How to Use Gson TypeToken with Dynamic ArrayList Item Types at Runtime?

Gson TypeToken with Dynamic ArrayList Item Type at Runtime

When working with JSON, it's common to convert JSON data into typed objects using Gson. However, you may encounter a scenario where the type of ArrayList item you need to parse is determined dynamically at runtime using reflection. In such cases, the traditional TypeToken approach may fall short.

For instance, consider this code:

Type typeOfObjectsList = new TypeToken<ArrayList<myClass>>() {}.getType();
List<myClass> objectsList = new Gson().fromJson(json, typeOfObjectsList);

This code converts a JSON string into a list of myClass objects. But what if the item type of the ArrayList should be determined dynamically?

To achieve this, you can leverage a new feature introduced in Gson version 2.8.0: TypeToken.getParameterized. This method allows you to create a TypeToken with a specified parameterized type.

Here's how you can use it:

private <T> Type setModelAndGetCorrespondingList2(Class<T> type) {
    Type typeOfObjectsListNew = TypeToken.getParameterized(ArrayList.class, type).getType();
    return typeOfObjectsListNew;
}

By passing the ArrayList class and the dynamic item type class type as arguments to TypeToken.getParameterized, you create a TypeToken that represents an ArrayList with the desired item type. This TypeToken can then be used as the parameter for Gson.fromJson to correctly parse the JSON data into the desired list type.

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