PrettyPrintJson.java

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

public class PrettyPrintJson
{
    public static void main(String[] args)
    {
        Person person = new Person();
        person.firstName = "John";
        person.lastName = "Stark";
        person.age = 32;
        person.nationality = "British";

        Gson gson = new Gson();
        String json = gson.toJson(person);
        System.out.println(json);

        //// OUTPUT
        /* {"firstName":"John","lastName":"Stark","age":32,"nationality":"British"} */

        Gson prettyGson = new GsonBuilder().setPrettyPrinting().create();
        String prettyJson = prettyGson.toJson(person);
        System.out.println(prettyJson);

        //// OUTPUT
        /*
        {
          "firstName": "John",
          "lastName": "Stark",
          "age": 32,
          "nationality": "British"
        }
        */
    }
}

class Person
{
    public String firstName;
    public String lastName;
    public int age;
    public String nationality;
}