Gson.java

//For use Gson, you need a Gson jar. Download from this https://code.google.com/p/google-gson/
class Student {
	private String name;
	private int mark;
	private String city;
	
	public Student(String name, int mark, String city) {
		this.name = name;
		this.mark = mark;
		this.city = city;
	}

	@Override
	public String toString() {
		return "Student [name=" + name + ", mark=" + mark + "]";
	}
}
class Group {
	private ArrayList<Student> students;
	
	public Group() {
		students = new ArrayList<Student>();
	}
	public void add(Student s){
		students.add(s);
	}
	@Override
	public String toString() {
		return "Group [students=" + students + "]";
	}
}
//Use this for create json format or read json format
	String json;
	Gson gson = new GsonBuilder().setPrettyPrinting().create();
	Group g = new Group();
	g.add(new Student("John", 10, "Barcelona"));
	g.add(new Student("Daniel", 5, "Madrid"));
		
	json = gson.toJson(g);
	System.out.println(json);
		
	Group g2 = gson.fromJson(json, Group.class);
	System.out.println(g2);