HDFS-12269. Better to return a Map rather than HashMap in getErasureCodingCodecs. Contributed by Huafeng Wang.

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/erasurecode/CodecRegistry.java

@@ -176,7 +176,7 @@ public final class CodecRegistry {
    * @return a map of all codec names, and their corresponding code list
    * separated by ','.
    */
-  public HashMap<String, String> getCodec2CoderCompactMap() {
+  public Map<String, String> getCodec2CoderCompactMap() {
     return coderNameCompactMap;
   }
 }

hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/DFSClient.java

@@ -2764,7 +2764,7 @@ public class DFSClient implements java.io.Closeable, RemotePeerFactory,
     }
   }
 
-  public HashMap<String, String> getErasureCodingCodecs() throws IOException {
+  public Map<String, String> getErasureCodingCodecs() throws IOException {
     checkOpen();
     try (TraceScope ignored = tracer.newScope("getErasureCodingCodecs")) {
       return namenode.getErasureCodingCodecs();

hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/DistributedFileSystem.java

@@ -26,7 +26,6 @@ import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collection;
 import java.util.EnumSet;
-import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 
@@ -2585,7 +2584,7 @@ public class DistributedFileSystem extends FileSystem {
    * @return all erasure coding codecs and coders supported by this file system.
    * @throws IOException
    */
-  public HashMap<String, String> getAllErasureCodingCodecs()
+  public Map<String, String> getAllErasureCodingCodecs()
       throws IOException {
     return dfs.getErasureCodingCodecs();
   }

hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/protocol/ClientProtocol.java

@@ -19,8 +19,8 @@ package org.apache.hadoop.hdfs.protocol;
 
 import java.io.IOException;
 import java.util.EnumSet;
-import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 import org.apache.hadoop.classification.InterfaceAudience;
 import org.apache.hadoop.classification.InterfaceStability;
@@ -1601,7 +1601,7 @@ public interface ClientProtocol {
    * @throws IOException
    */
   @Idempotent
-  HashMap<String, String> getErasureCodingCodecs() throws IOException;
+  Map<String, String> getErasureCodingCodecs() throws IOException;
 
   /**
    * Get the information about the EC policy for the path.

hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/protocolPB/ClientNamenodeProtocolTranslatorPB.java

@@ -26,6 +26,7 @@ import java.util.List;
 
 import com.google.common.collect.Lists;
 
+import java.util.Map;
 import java.util.concurrent.TimeUnit;
 import java.util.stream.Collectors;
 
@@ -1760,11 +1761,11 @@ public class ClientNamenodeProtocolTranslatorPB implements
   }
 
   @Override
-  public HashMap<String, String> getErasureCodingCodecs() throws IOException {
+  public Map<String, String> getErasureCodingCodecs() throws IOException {
     try {
       GetErasureCodingCodecsResponseProto response = rpcProxy
           .getErasureCodingCodecs(null, VOID_GET_EC_CODEC_REQUEST);
-      HashMap<String, String> ecCodecs = new HashMap<String, String>();
+      Map<String, String> ecCodecs = new HashMap<>();
       for (CodecProto codec : response.getCodecList()) {
         ecCodecs.put(codec.getCodec(), codec.getCoders());
       }

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/protocolPB/ClientNamenodeProtocolServerSideTranslatorPB.java

@@ -21,7 +21,6 @@ import java.io.IOException;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.EnumSet;
-import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.stream.Collectors;
@@ -1664,7 +1663,7 @@ public class ClientNamenodeProtocolServerSideTranslatorPB implements
       RpcController controller, GetErasureCodingCodecsRequestProto request)
       throws ServiceException {
     try {
-      HashMap<String, String> codecs = server.getErasureCodingCodecs();
+      Map<String, String> codecs = server.getErasureCodingCodecs();
       GetErasureCodingCodecsResponseProto.Builder resBuilder =
           GetErasureCodingCodecsResponseProto.newBuilder();
       for (Map.Entry<String, String> codec : codecs.entrySet()) {

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSDirErasureCodingOp.java

@@ -25,8 +25,8 @@ import java.io.FileNotFoundException;
 import java.io.IOException;
 import java.util.Arrays;
 import java.util.EnumSet;
-import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 import java.util.stream.Collectors;
 
 import com.google.common.base.Preconditions;
@@ -344,7 +344,7 @@ final class FSDirErasureCodingOp {
    * @param fsn namespace
    * @return {@link java.util.HashMap} array
    */
-  static HashMap<String, String> getErasureCodingCodecs(final FSNamesystem fsn)
+  static Map<String, String> getErasureCodingCodecs(final FSNamesystem fsn)
       throws IOException {
     assert fsn.hasReadLock();
     return CodecRegistry.getInstance().getCodec2CoderCompactMap();

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSNamesystem.java

@@ -7255,14 +7255,14 @@ public class FSNamesystem implements Namesystem, FSNamesystemMBean,
   /**
    * Get available erasure coding codecs and corresponding coders.
    */
-  HashMap<String, String> getErasureCodingCodecs() throws IOException {
+  Map<String, String> getErasureCodingCodecs() throws IOException {
     final String operationName = "getErasureCodingCodecs";
     boolean success = false;
     checkOperation(OperationCategory.READ);
     readLock();
     try {
       checkOperation(OperationCategory.READ);
-      final HashMap<String, String> ret =
+      final Map<String, String> ret =
           FSDirErasureCodingOp.getErasureCodingCodecs(this);
       success = true;
       return ret;

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/NameNodeRpcServer.java

@@ -37,9 +37,9 @@ import java.net.InetSocketAddress;
 import java.util.Arrays;
 import java.util.Collection;
 import java.util.EnumSet;
-import java.util.HashMap;
 import java.util.HashSet;
 import java.util.List;
+import java.util.Map;
 import java.util.Set;
 import java.util.concurrent.Callable;
 
@@ -2278,7 +2278,7 @@ public class NameNodeRpcServer implements NamenodeProtocols {
   }
 
   @Override // ClientProtocol
-  public HashMap<String, String> getErasureCodingCodecs() throws IOException {
+  public Map<String, String> getErasureCodingCodecs() throws IOException {
     checkNNStartup();
     return namesystem.getErasureCodingCodecs();
   }

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/tools/ECAdmin.java

@@ -33,7 +33,6 @@ import org.apache.hadoop.util.ToolRunner;
 import java.io.IOException;
 import java.util.Arrays;
 import java.util.Collection;
-import java.util.HashMap;
 import java.util.LinkedList;
 import java.util.List;
 import java.util.Map;
@@ -441,7 +440,7 @@ public class ECAdmin extends Configured implements Tool {
 
       final DistributedFileSystem dfs = AdminHelper.getDFS(conf);
       try {
-        HashMap<String, String> codecs =
+        Map<String, String> codecs =
             dfs.getAllErasureCodingCodecs();
         if (codecs.isEmpty()) {
           System.out.println("No erasure coding codecs are supported on the " +

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/TestErasureCodingPolicies.java

@@ -50,8 +50,8 @@ import java.io.IOException;
 import java.security.PrivilegedExceptionAction;
 import java.util.Collection;
 import java.util.EnumSet;
-import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 import static org.apache.hadoop.test.GenericTestUtils.assertExceptionContains;
 import static org.junit.Assert.*;
@@ -647,7 +647,7 @@ public class TestErasureCodingPolicies {
 
   @Test
   public void testGetAllErasureCodingCodecs() throws Exception {
-    HashMap<String, String> allECCodecs = fs
+    Map<String, String> allECCodecs = fs
         .getAllErasureCodingCodecs();
     assertTrue("At least 3 system codecs should be enabled",
         allECCodecs.size() >= 3);