Gson入门示例

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Gson is a Java library that can be used to convert Java Objects into their JSON representation. It can also be used to convert a JSON string to an equivalent Java object.

本文主要涉及如下内容：

1、JSON 字符串转对象；
2、JSON 字符串转集合；
3、对象转 JSON 字符串；

App.java

package demo.gson;

import com.google.gson.Gson;
import com.google.gson.reflect.TypeToken;
import demo.gson.entity.User;

import java.util.ArrayList;
import java.util.List;

public class App {public static void main(String[] args) {App.testConvertObjectToJson();
        App.testConvertListToJson();
        App.testConvertJsonToObject();
        App.testConvertJsonToList();}

    private static void testConvertObjectToJson() {System.out.println("== testConvertObjectToJson ==");
        User user = new User("1", "0001", "程序员", "111", "test@qq.com");
        System.out.println(new Gson().toJson(user));
        // 结果：{"id":"1","usercode":"0001","username":"程序员","password":"111","email":"test@qq.com"}
    }

    private static void testConvertListToJson() {System.out.println("== testConvertListToJson ==");
        List<User> list = new ArrayList<>();
        list.add(new User("1", "0001", "程序员 1", "111", "test1@qq.com"));
        list.add(new User("2", "0002", "程序员 2", "222", "test2@qq.com"));
        System.out.println(new Gson().toJson(list));
        // 结果：[{"id":"1","usercode":"0001","username":"程序员 1","password":"111","email":"test1@qq.com"},{"id":"2","usercode":"0002","username":"程序员 2","password":"222","email":"test2@qq.com"}]
    }

    private static void testConvertJsonToObject() {System.out.println("== testConvertJsonToObject ==");
        String json = "{\"id\":\"1\",\"usercode\":\"0001\",\"username\":\" 程序员 \",\"password\":\"111\",\"email\":\"test@qq.com\"}";
        System.out.println(new Gson().fromJson(json, User.class));
        /*
        结果：User[id='1', usercode='0001', username='程序员', password='111', email='test@qq.com', createTime=null]
         */
    }

    private static void testConvertJsonToList() {System.out.println("== testConvertJsonToList ==");
        String json = "[{\"id\":\"1\",\"usercode\":\"0001\",\"username\":\" 程序员 1\",\"password\":\"111\",\"email\":\"test1@qq.com\"},{\"id\":\"2\",\"usercode\":\"0002\",\"username\":\" 程序员 2\",\"password\":\"222\",\"email\":\"test2@qq.com\"}]";
        List<User> list = new Gson().fromJson(json, new TypeToken<List<User>>(){}.getType());
        list.forEach(user -> System.out.println(user));
        /*
        结果：User[id='1', usercode='0001', username='程序员 1', password='111', email='test1@qq.com', createTime=null]
        User[id='2', usercode='0002', username='程序员 2', password='222', email='test2@qq.com', createTime=null]
         */
    }
}

User.java

package demo.gson.entity;

import java.util.Date;
import java.util.StringJoiner;

/**
 * @Description: 用户
 */
public class User {

    /**
     * 主键
     */
    private String id;
    /**
     * 用户编码
     */
    private String usercode;
    /**
     * 用户名称
     */
    private String username;
    /**
     * 密码
     */
    private String password;
    /**
     * 邮箱
     */
    private String email;
    /**
     * 创建时间
     */
    private Date createTime;

    public User() {}

    public User(String id, String usercode, String username, String password, String email) {
        this.id = id;
        this.usercode = usercode;
        this.username = username;
        this.password = password;
        this.email = email;
    }

    public String getId() {return id;}

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

    public String getUsercode() {return usercode;}

    public void setUsercode(String usercode) {this.usercode = usercode;}

    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;}

    public String getEmail() {return email;}

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

    public Date getCreateTime() {return createTime;}

    public void setCreateTime(Date createTime) {this.createTime = createTime;}

    @Override
    public String toString() {return new StringJoiner(",", User.class.getSimpleName() + "[", "]")
                .add("id='" + id + "'")
                .add("usercode='" + usercode + "'")
                .add("username='" + username + "'")
                .add("password='" + password + "'")
                .add("email='" + email + "'")
                .add("createTime=" + createTime)
                .toString();}
}