How to use TreeMapSerializer ?

[Mr14huashao]

Kryo doesn't serialize the TreeMapSerializer comparator.
How to reproduce:

        HashMap map = new HashMap();
	map.put(1,122);
	map.put(2,314);
	map.put(4,2511);
	map.put(8,"hello");
	map.put(10,"wasted");
	map.put(3,"Great");
	TreeMap treeMap = new TreeMap(Comparator.reverseOrder());
	treeMap.putAll(map);
           
        final Kryo kryo = new Kryo();
	kryo.register(TreeMap.class, new DefaultSerializers.TreeMapSerializer());
	kryo.writeClassAndObject(output, treeMap);
	Object o = kryo.readClassAndObject(new Input(output.getBuffer()));

Did I use it wrong?
Thanks in advance

[theigl]

@Mr14huashao: What happens? An error message? Is the comparator null after deserialization?

I'm guessing the problem is with Comparator.reverseOrder() and not the TreeMapSerializer. reverseOrder() is basically a singleton and maybe can't be instantiated correctly.

[theigl]

You have to register the comparator as well. This test passes:

@Test
public void testTreeMapWithReverseComparator () {
  kryo.register(TreeMap.class);
  kryo.register(Comparator.reverseOrder().getClass());

  HashMap<Integer, Integer> map = new HashMap<>();
  map.put(1, 122);
  map.put(2, 314);
  map.put(4, 2511);

  TreeMap<Integer, Integer> treeMap = new TreeMap<>(Comparator.reverseOrder());
  treeMap.putAll(map);

  roundTrip(18, treeMap);
}

[Mr14huashao]

Thanks for your help! @theigl. Your code is available.
Now I want to add a ConcurrentSkipListMapSerializer.
Do you think it is necessary?

[Mr14huashao]

@theigl Thank you very much for your reply and check.
I update #763 and submit a new PR #768
Welcome to the PR to provide your valuable comments.