Java操作json

Java操作json的库

库很多,这里以fastjson为例

<dependency>
    <groupId>com.alibaba</groupId>
    <artifactId>fastjson</artifactId>
    <version>1.2.76</version>
</dependency>

Hutool 一个小而全的工具库

Hutool API

<dependency>
    <groupId>cn.hutool</groupId>
    <artifactId>hutool-all</artifactId>
    <version>5.8.4</version>
</dependency>

java操作json 实操 序列化

package com.sheep.emo.pojo;

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

/**
 * @Description : Person实体类
 * @Author : sheep669
 * @Created at 2022/7/8 22:13
 */

@Data
@NoArgsConstructor
@AllArgsConstructor
public class Person {
    private Integer userId;
    private String userName;
    private String pwd;
    private String location;
    private Character sex;

}

package com.sheep.emo;

import cn.hutool.core.util.StrUtil;
import com.alibaba.fastjson.JSON;
import com.sheep.emo.pojo.Person;
import org.junit.jupiter.api.Test;
import org.springframework.boot.test.context.SpringBootTest;

@SpringBootTest
class EmoApplicationTests {

    @Test
    void contextLoads() {
        Person person = new Person();
        person.setUserId(12);
        person.setUserName("张三");
        person.setSex('男');
        person.setPwd("23242");
        person.setLocation("北京市公安局");
        String s = JSON.toJSONString(person);
        System.out.println(s);
        // StrUtil.toUnderlineCase(s) 驼峰转下划线
        String s1 = StrUtil.toUnderlineCase(s);
        System.out.println(s1);
    }

}

{"location":"北京市公安局","pwd":"23242","sex":"男","userId":12,"userName":"张三"}
{"location":"北京市公安局","pwd":"23242","sex":"男","user_id":12,"user_name":"张三"}

Process finished with exit code 0

允许字段为空

// SerializerFeature.WriteMapNullValue 允许字段为空
String s = JSON.toJSONString(person, SerializerFeature.WriteMapNullValue);
System.out.println(s);

console

{"location":"北京市公安局","pwd":"23242","sex":"男","userId":12,"userName":null}

处理时间格式

// 实体类加上注解
@JSONField(format = "yyyy-MM-dd HH:mm:ss")
private LocalDateTime birthday;
@JSONField(format = "yyyy-MM-dd HH:mm:ss")
private Date createTime;

原来：

{"birthday":"2022-07-08T22:59:16.604","createTime":1657292356604}
{"birthday":"2022-07-08T22:59:16.604","create_time":1657292356604}

现在：

{"birthday":"2022-07-08 23:00:24","createTime":"2022-07-08 23:00:24"}
{"birthday":"2022-07-08 23:00:24","create_time":"2022-07-08 23:00:24"}

集合序列化后面出现 $ref 引用探测

 @Test
    public void test$Ref() {
        List<Person> list = new ArrayList<>();
        Person person = new Person();
        person.setUserName("张三");
        person.setPwd("23242");
        person.setLocation("北京市公安局");
        list.add(person);
        list.add(person);
        list.add(person);
        String s = JSON.toJSONString(list);
        System.out.println(s);
}

console

[{"location":"北京市公安局","pwd":"23242","userName":"张三"},{"$ref":"$[0]"},{"$ref":"$[0]"}]

// SerializerFeature.DisableCircularReferenceDetect 禁用引用探测功能
String s = JSON.toJSONString(list, SerializerFeature.DisableCircularReferenceDetect);
System.out.println(s);

console

[{"location":"北京市公安局","pwd":"23242","userName":"张三"},{"location":"北京市公安局","pwd":"23242","userName":"张三"},{"location":"北京市公安局","pwd":"23242","userName":"张三"}]

序列化定制处理 以key转大写为例

    @Test
    public void testSerializeFilter() {
        Person person = new Person();
        person.setUserId(1);
        person.setUserName("张三");
        person.setSex('男');
        person.setLocation("北京市公安局");

        //指定输出json的key大写
        //Object var1:对象 String var2:属性 Object var3：值
        NameFilter nameFilter = (object, key, value) -> {
            // 进行处理
            return key.toUpperCase();
        };

        String s = JSON.toJSONString(person, nameFilter);
        System.out.println(s);
    }

console

{"LOCATION":"北京市公安局","SEX":"男","USERID":1,"USERNAME":"张三"}

命名补全，自定义 @JSONField(name = "xxxx")

原来：

{"pwd":"23242"}

@JSONField(name = "password")
private String pwd;

现在：

{"password":"23242"}

美化输出 一般不用

    @Test
    void contextLoads() {
        Person person = new Person();
        person.setUserId(12);
        // person.setUserName("张三");
        person.setSex('男');
        person.setPwd("23242");
        person.setLocation("北京市公安局");
        person.setBirthday(LocalDateTime.now());
        person.setCreateTime(new Date());
        // SerializerFeature.WriteMapNullValue 允许字段为空 SerializerFeature.PrettyFormat 美化输出
        String s = JSON.toJSONString(person, SerializerFeature.WriteMapNullValue, SerializerFeature.PrettyFormat);
        System.out.println(s);
        String s1 = StrUtil.toUnderlineCase(s);
        System.out.println(s1);
    }

console

{
	"birthday":"2022-07-09 00:04:11",
	"createTime":"2022-07-09 00:04:11",
	"location":"北京市公安局",
	"pwd":"23242",
	"sex":"男",
	"userId":12,
	"userName":null
}
{
	"birthday":"2022-07-09 00:04:11",
	"create_time":"2022-07-09 00:04:11",
	"location":"北京市公安局",
	"pwd":"23242",
	"sex":"男",
	"user_id":12,
	"user_name":null
}

java操作json 实操 反序列化

    @Test
    public void test() {
        String jsonString = "{\"birthday\":\"2022-07-08 23:30:29\",\"create_time\":\"2022-07-08 23:30:29\",\"location\":\"北京市公安局\",\"pwd\":\"23242\",\"sex\":\"男\",\"user_id\":12,\"user_name\":null}";
        //反序列化 JSON.parseObject()
        Person person = JSON.parseObject(jsonString, Person.class);
        System.out.println(person);
    }

console

Person(userId=12, userName=null, pwd=23242, location=北京市公安局, sex=男, birthday=2022-07-08T23:30:29, createTime=Fri Jul 08 23:30:29 CST 2022)

package com.sheep.emo.pojo;

import lombok.Data;

/**
 * @Description : TODO
 * @Author : sheep669
 * @Created at 2022/7/8 23:35
 */
@Data
public class ResultVO<T> {
    private Boolean success;
    private T data;

    private ResultVO() {
    }

    public static <T> ResultVO<T> buildSuccess(T t) {
        ResultVO<T> resultVO = new ResultVO<>();
        resultVO.setData(t);
        return  resultVO;
    }

}

    @Test
    public void test() {
        String jsonString2 = "{\"data\":{\"birthday\":\"2022-07-08 23:30:29\",\"createTime\":\"2022-07-08 23:30:29\",\"location\":\"北京市公安局\",\"pwd\":\"23242\",\"sex\":\"男\",\"userId\":12}}";
        // 反序列化不能获取到泛型 需要强制类型转换
        ResultVO resultVO = JSON.parseObject(jsonString2, ResultVO.class);
        Object data1 = resultVO.getData();
        Person person1 =(Person) resultVO.getData();
        System.out.println(person1.getUserName());
        System.out.println((Person)data1);
        
        // new TypeReference<ResultVO<Person>>() {} 需要什么类型传什么，这里是ResultVO<Person>
        ResultVO<Person> personResultVO1 = JSON.parseObject(jsonString2, new TypeReference<ResultVO<Person>>() {});
        // 直接就拿到了Person对象
        Person person2 = personResultVO1.getData();
        System.out.println(person2.getUserName());
    }

指定某个字段不参与序列化 @JSONField(serialize = false, deserialize = false)

// 不参与序列化和反序列化 serialize = false, deserialize = false
@JSONField(serialize = false, deserialize = false)
private String pwd;