GSON入门篇（内含教学视频+源代码）

教学视频+源代码下载链接地址：https://download.csdn.net/download/weixin_46411355/87474475

目录

• GSON入门篇（内含教学视频+源代码）
• `教学视频+源代码下载链接地址：`[https://download.csdn.net/download/weixin_46411355/87474475](https://download.csdn.net/download/weixin_46411355/87474475)
• • 一、创建一个JavaSE项目
  • 二、IDEA中导入gson的jar包
  • 三、创建JavaBean
  • 四、测试类
  • • 4.1 一个对象转JSON
    • 4.2 多个对象转JSON
    • 4.3 JSON字符串转一个对象
    • 4.4 JSON字符串转多个对象（List）
    • • 4.4.1 错误案例
      • 4.4.2 正确案例

一、创建一个JavaSE项目

二、IDEA中导入gson的jar包

笔者的gson jar包的下载连接地址：https://download.csdn.net/download/weixin_46411355/87474404

复习：IDEA导入第三方jar包的方式。可以查看笔者的另一篇博文《IDEA导入和删除第三方jar包》——https://huanghaoheng.blog.csdn.net/article/details/126332558

创建一个lib目录，并将下载好的jar包放进lib目录中

点击File->Project Structure

点击Modules
点击你的项目或Module
点击Dependencies
点击“+”
点击“1 JARs or directories”

选择你jar包所在的路径，然后点击ok

再点击ok

同时再导入lombok和Junit的jar包，步骤一样，此处省略
笔者的lombok jar包下载链接地址：https://download.csdn.net/download/weixin_46411355/87474401
笔者的Junit jar包下载链接地址：https://download.csdn.net/download/weixin_46411355/87398726

三、创建JavaBean

User.java

package com.bjpowernode.domain;

import com.oracle.webservices.internal.api.databinding.DatabindingMode;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
import lombok.ToString;

@ToString
@AllArgsConstructor
@NoArgsConstructor
@Data
public class User {
    private Integer id;
    private String username;
    private String password;
    private String nickname;
    private Integer age;
}

四、测试类

4.1 一个对象转JSON

 /**
     * 测试一个对象转JSON
     */
    @Test
    public void testOneObjectConvertToJSON(){
        User user = new User(1,"zhangsan","123456","三丰大师",149) ;
        Gson gson = new Gson();
        //写法一
        System.out.println("=======================写法一=========================");
        String userJson = gson.toJson(user, User.class);
        System.out.println("userJson = " + userJson);//userJson = {"id":1,"username":"zhangsan","password":"123456","nickname":"三丰大师","age":149}

        //写法二
        System.out.println("========================写法二=========================");
        String userJson2 = gson.toJson(user);
        System.out.println("userJson2 = " + userJson2);
    }

4.2 多个对象转JSON

/**
     * 测试多个对象转JSON
     */
    @Test
    public void testManyObjectConvertToJSON(){
        List<User> users = new ArrayList<>();
        User user = null;
        for (int i = 1; i <=5 ; i++) {
             user = new User(i,"hhh"+i,123456+"i","哈哈哈"+i,24+i);
            users.add(user);
        }
        Gson gson  = new Gson();
        String usersJson = gson.toJson(users);
        System.out.println("usersJson = " + usersJson);
    }

4.3 JSON字符串转一个对象

 /**
     * 测试JSON字符串转一个对象
     */
    @Test
    public void testJSONSConvertToOneObject(){
        //如何将JSON字符串转换成对象
        String jsonStr = "{\"id\":1,\"username\":\"zhangsan\",\"password\":\"123456\",\"nickname\":\"三丰大师\",\"age\":149}";
        Gson gson = new Gson();
        User user = gson.fromJson(jsonStr, User.class);
        System.out.println("user = " + user);
    }

4.4 JSON字符串转多个对象（List）

4.4.1 错误案例

 /**
     * 测试JSON字符串转多个对象（List）（错误案例）
     */
    @Test
    public void testJSONConvertManyObjectErrorInstance(){
        String jsonStr = "[{\"id\":1,\"username\":\"hhh1\",\"password\":\"123456i\",\"nickname\":\"哈哈哈1\",\"age\":25},{\"id\":2,\"username\":\"hhh2\",\"password\":\"123456i\",\"nickname\":\"哈哈哈2\",\"age\":26},{\"id\":3,\"username\":\"hhh3\",\"password\":\"123456i\",\"nickname\":\"哈哈哈3\",\"age\":27},{\"id\":4,\"username\":\"hhh4\",\"password\":\"123456i\",\"nickname\":\"哈哈哈4\",\"age\":28},{\"id\":5,\"username\":\"hhh5\",\"password\":\"123456i\",\"nickname\":\"哈哈哈5\",\"age\":29}]\n";
        Gson gson = new Gson();

        ArrayList<User> arrayList = gson.fromJson(jsonStr, ArrayList.class);
        /*上面这行代码，使得结果输出如下：
        *   {id=1.0, username=hhh1, password=123456i, nickname=哈哈哈1, age=25.0}
            {id=2.0, username=hhh2, password=123456i, nickname=哈哈哈2, age=26.0}
            {id=3.0, username=hhh3, password=123456i, nickname=哈哈哈3, age=27.0}
            {id=4.0, username=hhh4, password=123456i, nickname=哈哈哈4, age=28.0}
            {id=5.0, username=hhh5, password=123456i, nickname=哈哈哈5, age=29.0}
            输出的结果，既不是对象，也不是JSON字符串
            对象 ：User(id=1, username=zhangsan, password=123456, nickname=三丰大师, age=149)
            JSON字符串 : {"id":1,"username":"zhangsan","password":"123456","nickname":"三丰大师","age":149}
        */

//        for (Object o : arrayList) {
//            System.out.println(o);
//        }
        arrayList.forEach(System.out::println);

    }

4.4.2 正确案例

@Test
    public void testJSONConvertManyObjectCorrectInstance(){
        String jsonStr = "[{\"id\":1,\"username\":\"hhh1\",\"password\":\"123456i\",\"nickname\":\"哈哈哈1\",\"age\":25},{\"id\":2,\"username\":\"hhh2\",\"password\":\"123456i\",\"nickname\":\"哈哈哈2\",\"age\":26},{\"id\":3,\"username\":\"hhh3\",\"password\":\"123456i\",\"nickname\":\"哈哈哈3\",\"age\":27},{\"id\":4,\"username\":\"hhh4\",\"password\":\"123456i\",\"nickname\":\"哈哈哈4\",\"age\":28},{\"id\":5,\"username\":\"hhh5\",\"password\":\"123456i\",\"nickname\":\"哈哈哈5\",\"age\":29}]\n";
        Gson gson = new Gson();

        Type type = new TypeToken<ArrayList<User>>(){}.getType();

        ArrayList<User> arrayList = gson.fromJson(jsonStr, type);

//        for (User user : arrayList) {
//            System.out.println(user);
//        }
        arrayList.forEach(System.out::println);
        /*  输出结果如下
        *   User(id=1, username=hhh1, password=123456i, nickname=哈哈哈1, age=25)
            User(id=2, username=hhh2, password=123456i, nickname=哈哈哈2, age=26)
            User(id=3, username=hhh3, password=123456i, nickname=哈哈哈3, age=27)
            User(id=4, username=hhh4, password=123456i, nickname=哈哈哈4, age=28)
            User(id=5, username=hhh5, password=123456i, nickname=哈哈哈5, age=29)
        *
        */
    }