HDFS-12064. Reuse object mapper in HDFS. Contributed by Hanisha Koneru.

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/SlowDiskTracker.java

@@ -22,6 +22,7 @@ import com.fasterxml.jackson.annotation.JsonIgnore;
 import com.fasterxml.jackson.annotation.JsonProperty;
 import com.fasterxml.jackson.core.JsonProcessingException;
 import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.ObjectWriter;
 import com.google.common.annotations.VisibleForTesting;
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.Lists;
@@ -67,6 +68,11 @@ public class SlowDiskTracker {
    */
   private final Timer timer;
 
+  /**
+   * ObjectWriter to convert JSON reports to String.
+   */
+  private static final ObjectWriter WRITER = new ObjectMapper().writer();
+
   /**
    * Number of disks to include in JSON report per operation. We will return
    * disks with the highest latency.
@@ -254,12 +260,11 @@ public class SlowDiskTracker {
    *         serialization failed.
    */
   public String getSlowDiskReportAsJsonString() {
-    ObjectMapper objectMapper = new ObjectMapper();
     try {
       if (slowDisksReport.isEmpty()) {
         return null;
       }
-      return objectMapper.writeValueAsString(slowDisksReport);
+      return WRITER.writeValueAsString(slowDisksReport);
     } catch (JsonProcessingException e) {
       // Failed to serialize. Don't log the exception call stack.
       LOG.debug("Failed to serialize statistics" + e);

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/SlowPeerTracker.java

@@ -21,6 +21,7 @@ package org.apache.hadoop.hdfs.server.blockmanagement;
 import com.fasterxml.jackson.annotation.JsonProperty;
 import com.fasterxml.jackson.core.JsonProcessingException;
 import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.ObjectWriter;
 import com.google.common.annotations.VisibleForTesting;
 import com.google.common.collect.ImmutableMap;
 import com.google.common.primitives.Ints;
@@ -69,6 +70,10 @@ public class SlowPeerTracker {
    */
   private final Timer timer;
 
+  /**
+   * ObjectWriter to convert JSON reports to String.
+   */
+  private static final ObjectWriter WRITER = new ObjectMapper().writer();
   /**
    * Number of nodes to include in JSON report. We will return nodes with
    * the highest number of votes from peers.
@@ -188,9 +193,8 @@ public class SlowPeerTracker {
   public String getJson() {
     Collection<ReportForJson> validReports = getJsonReports(
         MAX_NODES_TO_REPORT);
-    ObjectMapper objectMapper = new ObjectMapper();
     try {
-      return objectMapper.writeValueAsString(validReports);
+      return WRITER.writeValueAsString(validReports);
     } catch (JsonProcessingException e) {
       // Failed to serialize. Don't log the exception call stack.
       LOG.debug("Failed to serialize statistics" + e);

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/diskbalancer/planner/NodePlan.java

@@ -18,8 +18,9 @@
 package org.apache.hadoop.hdfs.server.diskbalancer.planner;
 
 import com.fasterxml.jackson.annotation.JsonTypeInfo;
-import com.fasterxml.jackson.databind.JavaType;
 import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.ObjectReader;
+import com.fasterxml.jackson.databind.ObjectWriter;
 import com.google.common.base.Preconditions;
 
 import java.io.IOException;
@@ -38,6 +39,10 @@ public class NodePlan {
   private int port;
   private long timeStamp;
 
+  private static final ObjectMapper MAPPER = new ObjectMapper();
+  private static final ObjectReader READER = MAPPER.readerFor(NodePlan.class);
+  private static final ObjectWriter WRITER = MAPPER.writerFor(
+      MAPPER.constructType(NodePlan.class));
   /**
    * returns timestamp when this plan was created.
    *
@@ -153,8 +158,7 @@ public class NodePlan {
    * @throws IOException
    */
   public static NodePlan parseJson(String json) throws IOException {
-    ObjectMapper mapper = new ObjectMapper();
-    return mapper.readValue(json, NodePlan.class);
+    return READER.readValue(json);
   }
 
   /**
@@ -164,10 +168,7 @@ public class NodePlan {
    * @throws IOException
    */
   public String toJson() throws IOException {
-    ObjectMapper mapper = new ObjectMapper();
-    JavaType planType = mapper.constructType(NodePlan.class);
-    return mapper.writerFor(planType)
-        .writeValueAsString(this);
+    return WRITER.writeValueAsString(this);
   }
 
   /**

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/blockmanagement/TestSlowDiskTracker.java

@@ -25,6 +25,7 @@ import static org.junit.Assert.assertTrue;
 
 import com.fasterxml.jackson.core.type.TypeReference;
 import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.ObjectReader;
 import com.google.common.collect.ImmutableMap;
 import org.apache.hadoop.conf.Configuration;
 import static org.apache.hadoop.hdfs.DFSConfigKeys
@@ -76,6 +77,8 @@ public class TestSlowDiskTracker {
   private FakeTimer timer;
   private long reportValidityMs;
   private static final long OUTLIERS_REPORT_INTERVAL = 1000;
+  private static final ObjectReader READER = new ObjectMapper().readerFor(
+          new TypeReference<ArrayList<DiskLatency>>() {});
 
   static {
     conf = new HdfsConfiguration();
@@ -416,8 +419,7 @@ public class TestSlowDiskTracker {
 
   private ArrayList<DiskLatency> getAndDeserializeJson(
       final String json) throws IOException {
-    return (new ObjectMapper()).readValue(json,
-        new TypeReference<ArrayList<DiskLatency>>() {});
+    return READER.readValue(json);
   }
 
   private void addSlowDiskForTesting(String dnID, String disk,

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/blockmanagement/TestSlowPeerTracker.java

@@ -20,9 +20,11 @@ package org.apache.hadoop.hdfs.server.blockmanagement;
 
 import com.fasterxml.jackson.core.type.TypeReference;
 import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.ObjectReader;
 import org.apache.hadoop.conf.Configuration;
 import org.apache.hadoop.hdfs.HdfsConfiguration;
-import org.apache.hadoop.hdfs.server.blockmanagement.SlowPeerTracker.ReportForJson;
+import org.apache.hadoop.hdfs.server.blockmanagement.SlowPeerTracker
+    .ReportForJson;
 import org.apache.hadoop.util.FakeTimer;
 import org.junit.Before;
 import org.junit.Rule;
@@ -39,7 +41,6 @@ import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertThat;
 import static org.junit.Assert.assertTrue;
 
-
 /**
  * Tests for {@link SlowPeerTracker}.
  */
@@ -57,6 +58,8 @@ public class TestSlowPeerTracker {
   private SlowPeerTracker tracker;
   private FakeTimer timer;
   private long reportValidityMs;
+  private static final ObjectReader READER =
+      new ObjectMapper().readerFor(new TypeReference<Set<ReportForJson>>() {});
 
   @Before
   public void setup() {
@@ -220,7 +223,6 @@ public class TestSlowPeerTracker {
       throws IOException {
     final String json = tracker.getJson();
     LOG.info("Got JSON: {}", json);
-    return (new ObjectMapper()).readValue(
-        json, new TypeReference<Set<ReportForJson>>() {});
+    return READER.readValue(json);
   }
 }

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/web/TestJsonUtil.java

@@ -52,6 +52,10 @@ import com.fasterxml.jackson.databind.ObjectReader;
 import com.google.common.collect.Lists;
 
 public class TestJsonUtil {
+
+  private static final ObjectReader READER =
+      new ObjectMapper().readerFor(Map.class);
+
   static FileStatus toFileStatus(HdfsFileStatus f, String parent) {
     return new FileStatus(f.getLen(), f.isDirectory(), f.getReplication(),
         f.getBlockSize(), f.getModificationTime(), f.getAccessTime(),
@@ -76,9 +80,8 @@ public class TestJsonUtil {
     System.out.println("fstatus = " + fstatus);
     final String json = JsonUtil.toJsonString(status, true);
     System.out.println("json    = " + json.replace(",", ",\n  "));
-    ObjectReader reader = new ObjectMapper().readerFor(Map.class);
     final HdfsFileStatus s2 =
-        JsonUtilClient.toFileStatus((Map<?, ?>) reader.readValue(json), true);
+        JsonUtilClient.toFileStatus((Map<?, ?>) READER.readValue(json), true);
     final FileStatus fs2 = toFileStatus(s2, parent);
     System.out.println("s2      = " + s2);
     System.out.println("fs2     = " + fs2);
@@ -164,8 +167,7 @@ public class TestJsonUtil {
   public void testToAclStatus() throws IOException {
     String jsonString =
         "{\"AclStatus\":{\"entries\":[\"user::rwx\",\"user:user1:rw-\",\"group::rw-\",\"other::r-x\"],\"group\":\"supergroup\",\"owner\":\"testuser\",\"stickyBit\":false}}";
-    ObjectReader reader = new ObjectMapper().readerFor(Map.class);
-    Map<?, ?> json = reader.readValue(jsonString);
+    Map<?, ?> json = READER.readValue(jsonString);
 
     List<AclEntry> aclSpec =
         Lists.newArrayList(aclEntry(ACCESS, USER, ALL),
@@ -224,8 +226,7 @@ public class TestJsonUtil {
     String jsonString = 
         "{\"XAttrs\":[{\"name\":\"user.a1\",\"value\":\"0x313233\"}," +
         "{\"name\":\"user.a2\",\"value\":\"0x313131\"}]}";
-    ObjectReader reader = new ObjectMapper().readerFor(Map.class);
-    Map<?, ?> json = reader.readValue(jsonString);
+    Map<?, ?> json = READER.readValue(jsonString);
     XAttr xAttr1 = (new XAttr.Builder()).setNameSpace(XAttr.NameSpace.USER).
         setName("a1").setValue(XAttrCodec.decodeValue("0x313233")).build();
     XAttr xAttr2 = (new XAttr.Builder()).setNameSpace(XAttr.NameSpace.USER).
@@ -250,8 +251,7 @@ public class TestJsonUtil {
     String jsonString = 
         "{\"XAttrs\":[{\"name\":\"user.a1\",\"value\":\"0x313233\"}," +
         "{\"name\":\"user.a2\",\"value\":\"0x313131\"}]}";
-    ObjectReader reader = new ObjectMapper().readerFor(Map.class);
-    Map<?, ?> json = reader.readValue(jsonString);
+    Map<?, ?> json = READER.readValue(jsonString);
 
     // Get xattr: user.a2
     byte[] value = JsonUtilClient.getXAttr(json, "user.a2");