Serializing HashMap By MessagePack for Java.

gistfile1.txt

@Test
public void testSerliazingMapByMessagePack(){
    Map<String, Object> map = new HashMap<String, Object>();
    map.put("int", 1);
    map.put("long", 1L);
    map.put("date", new Date());
    map.put("string", "test");

    byte[] buffer = MessagePack.pack(map);
    for (byte b : buffer) {
	      System.out.print(Integer.toHexString(b & 0xFF) + " ");
    }
    System.out.println();
    System.out.println("buffer.length: " + buffer.length);
    System.out.println();
    
    InputStream in = new ByteArrayInputStream(buffer);
    Unpacker unpacker = new Unpacker(in);
    
    for(Object obj : unpacker){
    	MapType mapType = (MapType)obj;
    	Map<MessagePackObject, MessagePackObject> ret = mapType.asMap();
    	for(MessagePackObject key : ret.keySet()){
    	    String keyStr = key.asString();
    	    Object value = ret.get(key);
    	    System.out.println(String.format("%s: %s", keyStr, value));
    	}
    }
}

result:
84 a3 69 6e 74 1 a6 73 74 72 69 6e 67 a4 74 65 73 74 a4 64 61 74 65 cf 0 0 1 32 59 9 51 f5 a4 6c 6f 6e 67 1
buffer.length: 38

int: org.msgpack.object.ShortIntegerTypeIMPL@1
long: org.msgpack.object.ShortIntegerTypeIMPL@1
date: org.msgpack.object.LongIntegerTypeIMPL@590950c7
string: org.msgpack.object.RawType@445c13

Which msgpack version are you using ? @masayuki038