Merge pull request #204 from pherl/master

Implement maps for JavaNano

15 files changed, 1163 insertions, 87 deletions

diff --git a/javanano/pom.xml b/javanano/pom.xml
index 3d98a5e0..409d8d61 100644
--- a/javanano/pom.xml
+++ b/javanano/pom.xml
@@ -94,6 +94,7 @@
                   <arg value="src/test/java/com/google/protobuf/nano/unittest_multiple_nameclash_nano.proto" />
                   <arg value="src/test/java/com/google/protobuf/nano/unittest_enum_class_nano.proto" />
                   <arg value="src/test/java/com/google/protobuf/nano/unittest_repeated_merge_nano.proto" />
+                  <arg value="src/test/java/com/google/protobuf/nano/map_test.proto" />
                 </exec>
                 <exec executable="../src/protoc">
                   <arg value="--javanano_out=store_unknown_fields=true,generate_equals=true:target/generated-test-sources" />
diff --git a/javanano/src/main/java/com/google/protobuf/nano/CodedInputByteBufferNano.java b/javanano/src/main/java/com/google/protobuf/nano/CodedInputByteBufferNano.java
index b147f69d..b4f20fde 100644
--- a/javanano/src/main/java/com/google/protobuf/nano/CodedInputByteBufferNano.java
+++ b/javanano/src/main/java/com/google/protobuf/nano/CodedInputByteBufferNano.java
@@ -638,4 +638,44 @@ public final class CodedInputByteBufferNano {
       throw InvalidProtocolBufferNanoException.truncatedMessage();
     }
   }
+
+  // Read a primitive type.
+  Object readPrimitiveField(int type) throws IOException {
+    switch (type) {
+      case InternalNano.TYPE_DOUBLE:
+          return readDouble();
+      case InternalNano.TYPE_FLOAT:
+          return readFloat();
+      case InternalNano.TYPE_INT64:
+          return readInt64();
+      case InternalNano.TYPE_UINT64:
+          return readUInt64();
+      case InternalNano.TYPE_INT32:
+          return readInt32();
+      case InternalNano.TYPE_FIXED64:
+          return readFixed64();
+      case InternalNano.TYPE_FIXED32:
+          return readFixed32();
+      case InternalNano.TYPE_BOOL:
+          return readBool();
+      case InternalNano.TYPE_STRING:
+          return readString();
+      case InternalNano.TYPE_BYTES:
+          return readBytes();
+      case InternalNano.TYPE_UINT32:
+          return readUInt32();
+      case InternalNano.TYPE_ENUM:
+          return readEnum();
+      case InternalNano.TYPE_SFIXED32:
+          return readSFixed32();
+      case InternalNano.TYPE_SFIXED64:
+          return readSFixed64();
+      case InternalNano.TYPE_SINT32:
+          return readSInt32();
+      case InternalNano.TYPE_SINT64:
+          return readSInt64();
+      default:
+          throw new IllegalArgumentException("Unknown type " + type);
+    }
+  }
 }
diff --git a/javanano/src/main/java/com/google/protobuf/nano/CodedOutputByteBufferNano.java b/javanano/src/main/java/com/google/protobuf/nano/CodedOutputByteBufferNano.java
index 37982b57..2777f34c 100644
--- a/javanano/src/main/java/com/google/protobuf/nano/CodedOutputByteBufferNano.java
+++ b/javanano/src/main/java/com/google/protobuf/nano/CodedOutputByteBufferNano.java
@@ -876,4 +876,128 @@ public final class CodedOutputByteBufferNano {
     // Note:  the right-shift must be arithmetic
     return (n << 1) ^ (n >> 63);
   }
+
+  static int computeFieldSize(int number, int type, Object object) {
+    switch (type) {
+      case InternalNano.TYPE_BOOL:
+        return computeBoolSize(number, (Boolean) object);
+      case InternalNano.TYPE_BYTES:
+        return computeBytesSize(number, (byte[]) object);
+      case InternalNano.TYPE_STRING:
+        return computeStringSize(number, (String) object);
+      case InternalNano.TYPE_FLOAT:
+        return computeFloatSize(number, (Float) object);
+      case InternalNano.TYPE_DOUBLE:
+        return computeDoubleSize(number, (Double) object);
+      case InternalNano.TYPE_ENUM:
+        return computeEnumSize(number, (Integer) object);
+      case InternalNano.TYPE_FIXED32:
+        return computeFixed32Size(number, (Integer) object);
+      case InternalNano.TYPE_INT32:
+        return computeInt32Size(number, (Integer) object);
+      case InternalNano.TYPE_UINT32:
+        return computeUInt32Size(number, (Integer) object);
+      case InternalNano.TYPE_SINT32:
+        return computeSInt32Size(number, (Integer) object);
+      case InternalNano.TYPE_SFIXED32:
+        return computeSFixed32Size(number, (Integer) object);
+      case InternalNano.TYPE_INT64:
+        return computeInt64Size(number, (Long) object);
+      case InternalNano.TYPE_UINT64:
+        return computeUInt64Size(number, (Long) object);
+      case InternalNano.TYPE_SINT64:
+        return computeSInt64Size(number, (Long) object);
+      case InternalNano.TYPE_FIXED64:
+        return computeFixed64Size(number, (Long) object);
+      case InternalNano.TYPE_SFIXED64:
+        return computeSFixed64Size(number, (Long) object);
+      case InternalNano.TYPE_MESSAGE:
+        return computeMessageSize(number, (MessageNano) object);
+      case InternalNano.TYPE_GROUP:
+        return computeGroupSize(number, (MessageNano) object);
+      default:
+        throw new IllegalArgumentException("Unknown type: " + type);
+    }
+  }
+
+  void writeField(int number, int type, Object value)
+      throws IOException {
+    switch (type) {
+      case InternalNano.TYPE_DOUBLE:
+        Double doubleValue = (Double) value;
+        writeDouble(number, doubleValue);
+        break;
+      case InternalNano.TYPE_FLOAT:
+        Float floatValue = (Float) value;
+        writeFloat(number, floatValue);
+        break;
+      case InternalNano.TYPE_INT64:
+        Long int64Value = (Long) value;
+        writeInt64(number, int64Value);
+        break;
+      case InternalNano.TYPE_UINT64:
+        Long uint64Value = (Long) value;
+        writeUInt64(number, uint64Value);
+        break;
+      case InternalNano.TYPE_INT32:
+        Integer int32Value = (Integer) value;
+        writeInt32(number, int32Value);
+        break;
+      case InternalNano.TYPE_FIXED64:
+        Long fixed64Value = (Long) value;
+        writeFixed64(number, fixed64Value);
+        break;
+      case InternalNano.TYPE_FIXED32:
+        Integer fixed32Value = (Integer) value;
+        writeFixed32(number, fixed32Value);
+        break;
+      case InternalNano.TYPE_BOOL:
+        Boolean boolValue = (Boolean) value;
+        writeBool(number, boolValue);
+        break;
+      case InternalNano.TYPE_STRING:
+        String stringValue = (String) value;
+        writeString(number, stringValue);
+        break;
+      case InternalNano.TYPE_BYTES:
+        byte[] bytesValue = (byte[]) value;
+        writeBytes(number, bytesValue);
+        break;
+      case InternalNano.TYPE_UINT32:
+        Integer uint32Value = (Integer) value;
+        writeUInt32(number, uint32Value);
+        break;
+      case InternalNano.TYPE_ENUM:
+        Integer enumValue = (Integer) value;
+        writeEnum(number, enumValue);
+        break;
+      case InternalNano.TYPE_SFIXED32:
+        Integer sfixed32Value = (Integer) value;
+        writeSFixed32(number, sfixed32Value);
+        break;
+      case InternalNano.TYPE_SFIXED64:
+        Long sfixed64Value = (Long) value;
+        writeSFixed64(number, sfixed64Value);
+        break;
+      case InternalNano.TYPE_SINT32:
+        Integer sint32Value = (Integer) value;
+        writeSInt32(number, sint32Value);
+        break;
+      case InternalNano.TYPE_SINT64:
+        Long sint64Value = (Long) value;
+        writeSInt64(number, sint64Value);
+        break;
+      case InternalNano.TYPE_MESSAGE:
+        MessageNano messageValue = (MessageNano) value;
+        writeMessage(number, messageValue);
+        break;
+      case InternalNano.TYPE_GROUP:
+        MessageNano groupValue = (MessageNano) value;
+        writeGroup(number, groupValue);
+        break;
+      default:
+        throw new IOException("Unknown type: " + type);
+    }
+  }
+
 }
diff --git a/javanano/src/main/java/com/google/protobuf/nano/Extension.java b/javanano/src/main/java/com/google/protobuf/nano/Extension.java
index 5d18ae6e..c29b030f 100644
--- a/javanano/src/main/java/com/google/protobuf/nano/Extension.java
+++ b/javanano/src/main/java/com/google/protobuf/nano/Extension.java
@@ -55,24 +55,24 @@ public class Extension<M extends ExtendableMessageNano<M>, T> {
      *       PrimitiveExtension      // for primitive/enum typed extensions
      */
 
-    public static final int TYPE_DOUBLE   = 1;
-    public static final int TYPE_FLOAT    = 2;
-    public static final int TYPE_INT64    = 3;
-    public static final int TYPE_UINT64   = 4;
-    public static final int TYPE_INT32    = 5;
-    public static final int TYPE_FIXED64  = 6;
-    public static final int TYPE_FIXED32  = 7;
-    public static final int TYPE_BOOL     = 8;
-    public static final int TYPE_STRING   = 9;
-    public static final int TYPE_GROUP    = 10;
-    public static final int TYPE_MESSAGE  = 11;
-    public static final int TYPE_BYTES    = 12;
-    public static final int TYPE_UINT32   = 13;
-    public static final int TYPE_ENUM     = 14;
-    public static final int TYPE_SFIXED32 = 15;
-    public static final int TYPE_SFIXED64 = 16;
-    public static final int TYPE_SINT32   = 17;
-    public static final int TYPE_SINT64   = 18;
+    public static final int TYPE_DOUBLE   = InternalNano.TYPE_DOUBLE;
+    public static final int TYPE_FLOAT    = InternalNano.TYPE_FLOAT;
+    public static final int TYPE_INT64    = InternalNano.TYPE_INT64;
+    public static final int TYPE_UINT64   = InternalNano.TYPE_UINT64;
+    public static final int TYPE_INT32    = InternalNano.TYPE_INT32;
+    public static final int TYPE_FIXED64  = InternalNano.TYPE_FIXED64;
+    public static final int TYPE_FIXED32  = InternalNano.TYPE_FIXED32;
+    public static final int TYPE_BOOL     = InternalNano.TYPE_BOOL;
+    public static final int TYPE_STRING   = InternalNano.TYPE_STRING;
+    public static final int TYPE_GROUP    = InternalNano.TYPE_GROUP;
+    public static final int TYPE_MESSAGE  = InternalNano.TYPE_MESSAGE;
+    public static final int TYPE_BYTES    = InternalNano.TYPE_BYTES;
+    public static final int TYPE_UINT32   = InternalNano.TYPE_UINT32;
+    public static final int TYPE_ENUM     = InternalNano.TYPE_ENUM;
+    public static final int TYPE_SFIXED32 = InternalNano.TYPE_SFIXED32;
+    public static final int TYPE_SFIXED64 = InternalNano.TYPE_SFIXED64;
+    public static final int TYPE_SINT32   = InternalNano.TYPE_SINT32;
+    public static final int TYPE_SINT64   = InternalNano.TYPE_SINT64;
 
     /**
      * Creates an {@code Extension} of the given message type and tag number.
@@ -338,42 +338,7 @@ public class Extension<M extends ExtendableMessageNano<M>, T> {
         @Override
         protected Object readData(CodedInputByteBufferNano input) {
             try {
-                switch (type) {
-                    case TYPE_DOUBLE:
-                        return input.readDouble();
-                    case TYPE_FLOAT:
-                        return input.readFloat();
-                    case TYPE_INT64:
-                        return input.readInt64();
-                    case TYPE_UINT64:
-                        return input.readUInt64();
-                    case TYPE_INT32:
-                        return input.readInt32();
-                    case TYPE_FIXED64:
-                        return input.readFixed64();
-                    case TYPE_FIXED32:
-                        return input.readFixed32();
-                    case TYPE_BOOL:
-                        return input.readBool();
-                    case TYPE_STRING:
-                        return input.readString();
-                    case TYPE_BYTES:
-                        return input.readBytes();
-                    case TYPE_UINT32:
-                        return input.readUInt32();
-                    case TYPE_ENUM:
-                        return input.readEnum();
-                    case TYPE_SFIXED32:
-                        return input.readSFixed32();
-                    case TYPE_SFIXED64:
-                        return input.readSFixed64();
-                    case TYPE_SINT32:
-                        return input.readSInt32();
-                    case TYPE_SINT64:
-                        return input.readSInt64();
-                    default:
-                        throw new IllegalArgumentException("Unknown type " + type);
-                }
+              return input.readPrimitiveField(type);
             } catch (IOException e) {
                 throw new IllegalArgumentException("Error reading extension field", e);
             }
diff --git a/javanano/src/main/java/com/google/protobuf/nano/InternalNano.java b/javanano/src/main/java/com/google/protobuf/nano/InternalNano.java
index e08bb4b7..c92ec417 100644
--- a/javanano/src/main/java/com/google/protobuf/nano/InternalNano.java
+++ b/javanano/src/main/java/com/google/protobuf/nano/InternalNano.java
@@ -30,8 +30,13 @@
 
 package com.google.protobuf.nano;
 
+import com.google.protobuf.nano.MapFactories.MapFactory;
+
+import java.io.IOException;
 import java.io.UnsupportedEncodingException;
 import java.util.Arrays;
+import java.util.Map;
+import java.util.Map.Entry;
 
 /**
  * The classes contained within are used internally by the Protocol Buffer
@@ -43,6 +48,26 @@ import java.util.Arrays;
  */
 public final class InternalNano {
 
+  public static final int TYPE_DOUBLE   = 1;
+  public static final int TYPE_FLOAT    = 2;
+  public static final int TYPE_INT64    = 3;
+  public static final int TYPE_UINT64   = 4;
+  public static final int TYPE_INT32    = 5;
+  public static final int TYPE_FIXED64  = 6;
+  public static final int TYPE_FIXED32  = 7;
+  public static final int TYPE_BOOL     = 8;
+  public static final int TYPE_STRING   = 9;
+  public static final int TYPE_GROUP    = 10;
+  public static final int TYPE_MESSAGE  = 11;
+  public static final int TYPE_BYTES    = 12;
+  public static final int TYPE_UINT32   = 13;
+  public static final int TYPE_ENUM     = 14;
+  public static final int TYPE_SFIXED32 = 15;
+  public static final int TYPE_SFIXED64 = 16;
+  public static final int TYPE_SINT32   = 17;
+  public static final int TYPE_SINT64   = 18;
+
+
   private InternalNano() {}
 
   /**
@@ -329,5 +354,203 @@ public final class InternalNano {
     }
     return result;
   }
+  private static final byte[] EMPTY_BYTES = new byte[0];
+  private static Object primitiveDefaultValue(int type) {
+    switch (type) {
+      case TYPE_BOOL:
+        return Boolean.FALSE;
+      case TYPE_BYTES:
+        return EMPTY_BYTES;
+      case TYPE_STRING:
+        return "";
+      case TYPE_FLOAT:
+        return Float.valueOf(0);
+      case TYPE_DOUBLE:
+        return Double.valueOf(0);
+      case TYPE_ENUM:
+      case TYPE_FIXED32:
+      case TYPE_INT32:
+      case TYPE_UINT32:
+      case TYPE_SINT32:
+      case TYPE_SFIXED32:
+        return Integer.valueOf(0);
+      case TYPE_INT64:
+      case TYPE_UINT64:
+      case TYPE_SINT64:
+      case TYPE_FIXED64:
+      case TYPE_SFIXED64:
+        return Long.valueOf(0L);
+      case TYPE_MESSAGE:
+      case TYPE_GROUP:
+      default:
+        throw new IllegalArgumentException(
+            "Type: " + type + " is not a primitive type.");
+    }
+  }
+
+  /**
+   * Merges the map entry into the map field. Note this is only supposed to
+   * be called by generated messages.
+   *
+   * @param map the map field; may be null, in which case a map will be
+   *        instantiated using the {@link MapFactories.MapFactory}
+   * @param input the input byte buffer
+   * @param keyType key type, as defined in InternalNano.TYPE_*
+   * @param valueType value type, as defined in InternalNano.TYPE_*
+   * @param value an new instance of the value, if the value is a TYPE_MESSAGE;
+   *        otherwise this parameter can be null and will be ignored.
+   * @param keyTag wire tag for the key
+   * @param valueTag wire tag for the value
+   * @return the map field
+   * @throws IOException
+   */
+  @SuppressWarnings("unchecked")
+  public static final <K, V> Map<K, V> mergeMapEntry(
+      CodedInputByteBufferNano input,
+      Map<K, V> map,
+      MapFactory mapFactory,
+      int keyType,
+      int valueType,
+      V value,
+      int keyTag,
+      int valueTag) throws IOException {
+    map = mapFactory.forMap(map);
+    final int length = input.readRawVarint32();
+    final int oldLimit = input.pushLimit(length);
+    K key = null;
+    while (true) {
+      int tag = input.readTag();
+      if (tag == 0) {
+        break;
+      }
+      if (tag == keyTag) {
+        key = (K) input.readPrimitiveField(keyType);
+      } else if (tag == valueTag) {
+        if (valueType == TYPE_MESSAGE) {
+          input.readMessage((MessageNano) value);
+        } else {
+          value = (V) input.readPrimitiveField(valueType);
+        }
+      } else {
+        if (!input.skipField(tag)) {
+          break;
+        }
+      }
+    }
+    input.checkLastTagWas(0);
+    input.popLimit(oldLimit);
+
+    if (key == null) {
+      // key can only be primitive types.
+      key = (K) primitiveDefaultValue(keyType);
+    }
+
+    if (value == null) {
+      // message type value will be initialized by code-gen.
+      value = (V) primitiveDefaultValue(valueType);
+    }
+
+    map.put(key, value);
+    return map;
+  }
+
+  public static <K, V> void serializeMapField(
+      CodedOutputByteBufferNano output,
+      Map<K, V> map, int number, int keyType, int valueType)
+          throws IOException {
+    for (Entry<K, V> entry: map.entrySet()) {
+      K key = entry.getKey();
+      V value = entry.getValue();
+      if (key == null || value == null) {
+        throw new IllegalStateException(
+            "keys and values in maps cannot be null");
+      }
+      int entrySize =
+          CodedOutputByteBufferNano.computeFieldSize(1, keyType, key) +
+          CodedOutputByteBufferNano.computeFieldSize(2, valueType, value);
+      output.writeTag(number, WireFormatNano.WIRETYPE_LENGTH_DELIMITED);
+      output.writeRawVarint32(entrySize);
+      output.writeField(1, keyType, key);
+      output.writeField(2, valueType, value);
+    }
+  }
+
+  public static <K, V> int computeMapFieldSize(
+      Map<K, V> map, int number, int keyType, int valueType) {
+    int size = 0;
+    int tagSize = CodedOutputByteBufferNano.computeTagSize(number);
+    for (Entry<K, V> entry: map.entrySet()) {
+      K key = entry.getKey();
+      V value = entry.getValue();
+      if (key == null || value == null) {
+        throw new IllegalStateException(
+            "keys and values in maps cannot be null");
+      }
+      int entrySize =
+          CodedOutputByteBufferNano.computeFieldSize(1, keyType, key) +
+          CodedOutputByteBufferNano.computeFieldSize(2, valueType, value);
+      size += tagSize + entrySize
+          + CodedOutputByteBufferNano.computeRawVarint32Size(entrySize);
+    }
+    return size;
+  }
+
+  /**
+   * Checks whether two {@link Map} are equal. We don't use the default equals
+   * method of {@link Map} because it compares by identity not by content for
+   * byte arrays.
+   */
+  public static <K, V> boolean equals(Map<K, V> a, Map<K, V> b) {
+    if (a == b) {
+      return true;
+    }
+    if (a == null) {
+      return b.size() == 0;
+    }
+    if (b == null) {
+      return a.size() == 0;
+    }
+    if (a.size() != b.size()) {
+      return false;
+    }
+    for (Entry<K, V> entry : a.entrySet()) {
+      if (!b.containsKey(entry.getKey())) {
+        return false;
+      }
+      if (!equalsMapValue(entry.getValue(), b.get(entry.getKey()))) {
+        return false;
+      }
+    }
+    return true;
+  }
+
+  private static boolean equalsMapValue(Object a, Object b) {
+    if (a == null || b == null) {
+      throw new IllegalStateException(
+          "keys and values in maps cannot be null");
+    }
+    if (a instanceof byte[] && b instanceof byte[]) {
+      return Arrays.equals((byte[]) a, (byte[]) b);
+    }
+    return a.equals(b);
+  }
+
+  public static <K, V> int hashCode(Map<K, V> map) {
+    if (map == null) {
+      return 0;
+    }
+    int result = 0;
+    for (Entry<K, V> entry : map.entrySet()) {
+      result += hashCodeForMap(entry.getKey())
+          ^ hashCodeForMap(entry.getValue());
+    }
+    return result;
+  }
 
+  private static int hashCodeForMap(Object o) {
+    if (o instanceof byte[]) {
+      return Arrays.hashCode((byte[]) o);
+    }
+    return o.hashCode();
+  }
 }
diff --git a/javanano/src/main/java/com/google/protobuf/nano/MapFactories.java b/javanano/src/main/java/com/google/protobuf/nano/MapFactories.java
new file mode 100644
index 00000000..98fa4877
--- /dev/null
+++ b/javanano/src/main/java/com/google/protobuf/nano/MapFactories.java
@@ -0,0 +1,67 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2013 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package com.google.protobuf.nano;
+
+import java.util.HashMap;
+import java.util.Map;
+
+/**
+ * Utility class for maps support.
+ */
+public final class MapFactories {
+  public static interface MapFactory {
+    <K, V> Map<K, V> forMap(Map<K, V> oldMap);
+  }
+
+  // NOTE(liujisi): The factory setter is temporarily marked as package private.
+  // The way to provide customized implementations of maps for different
+  // platforms are still under discussion.  Mark it as private to avoid exposing
+  // the API in proto3 alpha release.
+  /* public */ static void setMapFactory(MapFactory newMapFactory) {
+    mapFactory = newMapFactory;
+  }
+
+  public static MapFactory getMapFactory() {
+    return mapFactory;
+  }
+
+  private static class DefaultMapFactory implements MapFactory {
+    public <K, V> Map<K, V> forMap(Map<K, V> oldMap) {
+      if (oldMap == null) {
+        return new HashMap<K, V>();
+      }
+      return oldMap;
+    }
+  }
+  private static volatile MapFactory mapFactory = new DefaultMapFactory();
+
+  private MapFactories() {}
+}
diff --git a/javanano/src/test/java/com/google/protobuf/nano/NanoTest.java b/javanano/src/test/java/com/google/protobuf/nano/NanoTest.java
index 442f0b74..aa279da2 100644
--- a/javanano/src/test/java/com/google/protobuf/nano/NanoTest.java
+++ b/javanano/src/test/java/com/google/protobuf/nano/NanoTest.java
@@ -30,31 +30,11 @@
 
 package com.google.protobuf.nano;
 
-import com.google.protobuf.nano.CodedInputByteBufferNano;
-import com.google.protobuf.nano.EnumClassNanoMultiple;
-import com.google.protobuf.nano.EnumClassNanos;
-import com.google.protobuf.nano.EnumValidity;
-import com.google.protobuf.nano.EnumValidityAccessors;
-import com.google.protobuf.nano.FileScopeEnumMultiple;
-import com.google.protobuf.nano.FileScopeEnumRefNano;
-import com.google.protobuf.nano.InternalNano;
-import com.google.protobuf.nano.InvalidProtocolBufferNanoException;
-import com.google.protobuf.nano.MessageNano;
-import com.google.protobuf.nano.MessageScopeEnumRefNano;
-import com.google.protobuf.nano.MultipleImportingNonMultipleNano1;
-import com.google.protobuf.nano.MultipleImportingNonMultipleNano2;
-import com.google.protobuf.nano.MultipleNameClashNano;
+import com.google.protobuf.nano.MapTestProto.TestMap;
+import com.google.protobuf.nano.MapTestProto.TestMap.MessageValue;
 import com.google.protobuf.nano.NanoAccessorsOuterClass.TestNanoAccessors;
 import com.google.protobuf.nano.NanoHasOuterClass.TestAllTypesNanoHas;
-import com.google.protobuf.nano.NanoOuterClass;
 import com.google.protobuf.nano.NanoOuterClass.TestAllTypesNano;
-import com.google.protobuf.nano.NanoReferenceTypes;
-import com.google.protobuf.nano.NanoRepeatedPackables;
-import com.google.protobuf.nano.PackedExtensions;
-import com.google.protobuf.nano.RepeatedExtensions;
-import com.google.protobuf.nano.SingularExtensions;
-import com.google.protobuf.nano.TestRepeatedMergeNano;
-import com.google.protobuf.nano.UnittestMultipleNano;
 import com.google.protobuf.nano.UnittestRecursiveNano.RecursiveMessageNano;
 import com.google.protobuf.nano.UnittestSimpleNano.SimpleMessageNano;
 import com.google.protobuf.nano.UnittestSingleNano.SingleMessageNano;
@@ -67,6 +47,8 @@ import junit.framework.TestCase;
 
 import java.util.Arrays;
 import java.util.HashMap;
+import java.util.Map;
+import java.util.TreeMap;
 
 /**
  * Test nano runtime.
@@ -3754,6 +3736,320 @@ public class NanoTest extends TestCase {
     assertTrue(Arrays.equals(new boolean[] {false, true, false, true}, nonPacked.bools));
   }
 
+  public void testMapsSerializeAndParse() throws Exception {
+    TestMap origin = new TestMap();
+    setMapMessage(origin);
+    assertMapMessageSet(origin);
+
+    byte[] output = MessageNano.toByteArray(origin);
+    TestMap parsed = new TestMap();
+    MessageNano.mergeFrom(parsed, output);
+  }
+
+  public void testMapSerializeRejectNull() throws Exception {
+    TestMap primitiveMap = new TestMap();
+    primitiveMap.int32ToInt32Field = new HashMap<Integer, Integer>();
+    primitiveMap.int32ToInt32Field.put(null, 1);
+    try {
+      MessageNano.toByteArray(primitiveMap);
+      fail("should reject null keys");
+    } catch (IllegalStateException e) {
+      // pass.
+    }
+
+    TestMap messageMap = new TestMap();
+    messageMap.int32ToMessageField =
+        new HashMap<Integer, MapTestProto.TestMap.MessageValue>();
+    messageMap.int32ToMessageField.put(0, null);
+    try {
+      MessageNano.toByteArray(messageMap);
+      fail("should reject null values");
+    } catch (IllegalStateException e) {
+      // pass.
+    }
+  }
+
+  /**
+   * Tests that merging bytes containing conflicting keys with override the
+   * message value instead of merging the message value into the existing entry.
+   */
+  public void testMapMergeOverrideMessageValues() throws Exception {
+    TestMap.MessageValue origValue = new TestMap.MessageValue();
+    origValue.value = 1;
+    origValue.value2 = 2;
+    TestMap.MessageValue newValue = new TestMap.MessageValue();
+    newValue.value = 3;
+
+    TestMap origMessage = new TestMap();
+    origMessage.int32ToMessageField =
+        new HashMap<Integer, MapTestProto.TestMap.MessageValue>();
+    origMessage.int32ToMessageField.put(1, origValue);
+
+    TestMap newMessage = new TestMap();
+    newMessage.int32ToMessageField =
+        new HashMap<Integer, MapTestProto.TestMap.MessageValue>();
+    newMessage.int32ToMessageField.put(1, newValue);
+    MessageNano.mergeFrom(origMessage,
+        MessageNano.toByteArray(newMessage));
+    TestMap.MessageValue mergedValue = origMessage.int32ToMessageField.get(1);
+    assertEquals(3, mergedValue.value);
+    assertEquals(0, mergedValue.value2);
+  }
+
+  /**
+   * Tests that when merging with empty entries,
+   * we will use default for the key and value, instead of null.
+   */
+  public void testMapMergeEmptyEntry() throws Exception {
+    TestMap testMap = new TestMap();
+    byte[] buffer = new byte[1024];
+    CodedOutputByteBufferNano output =
+        CodedOutputByteBufferNano.newInstance(buffer);
+    // An empty entry for int32_to_int32 map.
+    output.writeTag(1, WireFormatNano.WIRETYPE_LENGTH_DELIMITED);
+    output.writeRawVarint32(0);
+    // An empty entry for int32_to_message map.
+    output.writeTag(5, WireFormatNano.WIRETYPE_LENGTH_DELIMITED);
+    output.writeRawVarint32(0);
+
+    CodedInputByteBufferNano input = CodedInputByteBufferNano.newInstance(
+        buffer, 0, buffer.length - output.spaceLeft());
+    testMap.mergeFrom(input);
+    assertNotNull(testMap.int32ToInt32Field);;
+    assertEquals(1, testMap.int32ToInt32Field.size());
+    assertEquals(Integer.valueOf(0), testMap.int32ToInt32Field.get(0));
+    assertNotNull(testMap.int32ToMessageField);
+    assertEquals(1, testMap.int32ToMessageField.size());
+    TestMap.MessageValue messageValue = testMap.int32ToMessageField.get(0);
+    assertNotNull(messageValue);
+    assertEquals(0, messageValue.value);
+    assertEquals(0, messageValue.value2);
+  }
+
+  public void testMapEquals() throws Exception {
+    TestMap a = new TestMap();
+    TestMap b = new TestMap();
+
+    // empty and null map fields are equal.
+    assertTestMapEqual(a, b);
+    a.int32ToBytesField = new HashMap<Integer, byte[]>();
+    assertTestMapEqual(a, b);
+
+    a.int32ToInt32Field = new HashMap<Integer, Integer>();
+    b.int32ToInt32Field = new HashMap<Integer, Integer>();
+    setMap(a.int32ToInt32Field, deepCopy(int32Values), deepCopy(int32Values));
+    setMap(b.int32ToInt32Field, deepCopy(int32Values), deepCopy(int32Values));
+    assertTestMapEqual(a, b);
+
+    a.int32ToMessageField =
+        new HashMap<Integer, MapTestProto.TestMap.MessageValue>();
+    b.int32ToMessageField =
+        new HashMap<Integer, MapTestProto.TestMap.MessageValue>();
+    setMap(a.int32ToMessageField,
+        deepCopy(int32Values), deepCopy(messageValues));
+    setMap(b.int32ToMessageField,
+        deepCopy(int32Values), deepCopy(messageValues));
+    assertTestMapEqual(a, b);
+
+    a.stringToInt32Field = new HashMap<String, Integer>();
+    b.stringToInt32Field = new HashMap<String, Integer>();
+    setMap(a.stringToInt32Field, deepCopy(stringValues), deepCopy(int32Values));
+    setMap(b.stringToInt32Field, deepCopy(stringValues), deepCopy(int32Values));
+    assertTestMapEqual(a, b);
+
+    a.int32ToBytesField = new HashMap<Integer, byte[]>();
+    b.int32ToBytesField = new HashMap<Integer, byte[]>();
+    setMap(a.int32ToBytesField, deepCopy(int32Values), deepCopy(bytesValues));
+    setMap(b.int32ToBytesField, deepCopy(int32Values), deepCopy(bytesValues));
+    assertTestMapEqual(a, b);
+
+    // Make sure the map implementation does not matter.
+    a.int32ToStringField = new TreeMap<Integer, String>();
+    b.int32ToStringField = new HashMap<Integer, String>();
+    setMap(a.int32ToStringField, deepCopy(int32Values), deepCopy(stringValues));
+    setMap(b.int32ToStringField, deepCopy(int32Values), deepCopy(stringValues));
+    assertTestMapEqual(a, b);
+
+    a.clear();
+    b.clear();
+
+    // unequal cases: different value
+    a.int32ToInt32Field = new HashMap<Integer, Integer>();
+    b.int32ToInt32Field = new HashMap<Integer, Integer>();
+    a.int32ToInt32Field.put(1, 1);
+    b.int32ToInt32Field.put(1, 2);
+    assertTestMapUnequal(a, b);
+    // unequal case: additional entry
+    b.int32ToInt32Field.put(1, 1);
+    b.int32ToInt32Field.put(2, 1);
+    assertTestMapUnequal(a, b);
+    a.int32ToInt32Field.put(2, 1);
+    assertTestMapEqual(a, b);
+
+    // unequal case: different message value.
+    a.int32ToMessageField =
+        new HashMap<Integer, MapTestProto.TestMap.MessageValue>();
+    b.int32ToMessageField =
+        new HashMap<Integer, MapTestProto.TestMap.MessageValue>();
+    MessageValue va = new MessageValue();
+    va.value = 1;
+    MessageValue vb = new MessageValue();
+    vb.value = 1;
+    a.int32ToMessageField.put(1, va);
+    b.int32ToMessageField.put(1, vb);
+    assertTestMapEqual(a, b);
+    vb.value = 2;
+    assertTestMapUnequal(a, b);
+  }
+
+  private static void assertTestMapEqual(TestMap a, TestMap b)
+      throws Exception {
+    assertEquals(a.hashCode(), b.hashCode());
+    assertTrue(a.equals(b));
+    assertTrue(b.equals(a));
+  }
+
+  private static void assertTestMapUnequal(TestMap a, TestMap b)
+      throws Exception {
+    assertFalse(a.equals(b));
+    assertFalse(b.equals(a));
+  }
+
+  private static final Integer[] int32Values = new Integer[] {
+    0, 1, -1, Integer.MAX_VALUE, Integer.MIN_VALUE,
+  };
+
+  private static final Long[] int64Values = new Long[] {
+    0L, 1L, -1L, Long.MAX_VALUE, Long.MIN_VALUE,
+  };
+
+  private static final String[] stringValues = new String[] {
+    "", "hello", "world", "foo", "bar",
+  };
+
+  private static final byte[][] bytesValues = new byte[][] {
+    new byte[] {},
+    new byte[] {0},
+    new byte[] {1, -1},
+    new byte[] {127, -128},
+    new byte[] {'a', 'b', '0', '1'},
+  };
+
+  private static final Boolean[] boolValues = new Boolean[] {
+    false, true,
+  };
+
+  private static final Integer[] enumValues = new Integer[] {
+    TestMap.FOO, TestMap.BAR, TestMap.BAZ, TestMap.QUX,
+    Integer.MAX_VALUE /* unknown */,
+  };
+
+  private static final TestMap.MessageValue[] messageValues =
+      new TestMap.MessageValue[] {
+    newMapValueMessage(0),
+    newMapValueMessage(1),
+    newMapValueMessage(-1),
+    newMapValueMessage(Integer.MAX_VALUE),
+    newMapValueMessage(Integer.MIN_VALUE),
+  };
+
+  private static TestMap.MessageValue newMapValueMessage(int value) {
+    TestMap.MessageValue result = new TestMap.MessageValue();
+    result.value = value;
+    return result;
+  }
+
+  @SuppressWarnings("unchecked")
+  private static <T> T[] deepCopy(T[] orig) throws Exception {
+    if (orig instanceof MessageValue[]) {
+      MessageValue[] result = new MessageValue[orig.length];
+      for (int i = 0; i < orig.length; i++) {
+        result[i] = new MessageValue();
+        MessageNano.mergeFrom(
+            result[i], MessageNano.toByteArray((MessageValue) orig[i]));
+      }
+      return (T[]) result;
+    }
+    if (orig instanceof byte[][]) {
+      byte[][] result = new byte[orig.length][];
+      for (int i = 0; i < orig.length; i++) {
+        byte[] origBytes = (byte[]) orig[i];
+        result[i] = Arrays.copyOf(origBytes, origBytes.length);
+      }
+    }
+    return Arrays.copyOf(orig, orig.length);
+  }
+
+  private <K, V> void setMap(Map<K, V> map, K[] keys, V[] values) {
+    assert(keys.length == values.length);
+    for (int i = 0; i < keys.length; i++) {
+      map.put(keys[i], values[i]);
+    }
+  }
+
+  private <K, V> void assertMapSet(
+      Map<K, V> map, K[] keys, V[] values) throws Exception {
+    assert(keys.length == values.length);
+    for (int i = 0; i < values.length; i++) {
+      assertEquals(values[i], map.get(keys[i]));
+    }
+    assertEquals(keys.length, map.size());
+  }
+
+  private void setMapMessage(TestMap testMap) {
+    testMap.int32ToInt32Field = new HashMap<Integer, Integer>();
+    testMap.int32ToBytesField = new HashMap<Integer, byte[]>();
+    testMap.int32ToEnumField = new HashMap<Integer, Integer>();
+    testMap.int32ToMessageField =
+        new HashMap<Integer, MapTestProto.TestMap.MessageValue>();
+    testMap.int32ToStringField = new HashMap<Integer, String>();
+    testMap.stringToInt32Field = new HashMap<String, Integer>();
+    testMap.boolToBoolField = new HashMap<Boolean, Boolean>();
+    testMap.uint32ToUint32Field = new HashMap<Integer, Integer>();
+    testMap.sint32ToSint32Field = new HashMap<Integer, Integer>();
+    testMap.fixed32ToFixed32Field = new HashMap<Integer, Integer>();
+    testMap.sfixed32ToSfixed32Field = new HashMap<Integer, Integer>();
+    testMap.int64ToInt64Field = new HashMap<Long, Long>();
+    testMap.uint64ToUint64Field = new HashMap<Long, Long>();
+    testMap.sint64ToSint64Field = new HashMap<Long, Long>();
+    testMap.fixed64ToFixed64Field = new HashMap<Long, Long>();
+    testMap.sfixed64ToSfixed64Field = new HashMap<Long, Long>();
+    setMap(testMap.int32ToInt32Field, int32Values, int32Values);
+    setMap(testMap.int32ToBytesField, int32Values, bytesValues);
+    setMap(testMap.int32ToEnumField, int32Values, enumValues);
+    setMap(testMap.int32ToMessageField, int32Values, messageValues);
+    setMap(testMap.int32ToStringField, int32Values, stringValues);
+    setMap(testMap.stringToInt32Field, stringValues, int32Values);
+    setMap(testMap.boolToBoolField, boolValues, boolValues);
+    setMap(testMap.uint32ToUint32Field, int32Values, int32Values);
+    setMap(testMap.sint32ToSint32Field, int32Values, int32Values);
+    setMap(testMap.fixed32ToFixed32Field, int32Values, int32Values);
+    setMap(testMap.sfixed32ToSfixed32Field, int32Values, int32Values);
+    setMap(testMap.int64ToInt64Field, int64Values, int64Values);
+    setMap(testMap.uint64ToUint64Field, int64Values, int64Values);
+    setMap(testMap.sint64ToSint64Field, int64Values, int64Values);
+    setMap(testMap.fixed64ToFixed64Field, int64Values, int64Values);
+    setMap(testMap.sfixed64ToSfixed64Field, int64Values, int64Values);
+  }
+  private void assertMapMessageSet(TestMap testMap) throws Exception {
+    assertMapSet(testMap.int32ToInt32Field, int32Values, int32Values);
+    assertMapSet(testMap.int32ToBytesField, int32Values, bytesValues);
+    assertMapSet(testMap.int32ToEnumField, int32Values, enumValues);
+    assertMapSet(testMap.int32ToMessageField, int32Values, messageValues);
+    assertMapSet(testMap.int32ToStringField, int32Values, stringValues);
+    assertMapSet(testMap.stringToInt32Field, stringValues, int32Values);
+    assertMapSet(testMap.boolToBoolField, boolValues, boolValues);
+    assertMapSet(testMap.uint32ToUint32Field, int32Values, int32Values);
+    assertMapSet(testMap.sint32ToSint32Field, int32Values, int32Values);
+    assertMapSet(testMap.fixed32ToFixed32Field, int32Values, int32Values);
+    assertMapSet(testMap.sfixed32ToSfixed32Field, int32Values, int32Values);
+    assertMapSet(testMap.int64ToInt64Field, int64Values, int64Values);
+    assertMapSet(testMap.uint64ToUint64Field, int64Values, int64Values);
+    assertMapSet(testMap.sint64ToSint64Field, int64Values, int64Values);
+    assertMapSet(testMap.fixed64ToFixed64Field, int64Values, int64Values);
+    assertMapSet(testMap.sfixed64ToSfixed64Field, int64Values, int64Values);
+  }
+
   private void assertRepeatedPackablesEqual(
       NanoRepeatedPackables.NonPacked nonPacked, NanoRepeatedPackables.Packed packed) {
     // Not using MessageNano.equals() -- that belongs to a separate test.
diff --git a/javanano/src/test/java/com/google/protobuf/nano/map_test.proto b/javanano/src/test/java/com/google/protobuf/nano/map_test.proto
new file mode 100644
index 00000000..f72833ad
--- /dev/null
+++ b/javanano/src/test/java/com/google/protobuf/nano/map_test.proto
@@ -0,0 +1,70 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+syntax = "proto3";
+
+package map_test;
+
+option java_package = "com.google.protobuf.nano";
+option java_outer_classname = "MapTestProto";
+
+message TestMap {
+  message MessageValue {
+    int32 value = 1;
+    int32 value2 = 2;
+  }
+  enum EnumValue {
+    FOO = 0;
+    BAR = 1;
+    BAZ = 2;
+    QUX = 3;
+  }
+
+  map<int32, int32>        int32_to_int32_field = 1;
+  map<int32, string>       int32_to_string_field = 2;
+  map<int32, bytes>        int32_to_bytes_field = 3;
+  map<int32, EnumValue>    int32_to_enum_field = 4;
+  map<int32, MessageValue> int32_to_message_field = 5;
+  map<string, int32>       string_to_int32_field = 6;
+  map<bool, bool>          bool_to_bool_field = 7;
+
+  // Test all the other primitive types. As the key and value are not coupled in
+  // the implementation, we do not test all the combinations of key/value pairs,
+  // so that we can keep the number of test cases manageable
+  map<uint32, uint32>      uint32_to_uint32_field = 11;
+  map<sint32, sint32>      sint32_to_sint32_field = 12;
+  map<fixed32, fixed32>    fixed32_to_fixed32_field = 13;
+  map<sfixed32, sfixed32>  sfixed32_to_sfixed32_field = 14;
+  map<int64, int64>        int64_to_int64_field = 15;
+  map<uint64, uint64>      uint64_to_uint64_field = 16;
+  map<sint64, sint64>      sint64_to_sint64_field = 17;
+  map<fixed64, fixed64>    fixed64_to_fixed64_field = 18;
+  map<sfixed64, sfixed64>  sfixed64_to_sfixed64_field = 19;
+}
diff --git a/src/Makefile.am b/src/Makefile.am
index 6fd8bd2b..0f0bd089 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -243,26 +243,28 @@ libprotoc_la_SOURCES =                                         \
   google/protobuf/compiler/java/java_doc_comment.cc            \
   google/protobuf/compiler/java/java_doc_comment.h             \
   google/protobuf/compiler/javanano/javanano_enum.cc           \
+  google/protobuf/compiler/javanano/javanano_enum.h            \
+  google/protobuf/compiler/javanano/javanano_enum_field.cc     \
   google/protobuf/compiler/javanano/javanano_enum_field.h      \
   google/protobuf/compiler/javanano/javanano_extension.cc      \
+  google/protobuf/compiler/javanano/javanano_extension.h       \
   google/protobuf/compiler/javanano/javanano_field.cc          \
+  google/protobuf/compiler/javanano/javanano_field.h           \
   google/protobuf/compiler/javanano/javanano_file.cc           \
+  google/protobuf/compiler/javanano/javanano_file.h            \
   google/protobuf/compiler/javanano/javanano_generator.cc      \
+  google/protobuf/compiler/javanano/javanano_generator.h       \
   google/protobuf/compiler/javanano/javanano_helpers.cc        \
+  google/protobuf/compiler/javanano/javanano_helpers.h         \
+  google/protobuf/compiler/javanano/javanano_map_field.cc      \
+  google/protobuf/compiler/javanano/javanano_map_field.h       \
   google/protobuf/compiler/javanano/javanano_message.cc        \
+  google/protobuf/compiler/javanano/javanano_message.h         \
+  google/protobuf/compiler/javanano/javanano_message_field.cc  \
   google/protobuf/compiler/javanano/javanano_message_field.h   \
   google/protobuf/compiler/javanano/javanano_params.h          \
-  google/protobuf/compiler/javanano/javanano_primitive_field.h \
-  google/protobuf/compiler/javanano/javanano_enum_field.cc     \
-  google/protobuf/compiler/javanano/javanano_enum.h            \
-  google/protobuf/compiler/javanano/javanano_extension.h       \
-  google/protobuf/compiler/javanano/javanano_field.h           \
-  google/protobuf/compiler/javanano/javanano_file.h            \
-  google/protobuf/compiler/javanano/javanano_generator.h       \
-  google/protobuf/compiler/javanano/javanano_helpers.h         \
-  google/protobuf/compiler/javanano/javanano_message_field.cc  \
-  google/protobuf/compiler/javanano/javanano_message.h         \
   google/protobuf/compiler/javanano/javanano_primitive_field.cc \
+  google/protobuf/compiler/javanano/javanano_primitive_field.h \
   google/protobuf/compiler/python/python_generator.cc          \
   google/protobuf/compiler/ruby/ruby_generator.cc
 
diff --git a/src/google/protobuf/compiler/javanano/javanano_field.cc b/src/google/protobuf/compiler/javanano/javanano_field.cc
index e3e4cefe..b9be90b1 100644
--- a/src/google/protobuf/compiler/javanano/javanano_field.cc
+++ b/src/google/protobuf/compiler/javanano/javanano_field.cc
@@ -36,6 +36,7 @@
 #include <google/protobuf/compiler/javanano/javanano_helpers.h>
 #include <google/protobuf/compiler/javanano/javanano_primitive_field.h>
 #include <google/protobuf/compiler/javanano/javanano_enum_field.h>
+#include <google/protobuf/compiler/javanano/javanano_map_field.h>
 #include <google/protobuf/compiler/javanano/javanano_message_field.h>
 #include <google/protobuf/stubs/common.h>
 
@@ -97,7 +98,11 @@ FieldGenerator* FieldGeneratorMap::MakeGenerator(const FieldDescriptor* field,
   if (field->is_repeated()) {
     switch (java_type) {
       case JAVATYPE_MESSAGE:
-        return new RepeatedMessageFieldGenerator(field, params);
+        if (IsMapEntry(field->message_type())) {
+          return new MapFieldGenerator(field, params);
+        } else {
+          return new RepeatedMessageFieldGenerator(field, params);
+        }
       case JAVATYPE_ENUM:
         return new RepeatedEnumFieldGenerator(field, params);
       default:
diff --git a/src/google/protobuf/compiler/javanano/javanano_helpers.cc b/src/google/protobuf/compiler/javanano/javanano_helpers.cc
index 2149418a..7b23d9f4 100644
--- a/src/google/protobuf/compiler/javanano/javanano_helpers.cc
+++ b/src/google/protobuf/compiler/javanano/javanano_helpers.cc
@@ -560,6 +560,17 @@ void SetBitOperationVariables(const string name,
   (*variables)["different_" + name] = GenerateDifferentBit(bitIndex);
 }
 
+bool HasMapField(const Descriptor* descriptor) {
+  for (int i = 0; i < descriptor->field_count(); ++i) {
+    const FieldDescriptor* field = descriptor->field(i);
+    if (field->type() == FieldDescriptor::TYPE_MESSAGE &&
+        IsMapEntry(field->message_type())) {
+      return true;
+    }
+  }
+  return false;
+}
+
 }  // namespace javanano
 }  // namespace compiler
 }  // namespace protobuf
diff --git a/src/google/protobuf/compiler/javanano/javanano_helpers.h b/src/google/protobuf/compiler/javanano/javanano_helpers.h
index 29310743..b4fee649 100644
--- a/src/google/protobuf/compiler/javanano/javanano_helpers.h
+++ b/src/google/protobuf/compiler/javanano/javanano_helpers.h
@@ -181,6 +181,14 @@ string GenerateDifferentBit(int bit_index);
 void SetBitOperationVariables(const string name,
     int bitIndex, map<string, string>* variables);
 
+inline bool IsMapEntry(const Descriptor* descriptor) {
+  // TODO(liujisi): Add an option to turn on maps for proto2 syntax as well.
+  return descriptor->options().map_entry() &&
+      descriptor->file()->syntax() == FileDescriptor::SYNTAX_PROTO3;
+}
+
+bool HasMapField(const Descriptor* descriptor);
+
 }  // namespace javanano
 }  // namespace compiler
 }  // namespace protobuf
diff --git a/src/google/protobuf/compiler/javanano/javanano_map_field.cc b/src/google/protobuf/compiler/javanano/javanano_map_field.cc
new file mode 100644
index 00000000..83b2b0ce
--- /dev/null
+++ b/src/google/protobuf/compiler/javanano/javanano_map_field.cc
@@ -0,0 +1,186 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// http://code.google.com/p/protobuf/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#include <google/protobuf/compiler/javanano/javanano_map_field.h>
+#include <google/protobuf/compiler/javanano/javanano_helpers.h>
+#include <google/protobuf/stubs/common.h>
+#include <google/protobuf/io/printer.h>
+#include <google/protobuf/wire_format.h>
+#include <google/protobuf/stubs/strutil.h>
+
+namespace google {
+namespace protobuf {
+namespace compiler {
+namespace javanano {
+
+namespace {
+
+string TypeName(const Params& params, const FieldDescriptor* field,
+                bool boxed) {
+  JavaType java_type = GetJavaType(field);
+  switch (java_type) {
+    case JAVATYPE_MESSAGE:
+      return ClassName(params, field->message_type());
+    case JAVATYPE_INT:
+    case JAVATYPE_LONG:
+    case JAVATYPE_FLOAT:
+    case JAVATYPE_DOUBLE:
+    case JAVATYPE_BOOLEAN:
+    case JAVATYPE_STRING:
+    case JAVATYPE_BYTES:
+    case JAVATYPE_ENUM:
+      if (boxed) {
+        return BoxedPrimitiveTypeName(java_type);
+      } else {
+        return PrimitiveTypeName(java_type);
+      }
+    // No default because we want the compiler to complain if any new JavaTypes
+    // are added..
+  }
+
+  GOOGLE_LOG(FATAL) << "should not reach here.";
+  return "";
+}
+
+const FieldDescriptor* KeyField(const FieldDescriptor* descriptor) {
+  GOOGLE_CHECK_EQ(FieldDescriptor::TYPE_MESSAGE, descriptor->type());
+  const Descriptor* message = descriptor->message_type();
+  GOOGLE_CHECK(message->options().map_entry());
+  return message->FindFieldByName("key");
+}
+
+const FieldDescriptor* ValueField(const FieldDescriptor* descriptor) {
+  GOOGLE_CHECK_EQ(FieldDescriptor::TYPE_MESSAGE, descriptor->type());
+  const Descriptor* message = descriptor->message_type();
+  GOOGLE_CHECK(message->options().map_entry());
+  return message->FindFieldByName("value");
+}
+
+void SetMapVariables(const Params& params,
+    const FieldDescriptor* descriptor, map<string, string>* variables) {
+  const FieldDescriptor* key = KeyField(descriptor);
+  const FieldDescriptor* value = ValueField(descriptor);
+  (*variables)["name"] =
+    RenameJavaKeywords(UnderscoresToCamelCase(descriptor));
+  (*variables)["number"] = SimpleItoa(descriptor->number());
+  (*variables)["key_type"] = TypeName(params, key, false);
+  (*variables)["boxed_key_type"] = TypeName(params,key, true);
+  (*variables)["key_desc_type"] =
+      "TYPE_" + ToUpper(FieldDescriptor::TypeName(key->type()));
+  (*variables)["key_tag"] = SimpleItoa(internal::WireFormat::MakeTag(key));
+  (*variables)["value_type"] = TypeName(params, value, false);
+  (*variables)["boxed_value_type"] = TypeName(params, value, true);
+  (*variables)["value_desc_type"] =
+      "TYPE_" + ToUpper(FieldDescriptor::TypeName(value->type()));
+  (*variables)["value_tag"] = SimpleItoa(internal::WireFormat::MakeTag(value));
+  (*variables)["type_parameters"] =
+      (*variables)["boxed_key_type"] + ", " + (*variables)["boxed_value_type"];
+  (*variables)["value_default"] =
+      value->type() == FieldDescriptor::TYPE_MESSAGE
+          ? "new " + (*variables)["value_type"] + "()"
+          : "null";
+}
+}  // namespace
+
+// ===================================================================
+MapFieldGenerator::MapFieldGenerator(const FieldDescriptor* descriptor,
+                                     const Params& params)
+    : FieldGenerator(params), descriptor_(descriptor) {
+  SetMapVariables(params, descriptor, &variables_);
+}
+
+MapFieldGenerator::~MapFieldGenerator() {}
+
+void MapFieldGenerator::
+GenerateMembers(io::Printer* printer, bool /* unused lazy_init */) const {
+  printer->Print(variables_,
+    "public java.util.Map<$type_parameters$> $name$;\n");
+}
+
+void MapFieldGenerator::
+GenerateClearCode(io::Printer* printer) const {
+  printer->Print(variables_,
+    "$name$ = null;\n");
+}
+
+void MapFieldGenerator::
+GenerateMergingCode(io::Printer* printer) const {
+  printer->Print(variables_,
+    "this.$name$ = com.google.protobuf.nano.InternalNano.mergeMapEntry(\n"
+    "  input, this.$name$, mapFactory,\n"
+    "  com.google.protobuf.nano.InternalNano.$key_desc_type$,\n"
+    "  com.google.protobuf.nano.InternalNano.$value_desc_type$,\n"
+    "  $value_default$,\n"
+    "  $key_tag$, $value_tag$);\n"
+    "\n");
+}
+
+void MapFieldGenerator::
+GenerateSerializationCode(io::Printer* printer) const {
+  printer->Print(variables_,
+    "if (this.$name$ != null) {\n"
+    "  com.google.protobuf.nano.InternalNano.serializeMapField(\n"
+    "    output, this.$name$, $number$,\n"
+    "  com.google.protobuf.nano.InternalNano.$key_desc_type$,\n"
+    "  com.google.protobuf.nano.InternalNano.$value_desc_type$);\n"
+    "}\n");
+}
+
+void MapFieldGenerator::
+GenerateSerializedSizeCode(io::Printer* printer) const {
+  printer->Print(variables_,
+    "if (this.$name$ != null) {\n"
+    "  size += com.google.protobuf.nano.InternalNano.computeMapFieldSize(\n"
+    "    this.$name$, $number$,\n"
+    "  com.google.protobuf.nano.InternalNano.$key_desc_type$,\n"
+    "  com.google.protobuf.nano.InternalNano.$value_desc_type$);\n"
+    "}\n");
+}
+
+void MapFieldGenerator::
+GenerateEqualsCode(io::Printer* printer) const {
+  printer->Print(variables_,
+    "if (!com.google.protobuf.nano.InternalNano.equals(\n"
+    "  this.$name$, other.$name$)) {\n"
+    "  return false;\n"
+    "}\n");
+}
+
+void MapFieldGenerator::
+GenerateHashCodeCode(io::Printer* printer) const {
+  printer->Print(variables_,
+    "result = 31 * result +\n"
+    "    com.google.protobuf.nano.InternalNano.hashCode(this.$name$);\n");
+}
+
+}  // namespace javanano
+}  // namespace compiler
+}  // namespace protobuf
+}  // namespace google
diff --git a/src/google/protobuf/compiler/javanano/javanano_map_field.h b/src/google/protobuf/compiler/javanano/javanano_map_field.h
new file mode 100644
index 00000000..c01bde38
--- /dev/null
+++ b/src/google/protobuf/compiler/javanano/javanano_map_field.h
@@ -0,0 +1,70 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// http://code.google.com/p/protobuf/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#ifndef GOOGLE_PROTOBUF_COMPILER_JAVANANO_MAP_FIELD_H__
+#define GOOGLE_PROTOBUF_COMPILER_JAVANANO_MAP_FIELD_H__
+
+#include <map>
+#include <string>
+#include <vector>
+#include <google/protobuf/compiler/javanano/javanano_field.h>
+
+namespace google {
+namespace protobuf {
+namespace compiler {
+namespace javanano {
+
+class MapFieldGenerator : public FieldGenerator {
+ public:
+  explicit MapFieldGenerator(
+      const FieldDescriptor* descriptor, const Params& params);
+  ~MapFieldGenerator();
+
+  // implements FieldGenerator ---------------------------------------
+  void GenerateMembers(io::Printer* printer, bool lazy_init) const;
+  void GenerateClearCode(io::Printer* printer) const;
+  void GenerateMergingCode(io::Printer* printer) const;
+  void GenerateSerializationCode(io::Printer* printer) const;
+  void GenerateSerializedSizeCode(io::Printer* printer) const;
+  void GenerateEqualsCode(io::Printer* printer) const;
+  void GenerateHashCodeCode(io::Printer* printer) const;
+
+ private:
+  const FieldDescriptor* descriptor_;
+  map<string, string> variables_;
+
+  GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(MapFieldGenerator);
+};
+
+}  // namespace javanano
+}  // namespace compiler
+}  // namespace protobuf
+}  // namespace google
+#endif  // GOOGLE_PROTOBUF_COMPILER_JAVANANO_MAP_FIELD_H__
diff --git a/src/google/protobuf/compiler/javanano/javanano_message.cc b/src/google/protobuf/compiler/javanano/javanano_message.cc
index 7c52ca31..da7c656f 100644
--- a/src/google/protobuf/compiler/javanano/javanano_message.cc
+++ b/src/google/protobuf/compiler/javanano/javanano_message.cc
@@ -90,6 +90,7 @@ void MessageGenerator::GenerateStaticVariables(io::Printer* printer) {
   // Generate static members for all nested types.
   for (int i = 0; i < descriptor_->nested_type_count(); i++) {
     // TODO(kenton):  Reuse MessageGenerator objects?
+    if (IsMapEntry(descriptor_->nested_type(i))) continue;
     MessageGenerator(descriptor_->nested_type(i), params_)
       .GenerateStaticVariables(printer);
   }
@@ -100,6 +101,7 @@ void MessageGenerator::GenerateStaticVariableInitializers(
   // Generate static member initializers for all nested types.
   for (int i = 0; i < descriptor_->nested_type_count(); i++) {
    // TODO(kenton):  Reuse MessageGenerator objects?
+    if (IsMapEntry(descriptor_->nested_type(i))) continue;
     MessageGenerator(descriptor_->nested_type(i), params_)
       .GenerateStaticVariableInitializers(printer);
   }
@@ -159,6 +161,7 @@ void MessageGenerator::Generate(io::Printer* printer) {
   }
 
   for (int i = 0; i < descriptor_->nested_type_count(); i++) {
+    if (IsMapEntry(descriptor_->nested_type(i))) continue;
     MessageGenerator(descriptor_->nested_type(i), params_).Generate(printer);
   }
 
@@ -342,6 +345,11 @@ void MessageGenerator::GenerateMergeFromMethods(io::Printer* printer) {
     "classname", descriptor_->name());
 
   printer->Indent();
+  if (HasMapField(descriptor_)) {
+    printer->Print(
+      "com.google.protobuf.nano.MapFactories.MapFactory mapFactory =\n"
+      "  com.google.protobuf.nano.MapFactories.getMapFactory();\n");
+  }
 
   printer->Print(
     "while (true) {\n");