jsonJackson的使用

Posted 2020-11-01 胖子学习天地

Jackson所有的操作都是通过ObjectMapper对象实例来操作的，可以重用这个对象实例。

首先定义一个实例：
ObjectMapper mapper = new ObjectMapper();

定义一个Student类:

    package jackson;

    import java.util.Date;

    public class Student {

        private String name;
        private int age;
        private String position;
        private Date createTime;

        public String getName() {
            return name;
        }

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

        public int getAge() {
            return age;
        }

        public void setAge(int age) {
            this.age = age;
        }

        public String getPosition() {
            return position;
        }

        public void setPosition(String position) {
            this.position = position;
        }

        public Date getCreateTime() {
            return createTime;
        }

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

        @Override
        public String toString() {
            return "Student [name=" + name + ", age=" + age + ", position="
                    + position + ", createTime=" + createTime + "]";
        }

    }

准备一个字符串：
String jsonString = "{\"name\":\"king\",\"age\":21}";

常规操作: 字符串转对象

     mapper.readValue(jsonString,Student.class);
     System.out.println(student);

打印输出结果：

Student [name=king, age=21, position=null, createTime=null]

常规操作: 对象转字符串

        student.setCreateTime(new Date());
        String json = mapper.writeValueAsString(student);
        System.out.println(json);

打印输出结果：

{"name":"king","age":21,"position":null,"createTime":1524819355361}

如何改变输出的日期字段格式?

两种方式：一种SimpleDateFormat，另外一种通过在属性字段注解
在Student.java属性字段createTime注解@JsonFormat(pattern = "yyyy-MM-dd HH:mm:ss")

import com.fasterxml.jackson.annotation.JsonFormat;

public class Student {

    private String name;
    private int age;
    private String position;
    @JsonFormat(pattern = "yyyy-MM-dd HH:mm:ss")  
    private Date createTime;
      
       //省略get,set
}

打印输出结果：

{"name":"king","age":21,"position":null,"createTime":"2018-04-27 09:00:56"}

8小时时间差问题：上面打印结果发现，时间少8小时。

解决方法: 注解上增加时区。

public class Student {

    private String name;
    private int age;
    private String position;
    @JsonFormat(pattern = "yyyy-MM-dd HH:mm:ss", timezone = "GMT+8")  
    private Date createTime;
        
        //省略get,set
}

打印输出结果：

{"name":"king","age":21,"position":null,"createTime":"2018-04-27 17:07:33"}