HADOOP-14901. ReuseObjectMapper in Hadoop Common. Contributed by Hanisha Koneru.

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/crypto/key/kms/KMSClientProvider.java

@@ -77,6 +77,7 @@
 import org.apache.hadoop.crypto.key.KeyProviderCryptoExtension.CryptoExtension;
 
 import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.ObjectWriter;
 import com.google.common.annotations.VisibleForTesting;
 import com.google.common.base.Preconditions;
 import com.google.common.base.Strings;
@@ -133,6 +134,9 @@ public class KMSClientProvider extends KeyProvider implements CryptoExtension,
 
   private final ValueQueue<EncryptedKeyVersion> encKeyVersionQueue;
 
+  private static final ObjectWriter WRITER =
+      new ObjectMapper().writerWithDefaultPrettyPrinter();
+
   private class EncryptedQueueRefiller implements
     ValueQueue.QueueRefiller<EncryptedKeyVersion> {
 
@@ -226,8 +230,7 @@ public KMSEncryptedKeyVersion(String keyName, String keyVersionName,
   private static void writeJson(Object obj, OutputStream os)
       throws IOException {
     Writer writer = new OutputStreamWriter(os, StandardCharsets.UTF_8);
-    ObjectMapper jsonMapper = new ObjectMapper();
+    WRITER.writeValue(writer, obj);
-    jsonMapper.writerWithDefaultPrettyPrinter().writeValue(writer, obj);
   }
 
   /**

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/ipc/DecayRpcScheduler.java

@@ -36,6 +36,7 @@
 import javax.management.ObjectName;
 
 import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.ObjectWriter;
 import com.google.common.base.Preconditions;
 import com.google.common.util.concurrent.AtomicDoubleArray;
 import org.apache.commons.lang.exception.ExceptionUtils;
@@ -128,6 +129,8 @@ public class DecayRpcScheduler implements RpcScheduler,
   public static final Logger LOG =
       LoggerFactory.getLogger(DecayRpcScheduler.class);
 
+  private static final ObjectWriter WRITER = new ObjectMapper().writer();
+
   // Track the decayed and raw (no decay) number of calls for each schedulable
   // identity from all previous decay windows: idx 0 for decayed call count and
   // idx 1 for the raw call count
@@ -909,8 +912,7 @@ public String getSchedulingDecisionSummary() {
       return "{}";
     } else {
       try {
-        ObjectMapper om = new ObjectMapper();
+        return WRITER.writeValueAsString(decisions);
-        return om.writeValueAsString(decisions);
       } catch (Exception e) {
         return "Error: " + e.getMessage();
       }
@@ -919,8 +921,7 @@ public String getSchedulingDecisionSummary() {
 
   public String getCallVolumeSummary() {
     try {
-      ObjectMapper om = new ObjectMapper();
+      return WRITER.writeValueAsString(getDecayedCallCounts());
-      return om.writeValueAsString(getDecayedCallCounts());
     } catch (Exception e) {
       return "Error: " + e.getMessage();
     }

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/log/Log4Json.java

@@ -24,6 +24,7 @@
 import com.fasterxml.jackson.databind.JsonNode;
 import com.fasterxml.jackson.databind.MappingJsonFactory;
 import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.ObjectReader;
 import com.fasterxml.jackson.databind.node.ContainerNode;
 import org.apache.log4j.Layout;
 import org.apache.log4j.helpers.ISO8601DateFormat;
@@ -105,6 +106,7 @@ public class Log4Json extends Layout {
    * configuration it must be done in a static intializer block.
    */
   private static final JsonFactory factory = new MappingJsonFactory();
+  private static final ObjectReader READER = new ObjectMapper(factory).reader();
   public static final String DATE = "date";
   public static final String EXCEPTION_CLASS = "exceptionclass";
   public static final String LEVEL = "level";
@@ -252,8 +254,7 @@ public void activateOptions() {
    * @throws IOException on any parsing problems
    */
   public static ContainerNode parse(String json) throws IOException {
-    ObjectMapper mapper = new ObjectMapper(factory);
+    JsonNode jsonNode = READER.readTree(json);
-    JsonNode jsonNode = mapper.readTree(json);
     if (!(jsonNode instanceof ContainerNode)) {
       throw new IOException("Wrong JSON data: " + json);
     }

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/metrics2/MetricsJsonBuilder.java

@@ -18,17 +18,18 @@
 
 package org.apache.hadoop.metrics2;
 
-import java.io.IOException;
-import java.util.LinkedHashMap;
-import java.util.Map;
-
 import org.apache.commons.lang.exception.ExceptionUtils;
 import org.apache.hadoop.classification.InterfaceAudience;
 import org.apache.hadoop.classification.InterfaceStability;
 import org.codehaus.jackson.map.ObjectMapper;
+import org.codehaus.jackson.map.ObjectWriter;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
+import java.io.IOException;
+import java.util.LinkedHashMap;
+import java.util.Map;
+
 /**
  * Build a JSON dump of the metrics.
  *
@@ -44,6 +45,9 @@ public class MetricsJsonBuilder extends MetricsRecordBuilder {
   private final MetricsCollector parent;
   private Map<String, Object> innerMetrics = new LinkedHashMap<>();
 
+  private static final ObjectWriter WRITER =
+      new ObjectMapper().writer();
+
   /**
    * Build an instance.
    * @param parent parent collector. Unused in this instance; only used for
@@ -116,7 +120,7 @@ public MetricsCollector parent() {
   @Override
   public String toString() {
     try {
-      return new ObjectMapper().writeValueAsString(innerMetrics);
+      return WRITER.writeValueAsString(innerMetrics);
     } catch (IOException e) {
       LOG.warn("Failed to dump to Json.", e);
       return ExceptionUtils.getStackTrace(e);

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/security/token/delegation/web/DelegationTokenAuthenticator.java

@@ -18,6 +18,7 @@
 package org.apache.hadoop.security.token.delegation.web;
 
 import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.ObjectReader;
 import org.apache.hadoop.classification.InterfaceAudience;
 import org.apache.hadoop.classification.InterfaceStability;
 import org.apache.hadoop.security.SecurityUtil;
@@ -54,6 +55,9 @@ public abstract class DelegationTokenAuthenticator implements Authenticator {
   private static final String CONTENT_TYPE = "Content-Type";
   private static final String APPLICATION_JSON_MIME = "application/json";
 
+  private static final ObjectReader READER =
+      new ObjectMapper().readerFor(Map.class);
+
   private static final String HTTP_GET = "GET";
   private static final String HTTP_PUT = "PUT";
 
@@ -316,8 +320,7 @@ private Map doDelegationTokenOperation(URL url,
         if (contentType != null &&
             contentType.contains(APPLICATION_JSON_MIME)) {
           try {
-            ObjectMapper mapper = new ObjectMapper();
+            ret = READER.readValue(conn.getInputStream());
-            ret = mapper.readValue(conn.getInputStream(), Map.class);
           } catch (Exception ex) {
             throw new AuthenticationException(String.format(
                 "'%s' did not handle the '%s' delegation token operation: %s",

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/util/HttpExceptionUtils.java

@@ -18,6 +18,8 @@
 package org.apache.hadoop.util;
 
 import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.ObjectReader;
+import com.fasterxml.jackson.databind.ObjectWriter;
 import org.apache.hadoop.classification.InterfaceAudience;
 import org.apache.hadoop.classification.InterfaceStability;
 
@@ -54,6 +56,11 @@ public class HttpExceptionUtils {
 
   private static final String ENTER = System.getProperty("line.separator");
 
+  private static final ObjectReader READER =
+      new ObjectMapper().readerFor(Map.class);
+  private static final ObjectWriter WRITER =
+      new ObjectMapper().writerWithDefaultPrettyPrinter();
+
   /**
    * Creates a HTTP servlet response serializing the exception in it as JSON.
    *
@@ -74,9 +81,8 @@ public static void createServletExceptionResponse(
     json.put(ERROR_CLASSNAME_JSON, ex.getClass().getName());
     Map<String, Object> jsonResponse = new LinkedHashMap<String, Object>();
     jsonResponse.put(ERROR_JSON, json);
-    ObjectMapper jsonMapper = new ObjectMapper();
     Writer writer = response.getWriter();
-    jsonMapper.writerWithDefaultPrettyPrinter().writeValue(writer, jsonResponse);
+    WRITER.writeValue(writer, jsonResponse);
     writer.flush();
   }
 
@@ -144,8 +150,7 @@ public static void validateResponse(HttpURLConnection conn,
       InputStream es = null;
       try {
         es = conn.getErrorStream();
-        ObjectMapper mapper = new ObjectMapper();
+        Map json = READER.readValue(es);
-        Map json = mapper.readValue(es, Map.class);
         json = (Map) json.get(ERROR_JSON);
         String exClass = (String) json.get(ERROR_CLASSNAME_JSON);
         String exMsg = (String) json.get(ERROR_MESSAGE_JSON);