GSON中Java对象与JSON互相转换——(一)

json的转换插件是通过java的一些工具，直接将java对象或集合转换成json字符串。

常用的json转换工具有如下几种：

1）jsonlib

2）Gson：google

3）fastjson：阿里巴巴

------GSON操作简单，只需要一个jar包----------

User.java

 1 package bean;
 2 
 3 public class User {
 4 
 5     private String id;
 6     private String name;
 7     private int age;
 8     private String address;
 9     public String getId() {
10         return id;
11     }
12     public void setId(String id) {
13         this.id = id;
14     }
15     public String getName() {
16         return name;
17     }
18     public void setName(String name) {
19         this.name = name;
20     }
21     public User(String id, String name, int age, String address) {
22         super();
23         this.id = id;
24         this.name = name;
25         this.age = age;
26         this.address = address;
27     }
28     @Override
29     public String toString() {
30         return "User [id=" + id + ", name=" + name + ", age=" + age + ", address=" + address + "]";
31     }
32     
33     
34     
35 }

1.测试Java对象转JSON(测试结果在后面注释)

操作简单，无论转单个对象还是集合，都是gson.toJson(obj);

 1 package TestJson;
 2 
 3 import java.util.ArrayList;
 4 import java.util.HashMap;
 5 import java.util.List;
 6 import java.util.Map;
 7 
 8 import javax.xml.bind.UnmarshallerHandler;
 9 
10 import org.junit.Test;
11 
12 import com.google.gson.Gson;
13 
14 import bean.User;
15 
16 public class Bean2JSON {
17 
18 //    测试单个对象转JSON
19     @Test
20     public void test1(){
21         User user = new User("1", "QIAOZHI",25,"山西太原");
22         Gson gson = new Gson();
23         String json = gson.toJson(user);
24         System.out.println(json);   //{"id":"1","name":"QIAOZHI","age":25,"address":"山西太原"}
25     }
26     
27     
28     
29 //    测试list转JSON
30     @Test
31     public void test2(){
32         List<User> list = new ArrayList<User>();
33         list.add(new User("1", "QIAOZHI",25,"山西太原"));
34         list.add(new User("2", "QIAOZHI",25,"山西太原"));
35         list.add(new User("3", "QIAOZHI",25,"山西太原"));
36         Gson gson = new Gson();
37         String json = gson.toJson(list);
38         System.out.println(json);
39 //        [{"id":"1","name":"QIAOZHI","age":25,"address":"山西太原"},{"id":"2","name":"QIAOZHI","age":25,"address":"山西太原"},{"id":"3","name":"QIAOZHI","age":25,"address":"山西太原"}]
40     }
41     
42 //    测试map对象转JSON
43     @Test
44     public void test3(){
45         Map<String,User> map = new HashMap<String,User>();
46         map.put("1", new User("1", "QIAOZHI",25,"山西太原"));
47         map.put("2", new User("2", "QIAOZHI",25,"山西太原"));
48         map.put("3", new User("3", "QIAOZHI",25,"山西太原"));
49         Gson gson = new Gson();
50         String json = gson.toJson(map);
51         System.out.println(json);
52 //        {"3":{"id":"3","name":"QIAOZHI","age":25,"address":"山西太原"},"2":{"id":"2","name":"QIAOZHI","age":25,"address":"山西太原"},"1":{"id":"1","name":"QIAOZHI","age":25,"address":"山西太原"}}
53     }
54     
55 //    测试list<map>对象转JSON
56     @Test
57     public void test4(){
58         List<Map<String,User>> list = new ArrayList<>();
59         Map<String,User> map1 = new HashMap<String,User>();
60         Map<String,User> map2 = new HashMap<String,User>();
61         map1.put("map11", new User("1", "QIAOZHI",25,"山西太原"));
62         map1.put("map12", new User("2", "QIAOZHI",25,"山西太原"));
63         map2.put("21", new User("11", "QIAOZHI",25,"山西太原"));
64         map2.put("22", new User("21", "QIAOZHI",25,"山西太原"));
65         list.add(map1);
66         list.add(map2);
67         Gson gson = new Gson();
68         String json = gson.toJson(list);
69         System.out.println(json);
70 //        [{"map12":{"id":"2","name":"QIAOZHI","age":25,"address":"山西太原"},"map11":{"id":"1","name":"QIAOZHI","age":25,"address":"山西太原"}},{"21":{"id":"11","name":"QIAOZHI","age":25,"address":"山西太原"},"22":{"id":"21","name":"QIAOZHI","age":25,"address":"山西太原"}}]
71     }
72     
73 }

 2.测试Json转Java对象与集合(测试结果在后面注释)

package TestJson_GSON;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import org.junit.Test;

import com.google.gson.Gson;
import com.google.gson.reflect.TypeToken;

public class JSON2Bean {
//    测试json转单个对象
    @Test
    public void test1(){
        String json = "{'id':'1','name':'QIAOZHI','age':25,'address':'山西太原'}";
        Gson gson = new Gson();
        User user = gson.fromJson(json, User.class);
        System.out.println(user);  
//        User [id=1, name=QIAOZHI, age=25, address=山西太原]
    }
    
    
    
//    测试JSON转list
    @SuppressWarnings("unchecked")
    @Test
    public void test2(){
        String json = "[{'id':'1','name':'QIAOZHI','age':25,'address':'山西太原'},{'id':'2','name':'QIAOZHI','age':25,'address':'山西太原'},{'id':'3','name':'QIAOZHI','age':25,'address':'山西太原'}]";
        List<User> list = new ArrayList<User>();
        Gson gson = new Gson();
        list = (List<User>) gson.fromJson(json, new TypeToken<List<User>>(){}.getType());
        System.out.println(list);
        for(User user:list){
            System.out.println(user);
        }
//        [{id=1, name=QIAOZHI, age=25.0, address=山西太原}, {id=2, name=QIAOZHI, age=25.0, address=山西太原}, {id=3, name=QIAOZHI, age=25.0, address=山西太原}]
        System.out.println(list.get(1));
//        {id=2, name=QIAOZHI, age=25.0, address=山西太原}
    }
    
    
//    测试JSON转Map
    @Test
    public void test3(){
        String json = "{'3':{'id':'3','name':'QIAOZHI','age':25,'address':'山西太原'},'2':{'id':'2','name':'QIAOZHI','age':25,'address':'山西太原'},'1':{'id':'1','name':'QIAOZHI','age':25,'address':'山西太原'}}";
        Map<String,User> map = new HashMap<String,User>();
        Gson gson = new Gson();
        map = (Map<String,User>) gson.fromJson(json, new TypeToken<Map<String,User>>(){}.getType());
        System.out.println(map);
//        {3={id=3, name=QIAOZHI, age=25.0, address=山西太原}, 2={id=2, name=QIAOZHI, age=25.0, address=山西太原}, 1={id=1, name=QIAOZHI, age=25.0, address=山西太原}}
        User user = map.get("1");
        System.out.println(user);
//        {id=1, name=QIAOZHI, age=25.0, address=山西太原}
    }
    
    
//    测试JSON转list<map>对象
    @SuppressWarnings("unchecked")
    @Test
    public void test4(){
        String json = "[{'map12':{'id':'2','name':'QIAOZHI','age':25,'address':'山西太原'},'map11':{'id':'1','name':'QIAOZHI','age':25,'address':'山西太原'}},{'21':{'id':'11','name':'QIAOZHI','age':25,'address':'山西太原'},'22':{'id':'21','name':'QIAOZHI','age':25,'address':'山西太原'}}]";
        List<Map<String,User>> list = new ArrayList<>();
        Gson gson = new Gson();
        list = gson.fromJson(json, new TypeToken<List<Map<String,User>>>(){}.getType());
        System.out.println(list);
//        [{map12={id=2, name=QIAOZHI, age=25.0, address=山西太原}, map11={id=1, name=QIAOZHI, age=25.0, address=山西太原}}, {21={id=11, name=QIAOZHI, age=25.0, address=山西太原}, 22={id=21, name=QIAOZHI, age=25.0, address=山西太原}}]
        System.out.println(list.get(1));
//        {21={id=11, name=QIAOZHI, age=25.0, address=山西太原}, 22={id=21, name=QIAOZHI, age=25.0, address=山西太原}}
    }
}

注意:

json转普通的Javabean只需要两个简单的参数，第一个是json字符串，第二个是需要转换对象的类型。  

User user = gson.fromJson(json, User.class);

json转集合与map类型需要使用了TypeToken，它是gson提供的数据类型转换器，可以支持各种数据集合类型转换。也就是通知GSON将json转为那种集合

list = (List<User>) gson.fromJson(json, new TypeToken<List<User>>(){}.getType());

map = (Map<String,User>) gson.fromJson(json, new TypeToken<Map<String,User>>(){}.getType());

list = gson.fromJson(json, new TypeToken<List<Map<String,User>>>(){}.getType());

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原文地址：https://www.cnblogs.com/qlqwjy/p/7270627.html