Google Gson - deserialize list<class> object? (generic type)

Method to deserialize generic collection:

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

...

Type listType = new TypeToken<ArrayList<YourClass>>(){}.getType();
List<YourClass> yourClassList = new Gson().fromJson(jsonArray, listType);

Since several people in the comments have mentioned it, here's an explanation of how the TypeToken class is being used. The construction new TypeToken<...>() {}.getType() captures a compile-time type (between the < and >) into a runtime java.lang.reflect.Type object. Unlike a Class object, which can only represent a raw (erased) type, the Type object can represent any type in the Java language, including a parameterized instantiation of a generic type.

The TypeToken class itself does not have a public constructor, because you're not supposed to construct it directly. Instead, you always construct an anonymous subclass (hence the {}, which is a necessary part of this expression).

Due to type erasure, the TypeToken class is only able to capture types that are fully known at compile time. (That is, you can't do new TypeToken<List<T>>() {}.getType() for a type parameter T.)

For more information, see the documentation for the TypeToken class.

Another way is to use an array as a type, e.g.:

MyClass[] mcArray = gson.fromJson(jsonString, MyClass[].class);

This way you avoid all the hassle with the Type object, and if you really need a list you can always convert the array to a list by:

List<MyClass> mcList = Arrays.asList(mcArray);

IMHO this is much more readable.

And to make it be an actual list (that can be modified, see limitations of Arrays.asList()) then just do the following:

List<MyClass> mcList = new ArrayList<>(Arrays.asList(mcArray));

Since Gson 2.8, we can create util function like

public <T> List<T> getList(String jsonArray, Class<T> clazz) {
    Type typeOfT = TypeToken.getParameterized(List.class, clazz).getType();
    return new Gson().fromJson(jsonArray, typeOfT);
}

Example using

String jsonArray = ...
List<User> user = getList(jsonArray, User.class);