Deserializing Generic Types with GSON

Question

I have some problems with implementation of Json Deserialization in my Android application (with Gson library)

I\'ve made class like this

public clas         


        

Answer 1

You have to specify the type of T at the time of deserialization. How would your List of posts get created if Gson didn't know what Type to instantiate? It can't stay T forever. So, you would provide the type T as a Class parameter.

Now assuming, the type of posts was String you would deserialize MyJson as (I've also added a String json parameter for simplicity; you would read from your reader as before):

doInBackground(String.class, "{posts: [\"article 1\", \"article 2\"]}");

protected MyJson doInBackground(Class type, String json, Void... params) {

    GsonBuilder gson = new GsonBuilder();
    Type collectionType = new TypeToken>(){}.getType();

    MyJson myJson = gson.create().fromJson(json, collectionType);

    System.out.println(myJson.getPosts()); // ["article 1", "article 2"]
    return myJson;
}

Similarly, to deserialize a MyJson of Boolean objects

doInBackground(Boolean.class, "{posts: [true, false]}");

protected MyJson doInBackground(Class type, String json, Void... params) {

    GsonBuilder gson = new GsonBuilder();
    Type collectionType = new TypeToken>(){}.getType();

    MyJson myJson = gson.create().fromJson(json, collectionType);

    System.out.println(myJson.getPosts()); // [true, false]
    return myJson;
}

I've assumed MyJson for my examples to be as

public class MyJson {

    public List posts;

    public List getPosts() {
        return posts;
    }
}

So, if you were looking for to deserialize a List you would invoke the method as

// assuming no Void parameters were required
MyJson myJson = doInBackground(MyObject.class);