How Can I Use Gson's TypeToken with a Dynamically Determined ArrayList Item Type in Java?

Gson TypeToken with Dynamic ArrayList Item Type Using Reflection

In Java, Gson's TypeToken can be used to represent a parameterized type. In certain scenarios, it is necessary to dynamically specify the type of ArrayList items at runtime using reflection. This can be achieved as follows:

To specify the item type of an ArrayList at runtime, we can use the TypeToken#getParameterized method. This method accepts a raw type and a variable number of type arguments. In this case, we would use the raw type ArrayList.class and the dynamically determined type as the type argument.

For example, the following snippet demonstrates how to create a TypeToken with a dynamic ArrayList item type:

import com.google.gson.reflect.TypeToken;
import java.lang.reflect.Type;

public class Example {

    public static void main(String[] args) {
        // Dynamically determine the ArrayList item type
        Class<?> itemType = Class.forName("myPackage.myClass");

        // Create the TypeToken with the dynamic item type
        Type typeOfObjectsList = TypeToken.getParameterized(ArrayList.class, itemType).getType();

        // Use the TypeToken to convert a JSON string to a List of objects
        String json = "...";
        List<?> objectsList = new Gson().fromJson(json, typeOfObjectsList);
    }
}

In this example, itemType is determined dynamically at runtime, and the TypeToken is created using getParameterized. The resulting TypeToken can then be used to convert a JSON string to a List of objects with the specified item type.

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