java中对象转json,json转list，json转map
在IDEA中的springboot项⽬⾥写的⼀个测试例⼦，新建User类，四个字段，Long id ， String password，String userName，int age; 以及带参构造，toString⽅法在l中添加 net.sf.json-lib 依赖：
1<!-- 对象转json依赖包 -->
2<!-- mvnrepository/artifact/net.sf.json-lib/json-lib -->
json转换对象3<dependency>
4<groupId>net.sf.json-lib</groupId>
5<artifactId>json-lib</artifactId>
6<version>2.4</version>
7<!--不加下⾯这⼀项会报错，是因为json-lib⽀持版本是jdk1.5，所以要指定下版本-->
8<classifier>jdk15</classifier>
9</dependency>
json转换测试类：
1package com.lch.springboot04.jsonparse;
2
3import com.lch.springboot04.domain.User;
4import net.sf.json.JSONArray;
5import net.sf.json.JSONObject;
6
7import java.util.*;
8
9/**
10 * 对象转换为json数据测试，通过net.sf.json-lib.jar
11*/
12public class JsonParse {
13
14public static void main(String[] args) {
15/**
16 * object 转为json数组 ：数组，对象，map,list,list<Map<String,Object>> 都可以；
17 * object 转为json字符串：只有⾃定义对象和 map可以转换，其他都不能这样转；
18*/
19
20 String[] arr = {"a", "b", "c"};
21 System.out.println("string数组转为json数组" + JSONArray.fromObject(arr)); //["a","b","c"]
22// System.out.println("string数组转为json字符串"+ JSONObject.fromObject(arr).toString()); //⽆法转换：'object' is an array. Use JSONArray instead
23
24//java⾃定义对象转json
25 User jack = new User("123", "jack", 18);
26 System.out.println("Java对象转为json数组" + JSONArray.fromObject(jack));
27//结果：[{"age":18,"id":0,"password":"123","userName":"jack"}]
28 System.out.println("Java对象转为json字符串" + JSONObject.fromObject(jack).toString());
29//结果：{"age":18,"id":0,"password":"123","userName":"jack"}
30
31//list转json
32 User tom = new User("456", "tom", 20);
33 List<User> userList = new ArrayList<>();
34 userList.add(jack);
35 userList.add(tom);
36 System.out.println("list转为json数组" + JSONArray.fromObject(userList));
37// 结果：list转为json数组[{"age":18,"id":0,"password":"123","userName":"jack"},{"age":20,"id":0,"password":"456","userName":"tom"}]
38// System.out.println("list转为json字符串"+ JSONObject.fromObject(userList).toString()); //不能转为json字符串
39
40// list<Map<String,Object>> 转json
41 List<Map<String, Object>> mapList = new ArrayList();
42 Map<String, Object> m1 = new HashMap<String, Object>();
43 m1.put("jack", jack);
44 m1.put("tom", tom);
45 Map<String, Object> m2 = new HashMap<String, Object>();
46 m2.put("alex", new User("789", "alex", 20));
47 mapList.add(m1);
48 mapList.add(m2);
49 System.out.println("map转json数组" + JSONArray.fromObject(m2));
50// 转换结果：[{"alex":{"age":20,"id":0,"password":"789","userName":"alex"}}]
51 System.out.println("map转json字符串" + JSONObject.fromObject(m2));
52//结果：{"alex":{"age":20,"id":0,"password":"789","userName":"alex"}}
53 System.out.println(" list<Map<String,Object>> 转json数组" + JSONArray.fromObject(mapList));
54// 结果：[{"tom":{"age":20,"id":0,"password":"456","userName":"tom"},"jack":{"age":18,"id":0,"password":"123","userName":"jack"}},{"alex":{"age":20,"id":0,"password":"789","userName":"alex"}}] 55// System.out.println(" list<Map<String,Object>> 转json字符串"+JSONObject.fromObject(mapList));//不能转，'object' is an array. Use JSONArray instead
56
57/**
58 * json字符串转map
59*/
60/* String jsonStr = "{\"alex\":{\"age\":20,\"id\":0,\"password\":\"789\",\"userName\":\"alex\"}}";
61 Map<String,Object> map = jsonToMap(JSONObject.fromObject(jsonStr).get("alex").toString());
62 System.out.println("json字符串转map:"+("age"));*/
63// {"total":2,"items":[{"age":15,"id":1,"name":"jack"},{"age":16,"id":2,"name":"tom"}]}
64 String jsonStr2 = "{\"total\":2,\"items\":[{\"age\":15,\"id\":1,\"userName\":\"jack\"},{\"age\":16,\"id\":2,\"userName\":\"tom\"}]}";
65 Map<String, Object> stringObjectMap = jsonToMap(jsonStr2);
66for (Map.Entry<String, Object> entry : Set()) {
67 System.out.Key() + "--" + Value());
68 }
69/**输出结果：
70 * total--2
71 items--[{"age":15,"id":1,"userName":"jack"},{"age":16,"id":2,"userName":"tom"}]
72*/
73
74// jsonstr转list,list中存放Java Bean
75 String jsonStr3 = JSONObject.fromObject(jsonStr2).get("items").toString();
76 System.out.println("jsonStr3=" + jsonStr3);
77 List list = jsonStr2ObjectList(jsonStr3, User.class);
78for (Object u : list) {
79 System.out.println(u);
80 }
81/**
82 * 输出User{id=1, password='null', userName='jack', age=15}
83 User{id=2, password='null', userName='tom', age=16}
84*/
85
86 }
87
88/**
89 * json字符串转map 90 *
91 * @param jsonStr
92 * @return
93*/
94public static Map<String, Object> jsonToMap(String jsonStr) {
95 JSONObject jsonObject = JSONObject.fromObject(jsonStr); //⾸先转换为 JSONObject
96 Iterator<String> nameItr = jsonObject.keys();//获取jsonObject的keySet()的迭代器
97 String key;//接收key值
98 Map<String, Object> outMap = new HashMap<>(); //存放转换结果
99while (nameItr.hasNext()) {
100 key = ();
101 outMap.put(key, (key));
102 }
103return outMap;
104 }
105
106/**
107 * JSONObject类中keys()⽅法默认返回jsonObject的keyset的迭代器
108 * public Iterator keys() {
109 * this.verifyIsNull();
110 * return this.keySet().iterator();
111 * }
112*/
113
114/** json转list,list中存放JavaBean
115 * @param jsonStr 要转换的json字符串
116 * @param clazz javaBean的Class对象
117 * @return
118*/
119public static List jsonStr2ObjectList(String jsonStr, Class clazz) {
120 JSONArray array = JSONArray.fromObject(jsonStr);
121 List list = new ArrayList();
122for (Iterator itr = array.iterator(); itr.hasNext(); ) {
123 JSONObject jsonObject = (JSONObject) ();
124//取出json字符串中的⼀个⼦字符串，转换为指定类型的JavaBean
125 Object bean = Bean(jsonObject, clazz);
126 list.add(bean);
127 }
128return list;
129 }
130 }
结果：
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