Java Generics, Create an instance of Class<T>

Question

I am trying to write a generic method for deserializing json into my model. My problem is that I don't know how to get Class from the generic type T. My code looks something like this (and doesn't compile this way)

public class JsonHelper {

    public <T> T Deserialize(String json)
    {
        Gson gson = new Gson();

        return gson.fromJson(json, Class<T>);
    }
}

I tried something else, to get the type, but it throws an error I had the class as JsonHelper<T> and then tried this

Class<T> persistentClass = (Class<T>) ((ParameterizedType)getClass()
    .getGenericSuperclass())
    .getActualTypeArguments()[0];

The method signature looks like this

com.google.gson.Gson.fromJson(String json, Class<T> classOfT)

So, how can I translate along T so that when I call JsonHelper.Deserialize<MyObject>(json); I get an instance of the correct object?

Answer 1

You need to get a Class instance from somewhere. That is, your Deserialize() method needs to take a Class<T> as a parameter, just like the underlying fromJson() method.

Your method signature should look like Gson's:

<T> T Deserialize(String json, Class<T> type) ...

Your calls will look like this:

MyObject obj = helper.Deserialize(json, MyObject.class);

By the way, the convention to start method names with a lowercase letter is well established in Java.