Question

I am trying to create a utility class that accepts any type of POJO, and converts that POJO into a JSON object. It should use Java reflections and annotations to look through certain getter methods and create a key, value JSON element based on that.

I am trying to use generics to do this, but it doesn’t seem to work. Is this not possible?

I want to pass a class object as a parameter and retrieve the correct class methods if possible.

Code I have written so far:

package com.jr.freedom.util;

import java.lang.reflect.Field;
import java.lang.reflect.Method;
import net.sf.json.JSONObject;

public class JsonParserUtil {
    private static final String GET_CHAR_SEQUENCE = "get";

    public static <T> JSONObject toJsonObject(Class<T> classObject) {
        // get Method names with @JsonElement included
        Method methods[] = classObject.class.getDeclaredMethods();

        JSONObject jsonObject = new JSONObject();
        try {
            for (int i = 0; i < methods.length; i++) {
                String key = methods[i].getName();
                System.out.println(key);
                if (methods[i].isAnnotationPresent(JsonElement.class) && key.contains(GET_CHAR_SEQUENCE)) {
                    key.replaceFirst(GET_CHAR_SEQUENCE, "");
                    jsonObject.put(key, methods[i].invoke(classObject));
                }
            }
            return jsonObject;
        } catch (Exception e) {
            e.printStackTrace();
            return null;
        }
    }
}

Here is the testMethod that tries to use the above JSON util object

User user = new User();
user.setBio("bio mate");
user.setCountry("uk");
user.setEmailAddress("[e-mail]");
user.setFirstName("jono");
user.setPassword("passwordfdsadsa");
user.setUsername("crazy8");
JSONObject jsonUser =  new JsonParserUtil<User>().toJsonObject(user);

User class is a simple POJO with getters and setters. Currently this line: Method methods[] = T.class.getDeclaredMethods(); won’t work, as you can’t use the generic T to get the DeclaredMethods. Is there a way to do so? Or do I have to create this util method for every single POJO I make?

I know it will work using: Method methods[] = User.class.getDeclaredMethods(); but that will only be applicable for the User class. I am trying to create a util JSON class that can take any POJO object and try to create a JSONObject automatically.

Answer 1

Solution:

public static JSONObject toJsonObject(Object classObject) {
        // get Method names with @JsonElement included

        Method methods[] = classObject.getClass().getDeclaredMethods();

        JSONObject jsonObject = new JSONObject();
        try {
            for (int i = 0; i < methods.length; i++) {
                String key = methods[i].getName();
                System.out.println(key);
                if (methods[i].isAnnotationPresent(JsonElement.class) && key.startsWith(GET_CHAR_SEQUENCE)) {
                    key = key.replaceFirst(GET_CHAR_SEQUENCE, "");
                    jsonObject.put(key, methods[i].invoke(classObject));
                }

            }
            return jsonObject;
        } catch (Exception e) {
            e.printStackTrace();
            return null;
        }

    }

The key being to use

classObject.getClass()