Convert JSON to Nested Object (generic object) by using GSON

Question

I wanna create an parser for parse JSON by using Gson.

The first IParser.java

public interface IParser<T> {
    public T parse(String json);
}

The second Parser.java

import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import com.google.gson.reflect.TypeToken;

public class Parser<T> implements IParser<T> {

    @Override
    public T parse(String json) {
        GsonBuilder builder = new GsonBuilder();
        Gson gson = builder.enableComplexMapKeySerialization().create();
        MyJson<T> jsonParsed = gson.fromJson(json, new TypeToken<MyJson<T>>() {
        }.getType());

        System.out.println(jsonParsed.toString());
        return null;
    }

}

The third MyJson.java

public class MyJson<T> {
    private int status;
    private T data;

    public int getStatus() {
        return status;
    }

    public void setStatus(int status) {
        this.status = status;
    }

    public T getData() {
        return data;
    }

    public void setData(T data) {
        this.data = data;
    }
}

And User.java

import java.io.Serializable;

public class User implements Serializable {
    private static final long serialVersionUID = 1L;
    private long usrId;
    private String usrNm;
    private String usrPwd;
    private String usrEml;

    public User() {

    }

    public long getUsrId() {
        return usrId;
    }

    public void setUsrId(long usrId) {
        this.usrId = usrId;
    }

    public String getUsrNm() {
        return usrNm;
    }

    public void setUsrNm(String usrNm) {
        this.usrNm = usrNm;
    }

    public String getUsrPwd() {
        return usrPwd;
    }

    public void setUsrPwd(String usrPwd) {
        this.usrPwd = usrPwd;
    }

    public String getUsrEml() {
        return usrEml;
    }

    public void setUsrEml(String usrEml) {
        this.usrEml = usrEml;
    }

    @Override
    public String toString() {
        return "User [usrId=" + usrId + ", usrNm=" + usrNm + ", usrPwd="
                + usrPwd + ", usrEml=" + usrEml + "]";
    }
}

My JSON String:

{
    status: 200,
    data: {
        usrId: 2,
        usrNm: "John",
        usrPwd: "123",
        usrEml: "[email protected]"
    }
}

---

I wanna parse above jsonString to MyJson<T> object.

I do:

MyJson<T> jsonParsed = gson.fromJson(json, new TypeToken<MyJson<T>>() {
            }.getType());

=> Gson parses my User in MyJson to LinkedTreeMap

It mean: Object data = jsonParsed.getData(); => data instance of LinkedTreeMap

What I want: data instance of User

But, when I try:

MyJson<User> jsonParsed = gson.fromJson(json, new TypeToken<MyJson<User>>() {
            }.getType());

gson works fine.

So I wanna know that How can I make gson works fine with the first way (use T instead of User) because I wanna parse other object by using Parser

Thanks for your help.

Answer 1

@Override
public T parse(String json, Type type) {
    GsonBuilder builder = new GsonBuilder();
    Gson gson = builder.enableComplexMapKeySerialization().create();
    MyJson<T> jsonParsed = gson.fromJson(json, type);

    System.out.println(jsonParsed.toString());
    return null;
}

Using:

User user = myJson.parse(jsonString, new TypeToken<User>() {
        }.getType());