JAVA array,map 转 json 字符串

public class User {
private String username;
private String password;
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
public String getPassword() {
return password;
}
public void setPassword(String password) {
this.password = password;
}
}

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);

来源：https://www.cnblogs.com/ceshi2016/p/6661525.html

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js json转字符串