gson是一个json库，它可以方便的转换java bean成json对象，也可以方便的将json对象转换为java bean。

比起官方的Lib,Gson除了提供原本的Json相关功能外,更包含了Json和Java Object的互相转换,而且许多常见的类型也可以转换，特別是collection集合,非常方便

其项目地址：https://code.google.com/p/google-gson/

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.Date;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

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

public class People {
    private int id;
    private String name;
    private float height;
    private double weight;
    private List friends = new ArrayList();
    private Map info = new HashMap();
    private Date birthday;
    private String comment;

    public People(){
        id = 123456;
        name = "Jacky";
        height = new Float(172.2);
        weight = new Double(61.236);
        friends.add("Sam");
        friends.add("Jimmy");
        info.put("country","Taiwan");
        info.put("city","Taipei");
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
        try {
            birthday = sdf.parse("1989-08-09");
        } catch (ParseException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        comment = null;
    }

    public String toString(){
        String str = "";
        str += "id="+id;
        str += " name="+name;
        str += " height="+height;
        str += " weight="+weight;
        str += " ...etc";
        return str;
    }

    public static void main(String[] args) {
        People p = new People();
        //Gson gson = new Gson();
        //If you wanna allow null object
        Gson gson = new GsonBuilder().serializeNulls().create();
        String str = gson.toJson(p);
        System.out.println(str);

        People p2 = gson.fromJson(str, People.class);
        System.out.println(p2.toString());
    }
}