JavaBean,List,Map转成json格式

普通JavaBean(以User为例)转成json格式  1.转成JSONArray类型  User user = new User();  user.setUsername("cxl");  user.setPassword("1234");  JSONArray json = JSONArray.fromObject(user);  System.out.println(json);//[{"password":"1234","username":"cxl"}]  response.getWriter().print(json.toString());  在js文件取数据  $.getJSON("http://localhost:8080/jQueryDemo/servlet/UserServlet",null,function(data) {        alert(data[0].username);        alert(data[0].password);  });  2.转成JSONObject类型  JSONObject jsonObj = JSONObject.fromObject(user);  System.out.println(jsonObj);//{"password":"1234","username":"cxl"}  response.getWriter().print(jsonObj);  在js文件取数据  alert(data.username);  alert(data.password);  List转成json格式  List<User> users = new ArrayList<User>();  User user = new User();  user.setUsername("cxl");  user.setPassword("1234");  User u = new User();  u.setUsername("lhl");  u.setPassword("1234");  users.add(user);  users.add(u);  1.转成JSONArray类型  JSONArray json = JSONArray.fromObject(users);  System.out.println(json.toString());  //[{"password":"1234","username":"cxl"},{"password":"1234","username":"lhl"}]  response.getWriter().print(json.toString());  js中取数据：alert(alert(data[0].username));  2.转成JSONObject类型  不可直接使用JSONObject jsonObj = JSONObject.fromObject(users);  可通过下列方式  JSONObject jsonObj = new JSONObject();  jsonObj.put("users", users);  jsonObj.put("u", u);  System.out.println(jsonObj);  {"users":[{"password":"1234","username":"cxl"},{"password":"1234","username":"lhl"}],    "u":{"password":"1234","username":"lhl"}}  response.getWriter().print(jsonObj);  js中取数据：alert(data.users[0].username);             alert(data.u[0].username);  Map转成json格式  Map<String,Object> map = new HashMap<String,Object>();  map.put("users", users);  map.put("u", u);  1.转成JSONArray类型  JSONArray json = JSONArray.fromObject(map);  System.out.println(json.toString());//  [{"users":[{"password":"1234","username":"cxl"},{"password":"1234","username":"lhl"}],"u":{"password":"1234","username":"lhl"}}]  response.getWriter().print(json.toString);  js中取数据：alert(data[0].users[0].username);  2.转成JSONObject类型  JSONObject json = JSONObject.fromObject(map);  System.out.println(json);//  {"user":[{"password":"1234","username":"cxl"},{"password":"1234","username":"lhl"}],"u":{"password":"1234","username":"lhl"}}  response.getWriter().print(json);  js中取数据：alert(data.user[0].username);