HADOOP-15835. Reuse Object Mapper in KMSJSONWriter (jeagles)

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

@@ -19,7 +19,7 @@ package org.apache.hadoop.crypto.key.kms.server;
 
 import org.apache.hadoop.classification.InterfaceAudience;
 import org.codehaus.jackson.map.ObjectMapper;
-
+import org.codehaus.jackson.map.ObjectWriter;
 import javax.ws.rs.Produces;
 import javax.ws.rs.WebApplicationException;
 import javax.ws.rs.core.MediaType;
@@ -44,6 +44,8 @@ import java.util.Map;
 @Produces(MediaType.APPLICATION_JSON)
 @InterfaceAudience.Private
 public class KMSJSONWriter implements MessageBodyWriter<Object> {
+  private static final ObjectWriter WRITER =
+      new ObjectMapper().writerWithDefaultPrettyPrinter();
 
   @Override
   public boolean isWriteable(Class<?> aClass, Type type,
@@ -65,8 +67,7 @@ public class KMSJSONWriter implements MessageBodyWriter<Object> {
       OutputStream outputStream) throws IOException, WebApplicationException {
     Writer writer = new OutputStreamWriter(outputStream, Charset
         .forName("UTF-8"));
-    ObjectMapper jsonMapper = new ObjectMapper();
-    jsonMapper.writerWithDefaultPrettyPrinter().writeValue(writer, obj);
+    WRITER.writeValue(writer, obj);
   }
 
 }