String, Int>(10, 0.75f) {
+
+        override fun removeEldestEntry(eldest: MutableMap.MutableEntry<String, Int>?): Boolean {
+            return size > maxEntries
+        }
+    }
+
+    val map = object : LinkedHashMap<String, Int>() {
+        // omitted
+    }
+
+    val serializableChannel = object : Channel, Serializable {
+        override fun isOpen(): Boolean {
+            TODO("Not yet implemented")
+        }
+
+        override fun close() {
+            TODO("Not yet implemented")
+        }
+    }
+
+    val obj = object {
+        val question = "answer"
+        val answer = 42
+    }
+    println("The ${obj.question} is ${obj.answer}")
+}

data-structures/README.md

@@ -11,3 +11,4 @@ This module contains articles about data structures in Java
 - [Introduction to Big Queue](https://www.baeldung.com/java-big-queue)
 - [Guide to AVL Trees in Java](https://www.baeldung.com/java-avl-trees)
 - [Graphs in Java](https://www.baeldung.com/java-graphs)
+- [Implementing a Ring Buffer in Java](https://www.baeldung.com/java-ring-buffer)

ddd/src/main/java/com/baeldung/ddd/order/config/CustomMongoConfiguration.java

@@ -0,0 +1,46 @@
+package com.baeldung.ddd.order.config;
+
+import org.bson.Document;
+import org.joda.money.CurrencyUnit;
+import org.joda.money.Money;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.core.convert.converter.Converter;
+import org.springframework.data.convert.ReadingConverter;
+import org.springframework.data.mongodb.core.convert.MongoCustomConversions;
+
+import java.math.BigDecimal;
+import java.util.Collections;
+
+@Configuration
+public class CustomMongoConfiguration {
+
+    @Bean
+    public MongoCustomConversions customConversions() {
+        return new MongoCustomConversions(Collections.singletonList(DocumentToMoneyConverter.INSTANCE));
+    }
+
+    @ReadingConverter
+    enum DocumentToMoneyConverter implements Converter<Document, Money> {
+
+        INSTANCE;
+
+        @Override
+        public Money convert(Document source) {
+            Document money = source.get("money", Document.class);
+
+            return Money.of(getCurrency(money), getAmount(money));
+        }
+
+        private CurrencyUnit getCurrency(Document money) {
+            Document currency = money.get("currency", Document.class);
+            String currencyCode = currency.getString("code");
+            return CurrencyUnit.of(currencyCode);
+        }
+
+        private BigDecimal getAmount(Document money) {
+            String amount = money.getString("amount");
+            return BigDecimal.valueOf(Double.parseDouble(amount));
+        }
+    }
+}

ddd/src/test/java/com/baeldung/ddd/order/jpa/PersistOrderLiveTest.java

@@ -1,19 +1,24 @@
 package com.baeldung.ddd.order.jpa;
 
-import static org.assertj.core.api.Assertions.assertThat;
-
-import java.math.BigDecimal;
-import java.util.Arrays;
-
 import org.junit.jupiter.api.DisplayName;
 import org.junit.jupiter.api.Test;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.boot.test.context.SpringBootTest;
 import org.springframework.test.context.junit.jupiter.SpringJUnitConfig;
 
+import java.math.BigDecimal;
+import java.util.Arrays;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/*
+ To run this test we need to run the databases first.
+ A dedicated docker-compose.yml file is located under the resources directory.
+ We can run it by simple executing `docker-compose up`.
+ */
 @SpringJUnitConfig
 @SpringBootTest
-public class PersistOrderIntegrationTest {
+public class PersistOrderLiveTest {
     @Autowired
     private JpaOrderRepository repository;
 

ddd/src/test/java/com/baeldung/ddd/order/mongo/OrderMongoLiveTest.java

@@ -17,9 +17,14 @@ import com.baeldung.ddd.order.Order;
 import com.baeldung.ddd.order.OrderLine;
 import com.baeldung.ddd.order.Product;
 
+/*
+ To run this test we need to run the databases first.
+ A dedicated docker-compose.yml file is located under the resources directory.
+ We can run it by simple executing `docker-compose up`.
+ */
 @SpringJUnitConfig
 @SpringBootTest
-public class OrderMongoIntegrationTest {
+public class OrderMongoLiveTest {
     @Autowired
     private OrderMongoRepository repo;
 

ddd/src/test/java/com/baeldung/dddhexagonalspring/infrastracture/repository/CassandraDbOrderRepositoryLiveTest.java

@@ -18,10 +18,15 @@ import com.baeldung.dddhexagonalspring.domain.Product;
 import com.baeldung.dddhexagonalspring.domain.repository.OrderRepository;
 import com.baeldung.dddhexagonalspring.infrastracture.repository.cassandra.SpringDataCassandraOrderRepository;
 
+/*
+ To run this test we need to run the databases first.
+ A dedicated docker-compose.yml file is located under the resources directory.
+ We can run it by simple executing `docker-compose up`.
+ */
 @SpringJUnitConfig
 @SpringBootTest
 @TestPropertySource("classpath:ddd-layers-test.properties")
-class CassandraDbOrderRepositoryIntegrationTest {
+class CassandraDbOrderRepositoryLiveTest {
 
     @Autowired
     private SpringDataCassandraOrderRepository cassandraOrderRepository;

ddd/src/test/java/com/baeldung/dddhexagonalspring/infrastracture/repository/MongoDbOrderRepositoryLiveTest.java

@@ -18,10 +18,15 @@ import com.baeldung.dddhexagonalspring.domain.Product;
 import com.baeldung.dddhexagonalspring.domain.repository.OrderRepository;
 import com.baeldung.dddhexagonalspring.infrastracture.repository.mongo.SpringDataMongoOrderRepository;
 
+/*
+ To run this test we need to run the databases first.
+ A dedicated docker-compose.yml file is located under the resources directory.
+ We can run it by simple executing `docker-compose up`.
+ */
 @SpringJUnitConfig
 @SpringBootTest
 @TestPropertySource("classpath:ddd-layers-test.properties")
-class MongoDbOrderRepositoryIntegrationTest {
+class MongoDbOrderRepositoryLiveTest {
 
     @Autowired
     private SpringDataMongoOrderRepository mongoOrderRepository;

docker/docker-spring-boot/mvnw

@@ -0,0 +1,310 @@
+#!/bin/sh
+# ----------------------------------------------------------------------------
+# 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
+#
+#    https://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.
+# ----------------------------------------------------------------------------
+
+# ----------------------------------------------------------------------------
+# Maven Start Up Batch script
+#
+# Required ENV vars:
+# ------------------
+#   JAVA_HOME - location of a JDK home dir
+#
+# Optional ENV vars
+# -----------------
+#   M2_HOME - location of maven2's installed home dir
+#   MAVEN_OPTS - parameters passed to the Java VM when running Maven
+#     e.g. to debug Maven itself, use
+#       set MAVEN_OPTS=-Xdebug -Xrunjdwp:transport=dt_socket,server=y,suspend=y,address=8000
+#   MAVEN_SKIP_RC - flag to disable loading of mavenrc files
+# ----------------------------------------------------------------------------
+
+if [ -z "$MAVEN_SKIP_RC" ] ; then
+
+  if [ -f /etc/mavenrc ] ; then
+    . /etc/mavenrc
+  fi
+
+  if [ -f "$HOME/.mavenrc" ] ; then
+    . "$HOME/.mavenrc"
+  fi
+
+fi
+
+# OS specific support.  $var _must_ be set to either true or false.
+cygwin=false;
+darwin=false;
+mingw=false
+case "`uname`" in
+  CYGWIN*) cygwin=true ;;
+  MINGW*) mingw=true;;
+  Darwin*) darwin=true
+    # Use /usr/libexec/java_home if available, otherwise fall back to /Library/Java/Home
+    # See https://developer.apple.com/library/mac/qa/qa1170/_index.html
+    if [ -z "$JAVA_HOME" ]; then
+      if [ -x "/usr/libexec/java_home" ]; then
+        export JAVA_HOME="`/usr/libexec/java_home`"
+      else
+        export JAVA_HOME="/Library/Java/Home"
+      fi
+    fi
+    ;;
+esac
+
+if [ -z "$JAVA_HOME" ] ; then
+  if [ -r /etc/gentoo-release ] ; then
+    JAVA_HOME=`java-config --jre-home`
+  fi
+fi
+
+if [ -z "$M2_HOME" ] ; then
+  ## resolve links - $0 may be a link to maven's home
+  PRG="$0"
+
+  # need this for relative symlinks
+  while [ -h "$PRG" ] ; do
+    ls=`ls -ld "$PRG"`
+    link=`expr "$ls" : '.*-> \(.*\)$'`
+    if expr "$link" : '/.*' > /dev/null; then
+      PRG="$link"
+    else
+      PRG="`dirname "$PRG"`/$link"
+    fi
+  done
+
+  saveddir=`pwd`
+
+  M2_HOME=`dirname "$PRG"`/..
+
+  # make it fully qualified
+  M2_HOME=`cd "$M2_HOME" && pwd`
+
+  cd "$saveddir"
+  # echo Using m2 at $M2_HOME
+fi
+
+# For Cygwin, ensure paths are in UNIX format before anything is touched
+if $cygwin ; then
+  [ -n "$M2_HOME" ] &&
+    M2_HOME=`cygpath --unix "$M2_HOME"`
+  [ -n "$JAVA_HOME" ] &&
+    JAVA_HOME=`cygpath --unix "$JAVA_HOME"`
+  [ -n "$CLASSPATH" ] &&
+    CLASSPATH=`cygpath --path --unix "$CLASSPATH"`
+fi
+
+# For Mingw, ensure paths are in UNIX format before anything is touched
+if $mingw ; then
+  [ -n "$M2_HOME" ] &&
+    M2_HOME="`(cd "$M2_HOME"; pwd)`"
+  [ -n "$JAVA_HOME" ] &&
+    JAVA_HOME="`(cd "$JAVA_HOME"; pwd)`"
+fi
+
+if [ -z "$JAVA_HOME" ]; then
+  javaExecutable="`which javac`"
+  if [ -n "$javaExecutable" ] && ! [ "`expr \"$javaExecutable\" : '\([^ ]*\)'`" = "no" ]; then
+    # readlink(1) is not available as standard on Solaris 10.
+    readLink=`which readlink`
+    if [ ! `expr "$readLink" : '\([^ ]*\)'` = "no" ]; then
+      if $darwin ; then
+        javaHome="`dirname \"$javaExecutable\"`"
+        javaExecutable="`cd \"$javaHome\" && pwd -P`/javac"
+      else
+        javaExecutable="`readlink -f \"$javaExecutable\"`"
+      fi
+      javaHome="`dirname \"$javaExecutable\"`"
+      javaHome=`expr "$javaHome" : '\(.*\)/bin'`
+      JAVA_HOME="$javaHome"
+      export JAVA_HOME
+    fi
+  fi
+fi
+
+if [ -z "$JAVACMD" ] ; then
+  if [ -n "$JAVA_HOME"  ] ; then
+    if [ -x "$JAVA_HOME/jre/sh/java" ] ; then
+      # IBM's JDK on AIX uses strange locations for the executables
+      JAVACMD="$JAVA_HOME/jre/sh/java"
+    else
+      JAVACMD="$JAVA_HOME/bin/java"
+    fi
+  else
+    JAVACMD="`which java`"
+  fi
+fi
+
+if [ ! -x "$JAVACMD" ] ; then
+  echo "Error: JAVA_HOME is not defined correctly." >&2
+  echo "  We cannot execute $JAVACMD" >&2
+  exit 1
+fi
+
+if [ -z "$JAVA_HOME" ] ; then
+  echo "Warning: JAVA_HOME environment variable is not set."
+fi
+
+CLASSWORLDS_LAUNCHER=org.codehaus.plexus.classworlds.launcher.Launcher
+
+# traverses directory structure from process work directory to filesystem root
+# first directory with .mvn subdirectory is considered project base directory
+find_maven_basedir() {
+
+  if [ -z "$1" ]
+  then
+    echo "Path not specified to find_maven_basedir"
+    return 1
+  fi
+
+  basedir="$1"
+  wdir="$1"
+  while [ "$wdir" != '/' ] ; do
+    if [ -d "$wdir"/.mvn ] ; then
+      basedir=$wdir
+      break
+    fi
+    # workaround for JBEAP-8937 (on Solaris 10/Sparc)
+    if [ -d "${wdir}" ]; then
+      wdir=`cd "$wdir/.."; pwd`
+    fi
+    # end of workaround
+  done
+  echo "${basedir}"
+}
+
+# concatenates all lines of a file
+concat_lines() {
+  if [ -f "$1" ]; then
+    echo "$(tr -s '\n' ' ' < "$1")"
+  fi
+}
+
+BASE_DIR=`find_maven_basedir "$(pwd)"`
+if [ -z "$BASE_DIR" ]; then
+  exit 1;
+fi
+
+##########################################################################################
+# Extension to allow automatically downloading the maven-wrapper.jar from Maven-central
+# This allows using the maven wrapper in projects that prohibit checking in binary data.
+##########################################################################################
+if [ -r "$BASE_DIR/.mvn/wrapper/maven-wrapper.jar" ]; then
+    if [ "$MVNW_VERBOSE" = true ]; then
+      echo "Found .mvn/wrapper/maven-wrapper.jar"
+    fi
+else
+    if [ "$MVNW_VERBOSE" = true ]; then
+      echo "Couldn't find .mvn/wrapper/maven-wrapper.jar, downloading it ..."
+    fi
+    if [ -n "$MVNW_REPOURL" ]; then
+      jarUrl="$MVNW_REPOURL/io/takari/maven-wrapper/0.5.6/maven-wrapper-0.5.6.jar"
+    else
+      jarUrl="https://repo.maven.apache.org/maven2/io/takari/maven-wrapper/0.5.6/maven-wrapper-0.5.6.jar"
+    fi
+    while IFS="=" read key value; do
+      case "$key" in (wrapperUrl) jarUrl="$value"; break ;;
+      esac
+    done < "$BASE_DIR/.mvn/wrapper/maven-wrapper.properties"
+    if [ "$MVNW_VERBOSE" = true ]; then
+      echo "Downloading from: $jarUrl"
+    fi
+    wrapperJarPath="$BASE_DIR/.mvn/wrapper/maven-wrapper.jar"
+    if $cygwin; then
+      wrapperJarPath=`cygpath --path --windows "$wrapperJarPath"`
+    fi
+
+    if command -v wget > /dev/null; then
+        if [ "$MVNW_VERBOSE" = true ]; then
+          echo "Found wget ... using wget"
+        fi
+        if [ -z "$MVNW_USERNAME" ] || [ -z "$MVNW_PASSWORD" ]; then
+            wget "$jarUrl" -O "$wrapperJarPath"
+        else
+            wget --http-user=$MVNW_USERNAME --http-password=$MVNW_PASSWORD "$jarUrl" -O "$wrapperJarPath"
+        fi
+    elif command -v curl > /dev/null; then
+        if [ "$MVNW_VERBOSE" = true ]; then
+          echo "Found curl ... using curl"
+        fi
+        if [ -z "$MVNW_USERNAME" ] || [ -z "$MVNW_PASSWORD" ]; then
+            curl -o "$wrapperJarPath" "$jarUrl" -f
+        else
+            curl --user $MVNW_USERNAME:$MVNW_PASSWORD -o "$wrapperJarPath" "$jarUrl" -f
+        fi
+
+    else
+        if [ "$MVNW_VERBOSE" = true ]; then
+          echo "Falling back to using Java to download"
+        fi
+        javaClass="$BASE_DIR/.mvn/wrapper/MavenWrapperDownloader.java"
+        # For Cygwin, switch paths to Windows format before running javac
+        if $cygwin; then
+          javaClass=`cygpath --path --windows "$javaClass"`
+        fi
+        if [ -e "$javaClass" ]; then
+            if [ ! -e "$BASE_DIR/.mvn/wrapper/MavenWrapperDownloader.class" ]; then
+                if [ "$MVNW_VERBOSE" = true ]; then
+                  echo " - Compiling MavenWrapperDownloader.java ..."
+                fi
+                # Compiling the Java class
+                ("$JAVA_HOME/bin/javac" "$javaClass")
+            fi
+            if [ -e "$BASE_DIR/.mvn/wrapper/MavenWrapperDownloader.class" ]; then
+                # Running the downloader
+                if [ "$MVNW_VERBOSE" = true ]; then
+                  echo " - Running MavenWrapperDownloader.java ..."
+                fi
+                ("$JAVA_HOME/bin/java" -cp .mvn/wrapper MavenWrapperDownloader "$MAVEN_PROJECTBASEDIR")
+            fi
+        fi
+    fi
+fi
+##########################################################################################
+# End of extension
+##########################################################################################
+
+export MAVEN_PROJECTBASEDIR=${MAVEN_BASEDIR:-"$BASE_DIR"}
+if [ "$MVNW_VERBOSE" = true ]; then
+  echo $MAVEN_PROJECTBASEDIR
+fi
+MAVEN_OPTS="$(concat_lines "$MAVEN_PROJECTBASEDIR/.mvn/jvm.config") $MAVEN_OPTS"
+
+# For Cygwin, switch paths to Windows format before running java
+if $cygwin; then
+  [ -n "$M2_HOME" ] &&
+    M2_HOME=`cygpath --path --windows "$M2_HOME"`
+  [ -n "$JAVA_HOME" ] &&
+    JAVA_HOME=`cygpath --path --windows "$JAVA_HOME"`
+  [ -n "$CLASSPATH" ] &&
+    CLASSPATH=`cygpath --path --windows "$CLASSPATH"`
+  [ -n "$MAVEN_PROJECTBASEDIR" ] &&
+    MAVEN_PROJECTBASEDIR=`cygpath --path --windows "$MAVEN_PROJECTBASEDIR"`
+fi
+
+# Provide a "standardized" way to retrieve the CLI args that will
+# work with both Windows and non-Windows executions.
+MAVEN_CMD_LINE_ARGS="$MAVEN_CONFIG $@"
+export MAVEN_CMD_LINE_ARGS
+
+WRAPPER_LAUNCHER=org.apache.maven.wrapper.MavenWrapperMain
+
+exec "$JAVACMD" \
+  $MAVEN_OPTS \
+  -classpath "$MAVEN_PROJECTBASEDIR/.mvn/wrapper/maven-wrapper.jar" \
+  "-Dmaven.home=${M2_HOME}" "-Dmaven.multiModuleProjectDirectory=${MAVEN_PROJECTBASEDIR}" \
+  ${WRAPPER_LAUNCHER} $MAVEN_CONFIG "$@"

docker/docker-spring-boot/mvnw.cmd

@@ -0,0 +1,182 @@
+@REM ----------------------------------------------------------------------------
+@REM Licensed to the Apache Software Foundation (ASF) under one
+@REM or more contributor license agreements.  See the NOTICE file
+@REM distributed with this work for additional information
+@REM regarding copyright ownership.  The ASF licenses this file
+@REM to you under the Apache License, Version 2.0 (the
+@REM "License"); you may not use this file except in compliance
+@REM with the License.  You may obtain a copy of the License at
+@REM
+@REM    https://www.apache.org/licenses/LICENSE-2.0
+@REM
+@REM Unless required by applicable law or agreed to in writing,
+@REM software distributed under the License is distributed on an
+@REM "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+@REM KIND, either express or implied.  See the License for the
+@REM specific language governing permissions and limitations
+@REM under the License.
+@REM ----------------------------------------------------------------------------
+
+@REM ----------------------------------------------------------------------------
+@REM Maven Start Up Batch script
+@REM
+@REM Required ENV vars:
+@REM JAVA_HOME - location of a JDK home dir
+@REM
+@REM Optional ENV vars
+@REM M2_HOME - location of maven2's installed home dir
+@REM MAVEN_BATCH_ECHO - set to 'on' to enable the echoing of the batch commands
+@REM MAVEN_BATCH_PAUSE - set to 'on' to wait for a keystroke before ending
+@REM MAVEN_OPTS - parameters passed to the Java VM when running Maven
+@REM     e.g. to debug Maven itself, use
+@REM set MAVEN_OPTS=-Xdebug -Xrunjdwp:transport=dt_socket,server=y,suspend=y,address=8000
+@REM MAVEN_SKIP_RC - flag to disable loading of mavenrc files
+@REM ----------------------------------------------------------------------------
+
+@REM Begin all REM lines with '@' in case MAVEN_BATCH_ECHO is 'on'
+@echo off
+@REM set title of command window
+title %0
+@REM enable echoing by setting MAVEN_BATCH_ECHO to 'on'
+@if "%MAVEN_BATCH_ECHO%" == "on"  echo %MAVEN_BATCH_ECHO%
+
+@REM set %HOME% to equivalent of $HOME
+if "%HOME%" == "" (set "HOME=%HOMEDRIVE%%HOMEPATH%")
+
+@REM Execute a user defined script before this one
+if not "%MAVEN_SKIP_RC%" == "" goto skipRcPre
+@REM check for pre script, once with legacy .bat ending and once with .cmd ending
+if exist "%HOME%\mavenrc_pre.bat" call "%HOME%\mavenrc_pre.bat"
+if exist "%HOME%\mavenrc_pre.cmd" call "%HOME%\mavenrc_pre.cmd"
+:skipRcPre
+
+@setlocal
+
+set ERROR_CODE=0
+
+@REM To isolate internal variables from possible post scripts, we use another setlocal
+@setlocal
+
+@REM ==== START VALIDATION ====
+if not "%JAVA_HOME%" == "" goto OkJHome
+
+echo.
+echo Error: JAVA_HOME not found in your environment. >&2
+echo Please set the JAVA_HOME variable in your environment to match the >&2
+echo location of your Java installation. >&2
+echo.
+goto error
+
+:OkJHome
+if exist "%JAVA_HOME%\bin\java.exe" goto init
+
+echo.
+echo Error: JAVA_HOME is set to an invalid directory. >&2
+echo JAVA_HOME = "%JAVA_HOME%" >&2
+echo Please set the JAVA_HOME variable in your environment to match the >&2
+echo location of your Java installation. >&2
+echo.
+goto error
+
+@REM ==== END VALIDATION ====
+
+:init
+
+@REM Find the project base dir, i.e. the directory that contains the folder ".mvn".
+@REM Fallback to current working directory if not found.
+
+set MAVEN_PROJECTBASEDIR=%MAVEN_BASEDIR%
+IF NOT "%MAVEN_PROJECTBASEDIR%"=="" goto endDetectBaseDir
+
+set EXEC_DIR=%CD%
+set WDIR=%EXEC_DIR%
+:findBaseDir
+IF EXIST "%WDIR%"\.mvn goto baseDirFound
+cd ..
+IF "%WDIR%"=="%CD%" goto baseDirNotFound
+set WDIR=%CD%
+goto findBaseDir
+
+:baseDirFound
+set MAVEN_PROJECTBASEDIR=%WDIR%
+cd "%EXEC_DIR%"
+goto endDetectBaseDir
+
+:baseDirNotFound
+set MAVEN_PROJECTBASEDIR=%EXEC_DIR%
+cd "%EXEC_DIR%"
+
+:endDetectBaseDir
+
+IF NOT EXIST "%MAVEN_PROJECTBASEDIR%\.mvn\jvm.config" goto endReadAdditionalConfig
+
+@setlocal EnableExtensions EnableDelayedExpansion
+for /F "usebackq delims=" %%a in ("%MAVEN_PROJECTBASEDIR%\.mvn\jvm.config") do set JVM_CONFIG_MAVEN_PROPS=!JVM_CONFIG_MAVEN_PROPS! %%a
+@endlocal & set JVM_CONFIG_MAVEN_PROPS=%JVM_CONFIG_MAVEN_PROPS%
+
+:endReadAdditionalConfig
+
+SET MAVEN_JAVA_EXE="%JAVA_HOME%\bin\java.exe"
+set WRAPPER_JAR="%MAVEN_PROJECTBASEDIR%\.mvn\wrapper\maven-wrapper.jar"
+set WRAPPER_LAUNCHER=org.apache.maven.wrapper.MavenWrapperMain
+
+set DOWNLOAD_URL="https://repo.maven.apache.org/maven2/io/takari/maven-wrapper/0.5.6/maven-wrapper-0.5.6.jar"
+
+FOR /F "tokens=1,2 delims==" %%A IN ("%MAVEN_PROJECTBASEDIR%\.mvn\wrapper\maven-wrapper.properties") DO (
+    IF "%%A"=="wrapperUrl" SET DOWNLOAD_URL=%%B
+)
+
+@REM Extension to allow automatically downloading the maven-wrapper.jar from Maven-central
+@REM This allows using the maven wrapper in projects that prohibit checking in binary data.
+if exist %WRAPPER_JAR% (
+    if "%MVNW_VERBOSE%" == "true" (
+        echo Found %WRAPPER_JAR%
+    )
+) else (
+    if not "%MVNW_REPOURL%" == "" (
+        SET DOWNLOAD_URL="%MVNW_REPOURL%/io/takari/maven-wrapper/0.5.6/maven-wrapper-0.5.6.jar"
+    )
+    if "%MVNW_VERBOSE%" == "true" (
+        echo Couldn't find %WRAPPER_JAR%, downloading it ...
+        echo Downloading from: %DOWNLOAD_URL%
+    )
+
+    powershell -Command "&{"^
+		"$webclient = new-object System.Net.WebClient;"^
+		"if (-not ([string]::IsNullOrEmpty('%MVNW_USERNAME%') -and [string]::IsNullOrEmpty('%MVNW_PASSWORD%'))) {"^
+		"$webclient.Credentials = new-object System.Net.NetworkCredential('%MVNW_USERNAME%', '%MVNW_PASSWORD%');"^
+		"}"^
+		"[Net.ServicePointManager]::SecurityProtocol = [Net.SecurityProtocolType]::Tls12; $webclient.DownloadFile('%DOWNLOAD_URL%', '%WRAPPER_JAR%')"^
+		"}"
+    if "%MVNW_VERBOSE%" == "true" (
+        echo Finished downloading %WRAPPER_JAR%
+    )
+)
+@REM End of extension
+
+@REM Provide a "standardized" way to retrieve the CLI args that will
+@REM work with both Windows and non-Windows executions.
+set MAVEN_CMD_LINE_ARGS=%*
+
+%MAVEN_JAVA_EXE% %JVM_CONFIG_MAVEN_PROPS% %MAVEN_OPTS% %MAVEN_DEBUG_OPTS% -classpath %WRAPPER_JAR% "-Dmaven.multiModuleProjectDirectory=%MAVEN_PROJECTBASEDIR%" %WRAPPER_LAUNCHER% %MAVEN_CONFIG% %*
+if ERRORLEVEL 1 goto error
+goto end
+
+:error
+set ERROR_CODE=1
+
+:end
+@endlocal & set ERROR_CODE=%ERROR_CODE%
+
+if not "%MAVEN_SKIP_RC%" == "" goto skipRcPost
+@REM check for post script, once with legacy .bat ending and once with .cmd ending
+if exist "%HOME%\mavenrc_post.bat" call "%HOME%\mavenrc_post.bat"
+if exist "%HOME%\mavenrc_post.cmd" call "%HOME%\mavenrc_post.cmd"
+:skipRcPost
+
+@REM pause the script if MAVEN_BATCH_PAUSE is set to 'on'
+if "%MAVEN_BATCH_PAUSE%" == "on" pause
+
+if "%MAVEN_TERMINATE_CMD%" == "on" exit %ERROR_CODE%
+
+exit /B %ERROR_CODE%

docker/docker-spring-boot/pom.xml

@@ -0,0 +1,54 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <parent>
+        <groupId>org.springframework.boot</groupId>
+        <artifactId>spring-boot-starter-parent</artifactId>
+        <version>2.3.1.RELEASE</version>
+        <relativePath/> <!-- lookup parent from repository -->
+    </parent>
+    <groupId>com.baeldung.docker</groupId>
+    <artifactId>spring-boot-docker</artifactId>
+    <version>0.0.1-SNAPSHOT</version>
+    <name>spring-boot-docker</name>
+    <description>Demo project showing Spring Boot and Docker</description>
+
+    <properties>
+        <java.version>8</java.version>
+    </properties>
+
+    <dependencies>
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-web</artifactId>
+        </dependency>
+
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-test</artifactId>
+            <scope>test</scope>
+            <exclusions>
+                <exclusion>
+                    <groupId>org.junit.vintage</groupId>
+                    <artifactId>junit-vintage-engine</artifactId>
+                </exclusion>
+            </exclusions>
+        </dependency>
+    </dependencies>
+
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.springframework.boot</groupId>
+                <artifactId>spring-boot-maven-plugin</artifactId>
+                <configuration>
+                    <layers>
+                        <enabled>true</enabled>
+                    </layers>
+                </configuration>
+            </plugin>
+        </plugins>
+    </build>
+
+</project>

docker/docker-spring-boot/src/main/docker/Dockerfile

@@ -0,0 +1,15 @@
+# To build, run the following command from the top level project directory:
+#
+# docker build -f src/main/docker/Dockerfile .
+
+FROM adoptopenjdk:11-jre-hotspot as builder
+ARG JAR_FILE=target/*.jar
+COPY ${JAR_FILE} application.jar
+RUN java -Djarmode=layertools -jar application.jar extract
+
+FROM adoptopenjdk:11-jre-hotspot
+COPY --from=builder dependencies/ ./
+COPY --from=builder snapshot-dependencies/ ./
+COPY --from=builder spring-boot-loader/ ./
+COPY --from=builder application/ ./
+ENTRYPOINT ["java", "org.springframework.boot.loader.JarLauncher"]

docker/docker-spring-boot/src/main/java/com/baeldung/docker/DemoApplication.java

@@ -0,0 +1,13 @@
+package com.baeldung.docker;
+
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+
+@SpringBootApplication
+public class DemoApplication {
+
+    public static void main(String[] args) {
+        SpringApplication.run(DemoApplication.class, args);
+    }
+
+}

docker/docker-spring-boot/src/main/java/com/baeldung/docker/HelloController.java

@@ -0,0 +1,16 @@
+package com.baeldung.docker;
+
+import org.springframework.http.ResponseEntity;
+import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.RestController;
+
+@RestController
+public class HelloController {
+
+    @GetMapping("/hello")
+    public ResponseEntity<String> hello()
+    {
+        return ResponseEntity.ok("hello2    ");
+    }
+
+}

docker/docker-spring-boot/src/main/resources/application.properties

@@ -0,0 +1 @@
+

gradle-5/README.md

@@ -1,3 +1,4 @@
 ### Relevant Articles:
 
 - [Run a Java main Method Using Gradle](https://www.baeldung.com/gradle-run-java-main)
+- [Finding Unused Gradle Dependencies](https://www.baeldung.com/gradle-finding-unused-dependencies)

guava-2/README.md

@@ -3,5 +3,5 @@
 This module contains articles a Google Guava
 
 ### Relevant Articles: 
-- [Introduction to Guava Throwables](https://www.baeldung.com/guava-throwables)
+
 - [Guava CharMatcher](https://www.baeldung.com/guava-string-charmatcher)

guava/README.md

@@ -3,6 +3,7 @@
 This module contains articles a Google Guava
 
 ### Relevant Articles: 
+
 - [Guava Functional Cookbook](https://www.baeldung.com/guava-functions-predicates)
 - [Guide to Guava’s PreConditions](https://www.baeldung.com/guava-preconditions)
 - [Introduction to Guava CacheLoader](https://www.baeldung.com/guava-cacheloader)
@@ -13,3 +14,4 @@ This module contains articles a Google Guava
 - [Bloom Filter in Java using Guava](https://www.baeldung.com/guava-bloom-filter)
 - [Quick Guide to the Guava RateLimiter](https://www.baeldung.com/guava-rate-limiter)
 - [Guava Cache](https://www.baeldung.com/guava-cache)
+- [Introduction to Guava Throwables](https://www.baeldung.com/guava-throwables)

image-processing/README.md

@@ -6,3 +6,5 @@ This module contains articles about image processing.
 - [Working with Images in Java](https://www.baeldung.com/java-images)
 - [Intro to OpenCV with Java](https://www.baeldung.com/java-opencv)
 - [Optical Character Recognition with Tesseract](https://www.baeldung.com/java-ocr-tesseract)
+- [How Can I Resize an Image Using Java?](https://www.baeldung.com/java-resize-image)
+- [Adding Text to an Image in Java](https://www.baeldung.com/java-add-text-to-image)

java-collections-conversions-2/src/main/java/com/baeldung/convertlisttomap/ListToMapConverter.java

@@ -0,0 +1,70 @@
+package com.baeldung.convertlisttomap;
+
+import java.util.List;
+import java.util.Map;
+import java.util.function.BiConsumer;
+import java.util.function.BinaryOperator;
+import java.util.function.Function;
+import java.util.function.Supplier;
+import java.util.stream.Collectors;
+
+/**
+ * Convert a string list to a map whose key is the string's length and value is the collection with same length.
+ * Give a list {"Baeldung", "is", "very", "cool"}.
+ * After conversion we'll get a map like:
+ * {8 : ["Baeldung"], 2 : ["is"], 4 : ["very", "cool"]}.
+ * 
+ * @author leasy.zhang
+ *
+ */
+public class ListToMapConverter {
+
+    public Map<Integer, List<String>> groupingByStringLength(List<String> source, 
+        Supplier<Map<Integer, List<String>>> mapSupplier, 
+        Supplier<List<String>> listSupplier) {
+        
+        return source.stream()
+            .collect(Collectors.groupingBy(String::length, mapSupplier, Collectors.toCollection(listSupplier)));
+    }
+    
+    public Map<Integer, List<String>> streamCollectByStringLength(List<String> source, 
+        Supplier<Map<Integer, List<String>>> mapSupplier, 
+        Supplier<List<String>> listSupplier) {
+        
+        BiConsumer<Map<Integer, List<String>>, String> accumulator = (response, element) -> {
+            Integer key = element.length();
+            List<String> values = response.getOrDefault(key, listSupplier.get());
+            values.add(element);
+            response.put(key, values);
+        };
+
+        BiConsumer<Map<Integer, List<String>>, Map<Integer, List<String>>> combiner = (res1, res2) -> {
+            res1.putAll(res2);
+        };
+
+        return source.stream()
+            .collect(mapSupplier, accumulator, combiner);
+    }
+    
+    public Map<Integer, List<String>> collectorToMapByStringLength(List<String> source, 
+        Supplier<Map<Integer, List<String>>> mapSupplier, 
+        Supplier<List<String>> listSupplier) {
+        
+        Function<String, Integer> keyMapper = String::length;
+
+        Function<String, List<String>> valueMapper = (element) -> {
+            List<String> collection = listSupplier.get();
+            collection.add(element);
+            return collection;
+        };
+
+        BinaryOperator<List<String>> mergeFunction = (existing, replacement) -> {
+            existing.addAll(replacement);
+            return existing;
+        };
+
+        return source.stream()
+            .collect(Collectors.toMap(keyMapper, valueMapper, mergeFunction, mapSupplier));
+    }
+
+}

java-collections-conversions-2/src/test/java/com/baeldung/convertlisttomap/ListToMapUnitTest.java

@@ -0,0 +1,46 @@
+package com.baeldung.convertlisttomap;
+
+import static org.junit.Assert.assertTrue;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+import org.junit.Before;
+import org.junit.Test;
+
+public class ListToMapUnitTest {
+
+    private ListToMapConverter converter;
+    private List<String> source;
+
+    @Before
+    public void setUp() {
+        converter = new ListToMapConverter();
+        source = Arrays.asList("List", "Map", "Set", "Tree");
+    }
+
+    @Test
+    public void givenAList_whenConvertWithJava8GroupBy_thenReturnMap() {
+        Map<Integer, List<String>> convertedMap = converter.groupingByStringLength(source, HashMap::new, ArrayList::new);
+        assertTrue(convertedMap.get(3)
+            .contains("Map"));
+    }
+
+    @Test
+    public void givenAList_whenConvertWithJava8Collect_thenReturnMap() {
+        Map<Integer, List<String>> convertedMap = converter.streamCollectByStringLength(source, HashMap::new, ArrayList::new);
+        assertTrue(convertedMap.get(3)
+            .contains("Map"));
+    }
+
+    @Test
+    public void givenAList_whenConvertWithCollectorToMap_thenReturnMap() {
+        Map<Integer, List<String>> convertedMap = converter.collectorToMapByStringLength(source, HashMap::new, ArrayList::new);
+        assertTrue(convertedMap.get(3)
+            .contains("Map"));
+    }
+
+}

java-numbers-3/README.md

@@ -11,4 +11,7 @@ This module contains articles about numbers in Java.
 - [Listing Numbers Within a Range in Java](https://www.baeldung.com/java-listing-numbers-within-a-range)
 - [Fibonacci Series in Java](https://www.baeldung.com/java-fibonacci)
 - [Guide to the Number Class in Java](https://www.baeldung.com/java-number-class)
+- [Print an Integer in Binary Format in Java](https://www.baeldung.com/java-print-integer-binary)
+- [Number Formatting in Java](https://www.baeldung.com/java-number-formatting)
+- [Division by Zero in Java: Exception, Infinity, or Not a Number](https://www.baeldung.com/java-division-by-zero)
 - More articles: [[<-- prev]](/java-numbers-2)

jmh/README.md

@@ -5,4 +5,4 @@ This module contains articles about the Java Microbenchmark Harness (JMH).
 ### Relevant articles:
 
 - [Microbenchmarking with Java](https://www.baeldung.com/java-microbenchmark-harness)
-
+- [A Guide to False Sharing and @Contended](https://www.baeldung.com/java-false-sharing-contended)

jmh/src/main/java/com/baeldung/falsesharing/FalseSharing.java

@@ -0,0 +1,22 @@
+package com.baeldung.falsesharing;
+
+import org.openjdk.jmh.annotations.Benchmark;
+import org.openjdk.jmh.annotations.Scope;
+import org.openjdk.jmh.annotations.State;
+
+@State(Scope.Benchmark)
+public class FalseSharing {
+
+    private java.util.concurrent.atomic.LongAdder builtin = new java.util.concurrent.atomic.LongAdder();
+    private LongAdder custom = new LongAdder();
+
+    @Benchmark
+    public void builtin() {
+        builtin.increment();
+    }
+
+    @Benchmark
+    public void custom() {
+        custom.increment();
+    }
+}

jmh/src/main/java/com/baeldung/falsesharing/LongAdder.java

@@ -0,0 +1,237 @@
+package com.baeldung.falsesharing;
+
+import java.io.Serializable;
+import java.util.concurrent.atomic.AtomicLong;
+
+/**
+ * Copy-pasted from {@link java.util.concurrent.atomic.LongAdder}
+ *
+ * One or more variables that together maintain an initially zero
+ * {@code long} sum.  When updates (method {@link #add}) are contended
+ * across threads, the set of variables may grow dynamically to reduce
+ * contention. Method {@link #sum} (or, equivalently, {@link
+ * #longValue}) returns the current total combined across the
+ * variables maintaining the sum.
+ *
+ * <p>This class is usually preferable to {@link AtomicLong} when
+ * multiple threads update a common sum that is used for purposes such
+ * as collecting statistics, not for fine-grained synchronization
+ * control.  Under low update contention, the two classes have similar
+ * characteristics. But under high contention, expected throughput of
+ * this class is significantly higher, at the expense of higher space
+ * consumption.
+ *
+ * <p>LongAdders can be used with a {@link
+ * java.util.concurrent.ConcurrentHashMap} to maintain a scalable
+ * frequency map (a form of histogram or multiset). For example, to
+ * add a count to a {@code ConcurrentHashMap<String,LongAdder> freqs},
+ * initializing if not already present, you can use {@code
+ * freqs.computeIfAbsent(k -> new LongAdder()).increment();}
+ *
+ * <p>This class extends {@link Number}, but does <em>not</em> define
+ * methods such as {@code equals}, {@code hashCode} and {@code
+ * compareTo} because instances are expected to be mutated, and so are
+ * not useful as collection keys.
+ *
+ * @since 1.8
+ * @author Doug Lea
+ */
+public class LongAdder extends Striped64 implements Serializable {
+    private static final long serialVersionUID = 7249069246863182397L;
+
+    /**
+     * Creates a new adder with initial sum of zero.
+     */
+    public LongAdder() {
+    }
+
+    /**
+     * Adds the given value.
+     *
+     * @param x the value to add
+     */
+    public void add(long x) {
+        Cell[] as; long b, v; int m; Cell a;
+        if ((as = cells) != null || !casBase(b = base, b + x)) {
+            boolean uncontended = true;
+            if (as == null || (m = as.length - 1) < 0 ||
+              (a = as[getProbe() & m]) == null ||
+              !(uncontended = a.cas(v = a.value, v + x)))
+                longAccumulate(x, null, uncontended);
+        }
+    }
+
+    /**
+     * Equivalent to {@code add(1)}.
+     */
+    public void increment() {
+        add(1L);
+    }
+
+    /**
+     * Equivalent to {@code add(-1)}.
+     */
+    public void decrement() {
+        add(-1L);
+    }
+
+    /**
+     * Returns the current sum.  The returned value is <em>NOT</em> an
+     * atomic snapshot; invocation in the absence of concurrent
+     * updates returns an accurate result, but concurrent updates that
+     * occur while the sum is being calculated might not be
+     * incorporated.
+     *
+     * @return the sum
+     */
+    public long sum() {
+        Cell[] as = cells; Cell a;
+        long sum = base;
+        if (as != null) {
+            for (int i = 0; i < as.length; ++i) {
+                if ((a = as[i]) != null)
+                    sum += a.value;
+            }
+        }
+        return sum;
+    }
+
+    /**
+     * Resets variables maintaining the sum to zero.  This method may
+     * be a useful alternative to creating a new adder, but is only
+     * effective if there are no concurrent updates.  Because this
+     * method is intrinsically racy, it should only be used when it is
+     * known that no threads are concurrently updating.
+     */
+    public void reset() {
+        Cell[] as = cells; Cell a;
+        base = 0L;
+        if (as != null) {
+            for (int i = 0; i < as.length; ++i) {
+                if ((a = as[i]) != null)
+                    a.value = 0L;
+            }
+        }
+    }
+
+    /**
+     * Equivalent in effect to {@link #sum} followed by {@link
+     * #reset}. This method may apply for example during quiescent
+     * points between multithreaded computations.  If there are
+     * updates concurrent with this method, the returned value is
+     * <em>not</em> guaranteed to be the final value occurring before
+     * the reset.
+     *
+     * @return the sum
+     */
+    public long sumThenReset() {
+        Cell[] as = cells; Cell a;
+        long sum = base;
+        base = 0L;
+        if (as != null) {
+            for (int i = 0; i < as.length; ++i) {
+                if ((a = as[i]) != null) {
+                    sum += a.value;
+                    a.value = 0L;
+                }
+            }
+        }
+        return sum;
+    }
+
+    /**
+     * Returns the String representation of the {@link #sum}.
+     * @return the String representation of the {@link #sum}
+     */
+    public String toString() {
+        return Long.toString(sum());
+    }
+
+    /**
+     * Equivalent to {@link #sum}.
+     *
+     * @return the sum
+     */
+    public long longValue() {
+        return sum();
+    }
+
+    /**
+     * Returns the {@link #sum} as an {@code int} after a narrowing
+     * primitive conversion.
+     */
+    public int intValue() {
+        return (int)sum();
+    }
+
+    /**
+     * Returns the {@link #sum} as a {@code float}
+     * after a widening primitive conversion.
+     */
+    public float floatValue() {
+        return (float)sum();
+    }
+
+    /**
+     * Returns the {@link #sum} as a {@code double} after a widening
+     * primitive conversion.
+     */
+    public double doubleValue() {
+        return (double)sum();
+    }
+
+    /**
+     * Serialization proxy, used to avoid reference to the non-public
+     * Striped64 superclass in serialized forms.
+     * @serial include
+     */
+    private static class SerializationProxy implements Serializable {
+        private static final long serialVersionUID = 7249069246863182397L;
+
+        /**
+         * The current value returned by sum().
+         * @serial
+         */
+        private final long value;
+
+        SerializationProxy(LongAdder a) {
+            value = a.sum();
+        }
+
+        /**
+         * Return a {@code LongAdder} object with initial state
+         * held by this proxy.
+         *
+         * @return a {@code LongAdder} object with initial state
+         * held by this proxy.
+         */
+        private Object readResolve() {
+            LongAdder a = new LongAdder();
+            a.base = value;
+            return a;
+        }
+    }
+
+    /**
+     * Returns a
+     * <a href="../../../../serialized-form.html#java.util.concurrent.atomic.LongAdder.SerializationProxy">
+     * SerializationProxy</a>
+     * representing the state of this instance.
+     *
+     * @return a {@link SerializationProxy}
+     * representing the state of this instance
+     */
+    private Object writeReplace() {
+        return new SerializationProxy(this);
+    }
+
+    /**
+     * @param s the stream
+     * @throws java.io.InvalidObjectException always
+     */
+    private void readObject(java.io.ObjectInputStream s)
+      throws java.io.InvalidObjectException {
+        throw new java.io.InvalidObjectException("Proxy required");
+    }
+
+}

jmh/src/main/java/com/baeldung/falsesharing/Striped64.java

@@ -0,0 +1,395 @@
+package com.baeldung.falsesharing;
+
+import sun.misc.Unsafe;
+
+import java.lang.reflect.Field;
+import java.util.function.LongBinaryOperator;
+import java.util.function.DoubleBinaryOperator;
+import java.util.concurrent.ThreadLocalRandom;
+
+/**
+ * Copy-pasted from {@code java.util.concurrent.atomic.Striped64} class.
+ *
+ * A package-local class holding common representation and mechanics
+ * for classes supporting dynamic striping on 64bit values. The class
+ * extends Number so that concrete subclasses must publicly do so.
+ */
+@SuppressWarnings("serial")
+abstract class Striped64 extends Number {
+    /*
+     * This class maintains a lazily-initialized table of atomically
+     * updated variables, plus an extra "base" field. The table size
+     * is a power of two. Indexing uses masked per-thread hash codes.
+     * Nearly all declarations in this class are package-private,
+     * accessed directly by subclasses.
+     *
+     * Table entries are of class Cell; a variant of AtomicLong padded
+     * (via @sun.misc.Contended) to reduce cache contention. Padding
+     * is overkill for most Atomics because they are usually
+     * irregularly scattered in memory and thus don't interfere much
+     * with each other. But Atomic objects residing in arrays will
+     * tend to be placed adjacent to each other, and so will most
+     * often share cache lines (with a huge negative performance
+     * impact) without this precaution.
+     *
+     * In part because Cells are relatively large, we avoid creating
+     * them until they are needed.  When there is no contention, all
+     * updates are made to the base field.  Upon first contention (a
+     * failed CAS on base update), the table is initialized to size 2.
+     * The table size is doubled upon further contention until
+     * reaching the nearest power of two greater than or equal to the
+     * number of CPUS. Table slots remain empty (null) until they are
+     * needed.
+     *
+     * A single spinlock ("cellsBusy") is used for initializing and
+     * resizing the table, as well as populating slots with new Cells.
+     * There is no need for a blocking lock; when the lock is not
+     * available, threads try other slots (or the base).  During these
+     * retries, there is increased contention and reduced locality,
+     * which is still better than alternatives.
+     *
+     * The Thread probe fields maintained via ThreadLocalRandom serve
+     * as per-thread hash codes. We let them remain uninitialized as
+     * zero (if they come in this way) until they contend at slot
+     * 0. They are then initialized to values that typically do not
+     * often conflict with others.  Contention and/or table collisions
+     * are indicated by failed CASes when performing an update
+     * operation. Upon a collision, if the table size is less than
+     * the capacity, it is doubled in size unless some other thread
+     * holds the lock. If a hashed slot is empty, and lock is
+     * available, a new Cell is created. Otherwise, if the slot
+     * exists, a CAS is tried.  Retries proceed by "double hashing",
+     * using a secondary hash (Marsaglia XorShift) to try to find a
+     * free slot.
+     *
+     * The table size is capped because, when there are more threads
+     * than CPUs, supposing that each thread were bound to a CPU,
+     * there would exist a perfect hash function mapping threads to
+     * slots that eliminates collisions. When we reach capacity, we
+     * search for this mapping by randomly varying the hash codes of
+     * colliding threads.  Because search is random, and collisions
+     * only become known via CAS failures, convergence can be slow,
+     * and because threads are typically not bound to CPUS forever,
+     * may not occur at all. However, despite these limitations,
+     * observed contention rates are typically low in these cases.
+     *
+     * It is possible for a Cell to become unused when threads that
+     * once hashed to it terminate, as well as in the case where
+     * doubling the table causes no thread to hash to it under
+     * expanded mask.  We do not try to detect or remove such cells,
+     * under the assumption that for long-running instances, observed
+     * contention levels will recur, so the cells will eventually be
+     * needed again; and for short-lived ones, it does not matter.
+     */
+
+    /**
+     * Padded variant of AtomicLong supporting only raw accesses plus CAS.
+     *
+     * JVM intrinsics note: It would be possible to use a release-only
+     * form of CAS here, if it were provided.
+     */
+    @sun.misc.Contended static final class Cell {
+        volatile long value;
+        Cell(long x) { value = x; }
+        final boolean cas(long cmp, long val) {
+            return UNSAFE.compareAndSwapLong(this, valueOffset, cmp, val);
+        }
+
+        // Unsafe mechanics
+        private static final sun.misc.Unsafe UNSAFE;
+        private static final long valueOffset;
+        static {
+            try {
+                UNSAFE = getUnsafe();
+                Class<?> ak = Striped64.Cell.class;
+                valueOffset = UNSAFE.objectFieldOffset
+                  (ak.getDeclaredField("value"));
+            } catch (Exception e) {
+                throw new Error(e);
+            }
+        }
+    }
+
+    /** Number of CPUS, to place bound on table size */
+    static final int NCPU = Runtime.getRuntime().availableProcessors();
+
+    /**
+     * Table of cells. When non-null, size is a power of 2.
+     */
+    transient volatile Striped64.Cell[] cells;
+
+    /**
+     * Base value, used mainly when there is no contention, but also as
+     * a fallback during table initialization races. Updated via CAS.
+     */
+    transient volatile long base;
+
+    /**
+     * Spinlock (locked via CAS) used when resizing and/or creating Cells.
+     */
+    transient volatile int cellsBusy;
+
+    /**
+     * Package-private default constructor
+     */
+    Striped64() {
+    }
+
+    /**
+     * CASes the base field.
+     */
+    final boolean casBase(long cmp, long val) {
+        return UNSAFE.compareAndSwapLong(this, BASE, cmp, val);
+    }
+
+    /**
+     * CASes the cellsBusy field from 0 to 1 to acquire lock.
+     */
+    final boolean casCellsBusy() {
+        return UNSAFE.compareAndSwapInt(this, CELLSBUSY, 0, 1);
+    }
+
+    /**
+     * Returns the probe value for the current thread.
+     * Duplicated from ThreadLocalRandom because of packaging restrictions.
+     */
+    static final int getProbe() {
+        return UNSAFE.getInt(Thread.currentThread(), PROBE);
+    }
+
+    /**
+     * Pseudo-randomly advances and records the given probe value for the
+     * given thread.
+     * Duplicated from ThreadLocalRandom because of packaging restrictions.
+     */
+    static final int advanceProbe(int probe) {
+        probe ^= probe << 13;   // xorshift
+        probe ^= probe >>> 17;
+        probe ^= probe << 5;
+        UNSAFE.putInt(Thread.currentThread(), PROBE, probe);
+        return probe;
+    }
+
+    /**
+     * Handles cases of updates involving initialization, resizing,
+     * creating new Cells, and/or contention. See above for
+     * explanation. This method suffers the usual non-modularity
+     * problems of optimistic retry code, relying on rechecked sets of
+     * reads.
+     *
+     * @param x the value
+     * @param fn the update function, or null for add (this convention
+     * avoids the need for an extra field or function in LongAdder).
+     * @param wasUncontended false if CAS failed before call
+     */
+    final void longAccumulate(long x, LongBinaryOperator fn,
+      boolean wasUncontended) {
+        int h;
+        if ((h = getProbe()) == 0) {
+            ThreadLocalRandom.current(); // force initialization
+            h = getProbe();
+            wasUncontended = true;
+        }
+        boolean collide = false;                // True if last slot nonempty
+        for (;;) {
+            Striped64.Cell[] as; Striped64.Cell a; int n; long v;
+            if ((as = cells) != null && (n = as.length) > 0) {
+                if ((a = as[(n - 1) & h]) == null) {
+                    if (cellsBusy == 0) {       // Try to attach new Cell
+                        Striped64.Cell r = new Striped64.Cell(x);   // Optimistically create
+                        if (cellsBusy == 0 && casCellsBusy()) {
+                            boolean created = false;
+                            try {               // Recheck under lock
+                                Striped64.Cell[] rs; int m, j;
+                                if ((rs = cells) != null &&
+                                  (m = rs.length) > 0 &&
+                                  rs[j = (m - 1) & h] == null) {
+                                    rs[j] = r;
+                                    created = true;
+                                }
+                            } finally {
+                                cellsBusy = 0;
+                            }
+                            if (created)
+                                break;
+                            continue;           // Slot is now non-empty
+                        }
+                    }
+                    collide = false;
+                }
+                else if (!wasUncontended)       // CAS already known to fail
+                    wasUncontended = true;      // Continue after rehash
+                else if (a.cas(v = a.value, ((fn == null) ? v + x :
+                  fn.applyAsLong(v, x))))
+                    break;
+                else if (n >= NCPU || cells != as)
+                    collide = false;            // At max size or stale
+                else if (!collide)
+                    collide = true;
+                else if (cellsBusy == 0 && casCellsBusy()) {
+                    try {
+                        if (cells == as) {      // Expand table unless stale
+                            Striped64.Cell[] rs = new Striped64.Cell[n << 1];
+                            for (int i = 0; i < n; ++i)
+                                rs[i] = as[i];
+                            cells = rs;
+                        }
+                    } finally {
+                        cellsBusy = 0;
+                    }
+                    collide = false;
+                    continue;                   // Retry with expanded table
+                }
+                h = advanceProbe(h);
+            }
+            else if (cellsBusy == 0 && cells == as && casCellsBusy()) {
+                boolean init = false;
+                try {                           // Initialize table
+                    if (cells == as) {
+                        Striped64.Cell[] rs = new Striped64.Cell[2];
+                        rs[h & 1] = new Striped64.Cell(x);
+                        cells = rs;
+                        init = true;
+                    }
+                } finally {
+                    cellsBusy = 0;
+                }
+                if (init)
+                    break;
+            }
+            else if (casBase(v = base, ((fn == null) ? v + x :
+              fn.applyAsLong(v, x))))
+                break;                          // Fall back on using base
+        }
+    }
+
+    /**
+     * Same as longAccumulate, but injecting long/double conversions
+     * in too many places to sensibly merge with long version, given
+     * the low-overhead requirements of this class. So must instead be
+     * maintained by copy/paste/adapt.
+     */
+    final void doubleAccumulate(double x, DoubleBinaryOperator fn,
+      boolean wasUncontended) {
+        int h;
+        if ((h = getProbe()) == 0) {
+            ThreadLocalRandom.current(); // force initialization
+            h = getProbe();
+            wasUncontended = true;
+        }
+        boolean collide = false;                // True if last slot nonempty
+        for (;;) {
+            Striped64.Cell[] as; Striped64.Cell a; int n; long v;
+            if ((as = cells) != null && (n = as.length) > 0) {
+                if ((a = as[(n - 1) & h]) == null) {
+                    if (cellsBusy == 0) {       // Try to attach new Cell
+                        Striped64.Cell r = new Striped64.Cell(Double.doubleToRawLongBits(x));
+                        if (cellsBusy == 0 && casCellsBusy()) {
+                            boolean created = false;
+                            try {               // Recheck under lock
+                                Striped64.Cell[] rs; int m, j;
+                                if ((rs = cells) != null &&
+                                  (m = rs.length) > 0 &&
+                                  rs[j = (m - 1) & h] == null) {
+                                    rs[j] = r;
+                                    created = true;
+                                }
+                            } finally {
+                                cellsBusy = 0;
+                            }
+                            if (created)
+                                break;
+                            continue;           // Slot is now non-empty
+                        }
+                    }
+                    collide = false;
+                }
+                else if (!wasUncontended)       // CAS already known to fail
+                    wasUncontended = true;      // Continue after rehash
+                else if (a.cas(v = a.value,
+                  ((fn == null) ?
+                    Double.doubleToRawLongBits
+                      (Double.longBitsToDouble(v) + x) :
+                    Double.doubleToRawLongBits
+                      (fn.applyAsDouble
+                        (Double.longBitsToDouble(v), x)))))
+                    break;
+                else if (n >= NCPU || cells != as)
+                    collide = false;            // At max size or stale
+                else if (!collide)
+                    collide = true;
+                else if (cellsBusy == 0 && casCellsBusy()) {
+                    try {
+                        if (cells == as) {      // Expand table unless stale
+                            Striped64.Cell[] rs = new Striped64.Cell[n << 1];
+                            for (int i = 0; i < n; ++i)
+                                rs[i] = as[i];
+                            cells = rs;
+                        }
+                    } finally {
+                        cellsBusy = 0;
+                    }
+                    collide = false;
+                    continue;                   // Retry with expanded table
+                }
+                h = advanceProbe(h);
+            }
+            else if (cellsBusy == 0 && cells == as && casCellsBusy()) {
+                boolean init = false;
+                try {                           // Initialize table
+                    if (cells == as) {
+                        Striped64.Cell[] rs = new Striped64.Cell[2];
+                        rs[h & 1] = new Striped64.Cell(Double.doubleToRawLongBits(x));
+                        cells = rs;
+                        init = true;
+                    }
+                } finally {
+                    cellsBusy = 0;
+                }
+                if (init)
+                    break;
+            }
+            else if (casBase(v = base,
+              ((fn == null) ?
+                Double.doubleToRawLongBits
+                  (Double.longBitsToDouble(v) + x) :
+                Double.doubleToRawLongBits
+                  (fn.applyAsDouble
+                    (Double.longBitsToDouble(v), x)))))
+                break;                          // Fall back on using base
+        }
+    }
+
+    // Unsafe mechanics
+    private static final sun.misc.Unsafe UNSAFE;
+    private static final long BASE;
+    private static final long CELLSBUSY;
+    private static final long PROBE;
+    static {
+        try {
+            UNSAFE = getUnsafe();
+            Class<?> sk = Striped64.class;
+            BASE = UNSAFE.objectFieldOffset
+              (sk.getDeclaredField("base"));
+            CELLSBUSY = UNSAFE.objectFieldOffset
+              (sk.getDeclaredField("cellsBusy"));
+            Class<?> tk = Thread.class;
+            PROBE = UNSAFE.objectFieldOffset
+              (tk.getDeclaredField("threadLocalRandomProbe"));
+        } catch (Exception e) {
+            throw new Error(e);
+        }
+    }
+
+    private static Unsafe getUnsafe() {
+        try {
+            Field field = Unsafe.class.getDeclaredField("theUnsafe");
+            field.setAccessible(true);
+
+            return (Unsafe) field.get(null);
+        } catch (Exception e) {
+            throw new RuntimeException(e);
+        }
+    }
+
+}

libraries-6/README.md

@@ -15,4 +15,5 @@ Remember, for advanced libraries like [Jackson](/jackson) and [JUnit](/testing-m
 - [A Guide to the Reflections Library](https://www.baeldung.com/reflections-library)
 - [Exactly Once Processing in Kafka](https://www.baeldung.com/kafka-exactly-once)
 - [Introduction to Protonpack](https://www.baeldung.com/java-protonpack)
+- [Java-R Integration](https://www.baeldung.com/java-r-integration)
 - More articles [[<-- prev]](/libraries-5)

libraries-6/pom.xml

@@ -92,8 +92,50 @@
             <version>${commonsio.version}</version>
             <scope>test</scope>
         </dependency>
+        <dependency>
+            <groupId>org.rosuda.REngine</groupId>
+            <artifactId>Rserve</artifactId>
+            <version>${rserve.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>com.github.jbytecode</groupId>
+            <artifactId>RCaller</artifactId>
+            <version>${rcaller.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.renjin</groupId>
+            <artifactId>renjin-script-engine</artifactId>
+            <version>${renjin.version}</version>
+        </dependency>
     </dependencies>
 
+    <repositories>
+        <!-- Needed for Renjin -->
+        <repository>
+            <id>bedatadriven</id>
+            <name>bedatadriven public repo</name>
+            <url>https://nexus.bedatadriven.com/content/groups/public/</url>
+        </repository>
+    </repositories>
+
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-compiler-plugin</artifactId>
+                <configuration>
+                    <!-- Excludes FastR classes from compilations since they require GraalVM -->
+                    <excludes>
+                        <exclude>com/baeldung/r/FastRMean.java</exclude>
+                    </excludes>
+                    <testExcludes>
+                        <exclude>com/baeldung/r/FastRMeanUnitTest.java</exclude>
+                    </testExcludes>
+                </configuration>
+            </plugin>
+        </plugins>
+    </build>
+
     <properties>
         <kafka.version>2.0.0</kafka.version>
         <javapoet.version>1.10.0</javapoet.version>
@@ -105,6 +147,9 @@
         <commons-net.version>3.6</commons-net.version>
         <assertj.version>3.6.2</assertj.version>
         <commonsio.version>2.6</commonsio.version>
+        <renjin.version>RELEASE</renjin.version>
+        <rcaller.version>3.0</rcaller.version>
+        <rserve.version>1.8.1</rserve.version>
     </properties>
 
 

libraries-6/src/main/java/com/baeldung/r/FastRMean.java

@@ -1,8 +1,5 @@
 package com.baeldung.r;
 
-import java.io.IOException;
-import java.net.URISyntaxException;
-
 /**
  * FastR showcase.
  * 

libraries-6/src/main/java/com/baeldung/r/RCallerMean.java

@@ -1,12 +1,12 @@
 package com.baeldung.r;
 
-import java.io.IOException;
-import java.net.URISyntaxException;
-
 import com.github.rcaller.rstuff.RCaller;
 import com.github.rcaller.rstuff.RCallerOptions;
 import com.github.rcaller.rstuff.RCode;
 
+import java.io.IOException;
+import java.net.URISyntaxException;
+
 /**
  * RCaller showcase.
  * 

libraries-6/src/main/java/com/baeldung/r/RenjinMean.java

@@ -1,13 +1,12 @@
 package com.baeldung.r;
 
-import java.io.IOException;
-import java.net.URISyntaxException;
-
-import javax.script.ScriptException;
-
 import org.renjin.script.RenjinScriptEngine;
 import org.renjin.sexp.DoubleArrayVector;
 
+import javax.script.ScriptException;
+import java.io.IOException;
+import java.net.URISyntaxException;
+
 /**
  * Renjin showcase.
  * 

libraries-6/src/test/java/com/baeldung/r/RCallerMeanIntegrationTest.java

@@ -1,14 +1,13 @@
 package com.baeldung.r;
 
-import java.io.IOException;
-import java.net.URISyntaxException;
-
-import javax.script.ScriptException;
-
 import org.junit.Assert;
 import org.junit.Ignore;
 import org.junit.Test;
 
+import javax.script.ScriptException;
+import java.io.IOException;
+import java.net.URISyntaxException;
+
 /**
  * Test for {@link RCallerMean}.
  * 

libraries-6/src/test/java/com/baeldung/r/RenjinMeanUnitTest.java

@@ -1,13 +1,11 @@
 package com.baeldung.r;
 
-import java.io.IOException;
-import java.net.URISyntaxException;
-
-import javax.script.ScriptException;
-
+import org.junit.Assert;
 import org.junit.Test;
 
-import org.junit.Assert;
+import javax.script.ScriptException;
+import java.io.IOException;
+import java.net.URISyntaxException;
 
 /**
  * Test for {@link RenjinMean}.

libraries-apache-commons/README.md

@@ -13,3 +13,4 @@ This module contains articles about Apache Commons libraries.
 - [Apache Commons BeanUtils](https://www.baeldung.com/apache-commons-beanutils)
 - [Histograms with Apache Commons Frequency](https://www.baeldung.com/apache-commons-frequency)
 - [An Introduction to Apache Commons Lang 3](https://www.baeldung.com/java-commons-lang-3)
+- [Differences Between the Java WatchService API and the Apache Commons IO Monitor Library](https://www.baeldung.com/java-watchservice-vs-apache-commons-io-monitor-library)

libraries-apache-commons/pom.xml

@@ -57,6 +57,11 @@
             <artifactId>xchart</artifactId>
             <version>${xchart-version}</version>
         </dependency>
+        <dependency>
+            <groupId>commons-io</groupId>
+            <artifactId>commons-io</artifactId>
+            <version>${common-io.version}</version>
+        </dependency>
     </dependencies>
 
     <properties>
@@ -68,6 +73,7 @@
         <commons.dbutils.version>1.6</commons.dbutils.version>
         <xchart-version>3.5.2</xchart-version>
         <common-math3.version>3.6.1</common-math3.version>
+        <common-io.version>2.5</common-io.version>
     </properties>
 
 </project>

libraries-data-2/README.md

@@ -8,10 +8,8 @@ This module contains articles about libraries for data processing in Java.
 - [Introduction to Conflict-Free Replicated Data Types](https://www.baeldung.com/java-conflict-free-replicated-data-types)
 - [Introduction to javax.measure](https://www.baeldung.com/javax-measure)
 - [A Guide to Infinispan in Java](https://www.baeldung.com/infinispan)
-- [Guide to JMapper](https://www.baeldung.com/jmapper)
 - [An Introduction to SuanShu](https://www.baeldung.com/suanshu)
 - [Intro to Derive4J](https://www.baeldung.com/derive4j)
-- [Java-R Integration](https://www.baeldung.com/java-r-integration)
 - [Univocity Parsers](https://www.baeldung.com/java-univocity-parsers)
 - [Using Kafka MockConsumer](https://www.baeldung.com/kafka-mockconsumer)
 - [Using Kafka MockProducer](https://www.baeldung.com/kafka-mockproducer)

libraries-data-2/pom.xml

@@ -86,11 +86,6 @@
             <artifactId>spring-web</artifactId>
             <version>${spring.version}</version>
         </dependency>
-        <dependency>
-            <groupId>com.googlecode.jmapper-framework</groupId>
-            <artifactId>jmapper-core</artifactId>
-            <version>${jmapper.version}</version>
-        </dependency>
         <dependency>
             <groupId>com.numericalmethod</groupId>
             <artifactId>suanshu</artifactId>
@@ -126,6 +121,11 @@
             <artifactId>kafka-clients</artifactId>
             <version>${kafka.version}</version>
         </dependency>
+        <dependency>
+            <groupId>com.google.guava</groupId>
+            <artifactId>guava</artifactId>
+            <version>${guava.version}</version>
+        </dependency>
         <dependency>
             <groupId>org.awaitility</groupId>
             <artifactId>awaitility</artifactId>
@@ -138,21 +138,6 @@
             <version>${awaitility.version}</version>
             <scope>test</scope>
         </dependency>
-        <dependency>
-            <groupId>org.rosuda.REngine</groupId>
-            <artifactId>Rserve</artifactId>
-            <version>${rserve.version}</version>
-        </dependency>
-        <dependency>
-            <groupId>com.github.jbytecode</groupId>
-            <artifactId>RCaller</artifactId>
-            <version>${rcaller.version}</version>
-        </dependency>
-        <dependency>
-            <groupId>org.renjin</groupId>
-            <artifactId>renjin-script-engine</artifactId>
-            <version>${renjin.version}</version>
-        </dependency>
         <dependency>
             <groupId>net.bytebuddy</groupId>
             <artifactId>byte-buddy</artifactId>
@@ -175,33 +160,8 @@
             <url>http://repo.numericalmethod.com/maven/</url>
             <layout>default</layout>
         </repository>
-        
-        <!-- Needed for Renjin -->
-        <repository>
-            <id>bedatadriven</id>
-            <name>bedatadriven public repo</name>
-            <url>https://nexus.bedatadriven.com/content/groups/public/</url>
-        </repository>
     </repositories>
 
-    <build>
-        <plugins>
-            <plugin>
-                <groupId>org.apache.maven.plugins</groupId>
-                <artifactId>maven-compiler-plugin</artifactId>
-                <configuration>
-                    <!-- Excludes FastR classes from compilations since they require GraalVM -->
-                    <excludes>
-                        <exclude>com/baeldung/r/FastRMean.java</exclude>
-                    </excludes>
-                    <testExcludes>
-                        <exclude>com/baeldung/r/FastRMeanUnitTest.java</exclude>						
-                    </testExcludes>
-                </configuration>
-            </plugin>
-        </plugins>
-    </build>
-
     <properties>
         <flink.version>1.5.0</flink.version>
         <hll.version>1.6.0</hll.version>
@@ -210,17 +170,14 @@
         <infinispan.version>9.1.5.Final</infinispan.version>
         <jackson.version>2.9.8</jackson.version>
         <spring.version>4.3.8.RELEASE</spring.version>
-        <jmapper.version>1.6.0.1</jmapper.version>
         <suanshu.version>4.0.0</suanshu.version>
         <derive4j.version>1.1.0</derive4j.version>
         <assertj.version>3.6.2</assertj.version>
         <slf4j.version>1.7.25</slf4j.version>
         <awaitility.version>3.0.0</awaitility.version>
         <univocity.version>2.8.4</univocity.version>
-        <renjin.version>RELEASE</renjin.version>
-        <rcaller.version>3.0</rcaller.version>
-        <rserve.version>1.8.1</rserve.version>
         <kafka.version>2.5.0</kafka.version>
+        <guava.version>29.0-jre</guava.version>
     </properties>
 
 </project>

libraries-data/README.md

@@ -12,4 +12,5 @@ This module contains articles about libraries for data processing in Java.
 - [Introduction to Kafka Connectors](https://www.baeldung.com/kafka-connectors-guide)
 - [Kafka Connect Example with MQTT and MongoDB](https://www.baeldung.com/kafka-connect-mqtt-mongodb)
 - [Building a Data Pipeline with Flink and Kafka](https://www.baeldung.com/kafka-flink-data-pipeline)
+- [Guide to JMapper](https://www.baeldung.com/jmapper)
 More articles: [[next -->]](/../libraries-data-2)

libraries-data/pom.xml

@@ -126,6 +126,11 @@
                 </exclusion>
             </exclusions>
         </dependency>
+        <dependency>
+            <groupId>com.googlecode.jmapper-framework</groupId>
+            <artifactId>jmapper-core</artifactId>
+            <version>${jmapper.version}</version>
+        </dependency>
     </dependencies>
 
     <build>
@@ -172,6 +177,7 @@
         <org.apache.crunch.crunch-core.version>0.15.0</org.apache.crunch.crunch-core.version>
         <org.apache.hadoop.hadoop-client>2.2.0</org.apache.hadoop.hadoop-client>
         <slf4j.version>1.7.25</slf4j.version>
+        <jmapper.version>1.6.0.1</jmapper.version>
     </properties>
 
 </project>

libraries-data/src/test/java/com/baeldung/jmapper/JMapperIntegrationTest.java

@@ -7,6 +7,9 @@ import org.junit.Test;
 import java.time.LocalDate;
 
 import static com.googlecode.jmapper.api.JMapperAPI.*;
+import static com.googlecode.jmapper.api.JMapperAPI.attribute;
+import static com.googlecode.jmapper.api.JMapperAPI.global;
+import static com.googlecode.jmapper.api.JMapperAPI.mappedClass;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertTrue;
 

libraries-data/src/test/java/com/baeldung/jmapper/JMapperRelationalIntegrationTest.java

@@ -55,8 +55,8 @@ public class JMapperRelationalIntegrationTest {
     public void givenUser_whenUseApi_thenConverted(){
         JMapperAPI jmapperApi = new JMapperAPI() 
         .add(mappedClass(User.class)
-            .add(attribute("id").value("id").targetClasses(UserDto1.class,UserDto2.class))
-            .add(attribute("email").targetAttributes("username","email").targetClasses(UserDto1.class,UserDto2.class)) )
+            .add(attribute("id").value("id").targetClasses(UserDto1.class, UserDto2.class))
+            .add(attribute("email").targetAttributes("username","email").targetClasses(UserDto1.class, UserDto2.class)) )
          ;
         RelationalJMapper<User> relationalMapper = new RelationalJMapper<>(User.class,jmapperApi);
         

libraries-security/README.md

@@ -10,3 +10,4 @@ This module contains articles about security libraries.
 - [Introduction to BouncyCastle with Java](https://www.baeldung.com/java-bouncy-castle)
 - [Intro to Jasypt](https://www.baeldung.com/jasypt)
 - [Digital Signatures in Java](https://www.baeldung.com/java-digital-signature)
+- [How to Read PEM File to Get Public and Private Keys](https://www.baeldung.com/java-read-pem-file-keys)

linux-bash/text/README.md

@@ -1,4 +1,4 @@
 ### Relevant Articles:
 
-- [Linux Commands – Remove All Text After X](https://www.baeldung.com/linux/tr-manipulate-strings)
+- [Linux Commands – Remove All Text After X](https://www.baeldung.com/linux/remove-text-after-x-in-file)
 - [Linux Commands for Appending Multiple Lines to a File](https://www.baeldung.com/linux/appending-multiple-lines-to-file2)

mapstruct/README.md

@@ -8,3 +8,4 @@ This module contains articles about MapStruct.
 - [Custom Mapper with MapStruct](https://www.baeldung.com/mapstruct-custom-mapper)
 - [Using Multiple Source Objects with MapStruct](https://www.baeldung.com/mapstruct-multiple-source-objects)
 - [Ignoring Unmapped Properties with MapStruct](https://www.baeldung.com/mapstruct-ignore-unmapped-properties)
+- [Mapping Collections with MapStruct](https://www.baeldung.com/java-mapstruct-mapping-collections)