How use generic T inside a method in java?

Question

We can do this in C#:

private T getData<T>(Context context, String url, PostModel postModel) throws ApiException, IOException, ConnectionException {
    Response response = new CallApi<T>(Connection.getApiUrl(context))
            .Post(url, postModel);    
    if (response.code() != 200) throw new ApiException(context,response);

    Gson gson = new GsonBuilder()
            .setLenient()
            .create();
    T obj = gson.fromJson(response.body().charStream(),
            new TypeToken<T>() {
            }.getType());
    return obj;
}

To call:

EmployeeModel model =  getData<EmployeeModel>(context, url, null);

As you can see we declare T as in method signature and inside the method, it replaced with EmployeeModel in CallApi<T> and new TypeToken<T> and it will return EmployeeModel object as the result.

In Java(Android) when I want to use this generic, I have:

private <T> T getData(Context context, String url, PostModel postModel){...}

But it returns me a LinkedTreeMap object and not an EmployeeModel! When I move < T > from method signature to the class itself result is same too.

I search the web and StackOverflow for finding this type of using but articles are just about how to cast T to a model or how to pass it as a parameter.

Please consider that I don't pass T into a method as a parameter and I don't need to cast T to anything. T is used as the type on other generic methods type!

So how can I implement this method in Java?

Answer 1

new TypeToken<T>() {} wouldn't work like you want it to, because of type erasure.

You would have to pass in a TypeToken<T> as a parameter:

EmployeeModel model = getData(
    context, url, null, new TypeToken<EmployeeModel>() {});

changing the method signature to add the extra parameter; then:

T obj = gson.fromJson(response.body().charStream(), typeToken);