Convert complex Java map to Json using Gson

Question

I'm trying to convert a Java Map (with a List of MyClass values) to json using gson.

Map<Integer, List<MyClass>> myMap

Here is how I am doing it...

Gson gson = new GsonBuilder().enableComplexMapKeySerialization().create();
String json = gson.toJson(myMap);
System.out.println(json);

It produces json that is close to, but not in the format I would expect/want. Here is what is produced:

{"0":[{MyClassItem1}, {MyClassItem2}, etc], "1":[{MyClassItem3}, {MyClassItem4}, etc], etc... }

I would expect/prefer it produces:

[{"0":[{MyClassItem1}, {MyClassItem2}, etc]}, {"1":[{MyClassItem3}, {MyClassItem4}, etc]}, etc...]

Is this possible? If so, how?

Answer 1

Well... Gson serializes data to its most appropriate form. It seems that you want an array of Map.Entry . Try something like:

Map<Integer, List<MyClass>> myMap = ...;
Set<Map.Entry<Integer, List<MyClass>>> entrySet = myMap.entrySet();
Object[] data = entrySet.toArray(new Object[entrySet.size()]);

// serialize data variable

However be aware that Gson might not be able to serialize Map.Entry out-of-the-box.