首先要帶入第三方工具類jar包 gson

1，普通類：

public void test() {
		//1、建立Gson物件
		Gson gson = new Gson();
		User user = new User(1, "liujinghan", "123456", "[email protected]");
		//2、呼叫toJson(Object)將物件轉為字串
		String json = gson.toJson(user);
		//{"id":1,"username":"liujinghan","password":"123456","email":"
 
[email protected]"}
		System.out.println(json);
		//3、將json字串封裝為java物件[json字串 的屬性名要和javabean的屬性一樣]
		User user2 = gson.fromJson(json, User.class);
		System.out.println(user2);
	}

2，Map陣列形式

public void test1() {
		Map map = new HashMap();
		map.put("name", "laolu");
		map.put("age", 18);
		Gson gson = new Gson();
		String json = gson.toJson(map);
		System.out.println(json);
		//將json字串轉為map   Gson將int型別資料轉換時會轉為double型別
		Map map2 = gson.fromJson(json, Map.class);
		System.out.println(map2);
		
	}
 

3，List陣列的形式：

public void test2() {
		List<User> list = new ArrayList<User>();
		list.add(new User(1, "liujinghan1", "123456", "[email protected]"));
		list.add(new User(2, "liujinghan2", "123456", "[email protected]"));
		list.add(new User(3, "liujinghan3", "123456", "[email protected]
 
"));
		list.add(new User(4, "liujinghan4", "123456", "[email protected]"));
		Gson gson = new Gson();
		//會將list轉為一個json陣列，每個元素就對應一個java物件
		String json = gson.toJson(list);
		System.out.println(json);
		List list2 = gson.fromJson(json,List.class);
		System.out.println(list2.get(0));