Java Type Generic as Argument for GSON

Question

In GSON to get a list of objects you do

Gson gson = new Gson();
Type token = new TypeToken>(){}.getType();
return gson.fromJson(json         


        

Answer 1

This has been answered in previous questions. Basically, there are 2 options:

1. Pass the Type in from the calling site. The calling code will use TypeToken or whatever to construct it.
2. Construct a Type corresponding to the parameterized type yourself. This will require you to write a class that implements ParameterizedType

Answer 2

public static final <T> List<T> getList(final Class<T[]> clazz, final String json)
{
    final T[] jsonToObject = new Gson().fromJson(json, clazz);

    return Arrays.asList(jsonToObject);
}

Example:

getList(MyClass[].class, "[{...}]");

Answer 3

This work for everything. e.g. map which has a key and value generic.

CustomType type = new CustomType(Map.class, String.class, Integer.class);

So no more TokenType.

class CustomType implements ParameterizedType {
    private final Class<?> container;
    private final Class<?>[] wrapped;

    @Contract(pure = true)
    public CustomType(Class<?> container, Class<?>... wrapped) {
        this.container = container;
        this.wrapped = wrapped;
    }

    @Override
    public Type[] getActualTypeArguments() {
        return this.wrapped;
    }

    @Override
    public Type getRawType() {
        return this.container;
    }

    @Override
    public Type getOwnerType() {
        return null;
    }
}

Answer 4

  public static <T> T getObject(String gsonStr) {
        Gson gson = new GsonBuilder()
                .setLenient()
                .create();
        Type collectionType = new TypeToken< T>(){}.getType();
        return gson.fromJson(gsonStr,
                collectionType);
    }

When use:

Class1 class1=  getObject(jsonStr);

Answer 5

Since gson 2.8.0, you can use TypeToken#getParametized((Type rawType, Type... typeArguments)) to create the typeToken, then getType() should do the trick.

For example:

TypeToken.getParameterized(List.class, myType).getType();

Answer 6

Here is the full code base on great answer from @oldergod

public <T> List<T> fromJSonList(String json, Class<T> myType) {
    Gson gson = new Gson();
    Type collectionType = TypeToken.getParameterized(List.class, myType).getType();
    return gson.fromJson(json, collectionType);
}

Using

List<MyType> myTypes = parser.fromJSonList(jsonString, MyType.class);

Hope it help