JSONObject、 JsonObject、阿里fastJson、谷歌gson区别

JSON：JavaScript Object Notation Java对象表示法

Java中并没有内置的 JSON 解析，需要使用第三方类库。常用的类库如下

一、Gson ： 古河开发的JSON 库

二、FastJson ：阿里巴巴的JSON 库

三、JackSon ： 社区十分活跃

JSONObject 是json 对象，一个键对应一个值，例如： {“key”:"value"}

一、com.alibaba.fastjson.JsonObject（参考）

1.添加fastJson依赖

 <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>fastjson</artifactId>
            <version>1.2.58</version>
</dependency>

2.将 List 对象转换为 Json 格式的String

 List<User> users= findAllUser();

 String str = JSONObject.toJSONString(users);

3.将 Map 对象转换为 JsonObject

 Map<String,Object> map = new HashMap();
        map.put("name","zhangsan");
        map.put("age","15");
JSONObject jsonObject = new JSONObject(map);

4.将Map 转换为 Json 格式的String 字符串

  String jsonStr = JSON.toJSONString(map);

5.将 json 格式的String 字符串转换为 Map 

 String jsonStr = "{\"name\":\"zhangsan\",\"age\":\"15\"}";

 JSONObject  jsonObject = JSONObject.parseObject(jsonStr);

 Map<String,Object> map = jsonObject;

6. 将 json 格式的字符串转换为 JsonObject

String jsonStr = "{\"name\":\"zhangsan\",\"age\":\"15\"}";

JSONObject jsonObject = JSON.parseObject(jsonStr);

7. 将 json字符串转换为 Java对象

 String jsonStr = "{\"name\":\"zhangsan\",\"email\":\"15\"}";

 User user = JSON.parseObject(jsonStr,User.class);

8. 将 json 字符串转换为 JSONArray 数组

 String jsonStr = "[{\"name\":\"zhangsan\",\"email\":\"zhangsan@qq.com\"},{\"name\":\"lisi\",\"email\":\"lisi@163.com\"}]";

        JSONArray array = JSON.parseArray(jsonStr);

        for(int i=0;i<array.size();i++){
            System.out.println(array.get(i));
        }

9. 将Java 对象转换为 json 字符串

 User user = new User(11,"wangwu","wangwu@163.com","上海");

 String str = JSON.toJSONString(user);

10. 将json 字符串转换为 Java 实体集合

 String jsonStr = "[{\"name\":\"zhangsan\",\"email\":\"zhangsan@qq.com\"},{\"name\":\"lisi\",\"email\":\"lisi@163.com\"}]";
 List<User> list = JSON.parseArray(jsonStr,User.class);

11. 将 java 对象转换为 JsonObject

  User user = new User(11,"wangwu","wangwu@163.com","上海");

  JSONObject jsonObject = (JSONObject) JSON.toJSON(user);

二、org.json.JSONObject

1.添加依赖

　<dependency>
            <groupId>org.json</groupId>
            <artifactId>json</artifactId>
            <version>20180130</version>
 </dependency>

2.Bean 对象转换为 JSONObject

User user = new User(11,"wangwu","wangwu@163.com","上海");

JSONObject jsonObject = new JSONObject(user);

3.Map 集合转换为 JSONObject 对象

  Map<String,Object> map = new HashMap();
        map.put("name","zhangsan");
        map.put("age","15");

  JSONObject jsonObject = new JSONObject(map);

4.JSONObject 转换为 Map<String,Object>对象

    JSONObject jsonObject = new JSONObject();
    jsonObject.toMap();

三、GSON（参考）

1.添加依赖

  <dependency>
     <groupId>com.google.code.gson</groupId>
     <artifactId>gson</artifactId>
     <version>2.3.1</version>
  </dependency>

2.Gson 的两个基础方法

toJson();
fromJson();

3.创建方式一：

// 使用new方法
Gson gson = new Gson();

// toJson 将bean对象转换为json字符串
String jsonStr = gson.toJson(user, User.class);

// fromJson 将json字符串转为bean对象
Student user= gson.fromJson(jsonStr, User.class);

// **序列化List**
String jsonStr2 = gson.toJson(list);

// **反序列化成List时需要使用到TypeToken getType()**
List<User> retList = gson.fromJson(jsonStr2,new TypeToken<List<User>>(){}.getType());

创建方式二：

//serializeNulls()是GsonBuilder提供的一种配置，当字段值为空或null时，依然对该字段进行转换
Gson gson = new GsonBuilder().serializeNulls().create(); 

使用GsonBuilder创建Gson实例的步骤：

首先创建GsonBuilder,然后调用GsonBuilder提供的各种配置方法进行配置，最后调用GsonBuilder的create方法，将基于当前的配置创建一个Gson实例。

附录00：

 package entity;

 /**
  * Created by baizhuang on 2019/9/23 16:29.
  */

 public class User {
     private int id;
     private String name;
     private String email;
     private String address;

     public User() {
     }

     public User(int id, String name, String email, String address) {
         this.id = id;
         this.name = name;
         this.email = email;
         this.address = address;
     }

     @Override
     public String toString() {
         return "User{" +
                 "id=" + id +
                 ", name='" + name + '\'' +
                 ", email='" + email + '\'' +
                 ", address='" + address + '\'' +
                 '}';
     }

     public int getId() {
         return id;
     }

     public void setId(int id) {
         this.id = id;
     }

     public String getName() {
         return name;
     }

     public void setName(String name) {
         this.name = name;
     }

     public String getEmail() {
         return email;
     }

     public void setEmail(String email) {
         this.email = email;
     }

     public String getAddress() {
         return address;
     }

     public void setAddress(String address) {
         this.address = address;
     }
 }

附录01：

 package entity;

 import com.alibaba.fastjson.JSON;
 import com.alibaba.fastjson.JSONArray;
 import com.alibaba.fastjson.JSONObject;
 import java.util.Arrays;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;

 /**
  * Created by baizhuang on 2019/9/23 16:30.
  */

 public class Test {

     public static List<User> findAllUser(){
         return  Arrays.asList(
                 new User(1,"zhangsan","zhang","北京"),
                 new User(2,"lisi","li","上海"));

     }

     public static void listToJsonString(){
         List<User> users= findAllUser();

         System.out.println(users);

         String str = JSONObject.toJSONString(users);

         System.out.println(str);
     }

     public static  void maptoJsonObject(){
         Map<String,Object> map = new HashMap();
         map.put("name","zhangsan");
         map.put("age","15");
         JSONObject jsonObject = new JSONObject(map);
         System.out.printf("Json:"+jsonObject);

         String jsonStr = JSON.toJSONString(map);
         System.out.println(jsonStr);

     }

     public static void stringToMap(){

         String jsonStr = "{\"name\":\"zhangsan\",\"age\":\"15\"}";

         JSONObject  jsonObject = JSONObject.parseObject(jsonStr);

         Map<String,Object> map = jsonObject;

     }

     public static  void jsonToJsonObject(){
         String jsonStr = "{\"name\":\"zhangsan\",\"age\":\"15\"}";

         JSONObject jsonObject = JSON.parseObject(jsonStr);

         System.out.println(jsonObject);
     }

     public static void jsonStrToJsonBean(){
         String jsonStr = "{\"name\":\"zhangsan\",\"email\":\"15\"}";

         User user = JSON.parseObject(jsonStr,User.class);

         System.out.println(user);
     }

     public static void jsonStrToJsonArray(){
         String jsonStr = "[{\"name\":\"zhangsan\",\"email\":\"zhangsan@qq.com\"},{\"name\":\"lisi\",\"email\":\"lisi@163.com\"}]";

         JSONArray array = JSON.parseArray(jsonStr);

         for(int i=0;i<array.size();i++){
             System.out.println(array.get(i));
         }
     }

     public static void javaBeanToJsonStr(){
         User user = new User(11,"wangwu","wangwu@163.com","上海");

         String str = JSON.toJSONString(user);
         System.out.println(str);
     }

     public static void jsonStrToBeanList(){
         String jsonStr = "[{\"name\":\"zhangsan\",\"email\":\"zhangsan@qq.com\"},{\"name\":\"lisi\",\"email\":\"lisi@163.com\"}]";
         List<User> list = JSON.parseArray(jsonStr,User.class);
         for(User user : list){
             System.out.println(user);
         }
     }

     public static void beanToJsonObject(){
         User user = new User(11,"wangwu","wangwu@163.com","上海");

         JSONObject jsonObject = (JSONObject) JSON.toJSON(user);

         System.out.println(jsonObject);

     }

     public static void main(String []args){
         //listToJsonString();
         //();
        // stringToMap();
        // jsonToJsonObject();
        // jsonStrToJsonBean();
         //jsonStrToJsonArray();
        // javaBeanToJsonStr();
         //jsonStrToBeanList();
         beanToJsonObject();

     }
 }

附录02：

 public class TestOrgJson {

     public static void beanToJSONObject(){
         User user = new User(11,"wangwu","wangwu@163.com","上海");

         JSONObject jsonObject = new JSONObject(user);

         System.out.println(jsonObject);
     }

     public static void mapToJSONObject(){

         Map<String,Object> map = new HashMap();
         map.put("name","zhangsan");
         map.put("age","15");

         JSONObject jsonObject = new JSONObject();
         jsonObject.toMap();
     }

     public static void main(String []args){

     }
 }