Gson TypeToken with dynamic ArrayList item type

Question

I have this code:

Type typeOfObjectsList = new TypeToken>() {}.getType();
List objectsList = new Gson().fromJso         


        

Answer 1

The syntax you are proposing is invalid. The following

new TypeToken<ArrayList<Class.forName(MyClass)>>

is invalid because you're trying to pass a method invocation where a type name is expected.

The following

new TypeToken<ArrayList<T>>() 

is not possible because of how generics (type erasure) and reflection works. The whole TypeToken hack works because Class#getGenericSuperclass() does the following

Returns the Type representing the direct superclass of the entity (class, interface, primitive type or void) represented by this Class.

If the superclass is a parameterized type, the Type object returned must accurately reflect the actual type parameters used in the source code.

In other words, if it sees ArrayList<T>, that's the ParameterizedType it will return and you won't be able to extract the compile time value that the type variable T would have had.

Type and ParameterizedType are both interfaces. You can provide an instance of your own implementation.

Answer 2

You can do this with Guava's more powerful TypeToken:

private static <T> Type setModelAndGetCorrespondingList2(Class<T> type) {
    return new TypeToken<ArrayList<T>>() {}
            .where(new TypeParameter<T>() {}, type)
            .getType();
}

Answer 3

sun.reflect.generics.reflectiveObjects.ParameterizedTypeImpl workes. No need for custom implementation

Type type = ParameterizedTypeImpl.make(List.class, new Type[]{childrenClazz}, null);
List list = gson.fromJson(json, type);

Can be used with maps and any other collection:

ParameterizedTypeImpl.make(Map.class, new Type[]{String.class, childrenClazz}, null);

Here is nice demo how you can use it in custom deserializer: Deserializing ImmutableList using Gson