JavaWeb22.3【Ajax&Json：JSON数据和Java对象的相互转换】

 

 

 

 

package com.haifei.domain;

import com.fasterxml.jackson.annotation.JsonFormat;
import com.fasterxml.jackson.annotation.JsonIgnore;

import java.util.Date;

public class Person {

    private String name;
    private int age;
    private String gender;

//    @JsonIgnore
    @JsonFormat(pattern = "yyyy-MM-dd")
    private Date birthday;

    public Person() {
    }

    public Person(String name, int age, String gender) {
        this.name = name;
        this.age = age;
        this.gender = gender;
    }

    public Person(String name, int age, String gender, Date birthday) {
        this.name = name;
        this.age = age;
        this.gender = gender;
        this.birthday = birthday;
    }

    public Date getBirthday() {
        return birthday;
    }

    public void setBirthday(Date birthday) {
        this.birthday = birthday;
    }

    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 getGender() {
        return gender;
    }

    public void setGender(String gender) {
        this.gender = gender;
    }

    @Override
    public String toString() {
        return "Person{" +
                "name='" + name + '\'' +
                ", age=" + age +
                ", gender='" + gender + '\'' +
                '}';
    }
}

package com.haifei.test;

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.haifei.domain.Person;
import org.junit.Test;

import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
import java.util.*;

public class JacksonTest {

    //java对象转为json字符串
    @Test
    public void test1() throws Exception {
        //1 创建java对象
        Person p = new Person("张三", 23, "男");

        //2  创建Jackson核心对象 ObjectMapper
        ObjectMapper om = new ObjectMapper();

        //3 调用ObjectMapper的相关方法进行转换
        /*
            转换方法：
                writeValue(参数1，obj):
                    参数1：
                        File：将obj对象转换为JSON字符串，并保存到指定的文件中
                        Writer：将obj对象转换为JSON字符串，并将json数据填充到字符输出流中
                        OutputStream：将obj对象转换为JSON字符串，并将json数据填充到字节输出流中
                writeValueAsString(obj):将对象转为json字符串
        */
        String jsonStr = om.writeValueAsString(p);
        System.out.println(jsonStr); //{"name":"张三","age":23,"gender":"男"}

        om.writeValue(new File("./a.txt"), p); //day22模块目录下，与src同级
        om.writeValue(new FileWriter("./b.txt"), p);
    }


    //特殊：日期类型
    @Test
    public void test2() throws Exception {
        Person p = new Person("张三", 23, "男", new Date());
        ObjectMapper mapper = new ObjectMapper();
        String json = mapper.writeValueAsString(p);
        System.out.println(json);
        /*
        默认情况下
            {"name":"张三","age":23,"gender":"男","birthday":1625740824782}
            java对象的日期属性被转为json时，默认为毫秒值

         在javabean中对日期属性进行注解，可以优化
             （1）@JsonIgnore：排除属性
                {"name":"张三","age":23,"gender":"男"}
             （2）@JsonFormat：属性值的格式化
                {"name":"张三","age":23,"gender":"男","birthday":"2021-07-08"}
         */
    }


    //list集合转为json字符串
    @Test
    public void test3() throws Exception {
        Person p1 = new Person("张三", 23, "男", new Date());
        Person p2 = new Person("李四", 22, "女", new Date());
        Person p3 = new Person("王五", 21, "男", new Date());

        List<Person> ps = new ArrayList<>();
        ps.add(p1);
        ps.add(p2);
        ps.add(p3);

        ObjectMapper mapper = new ObjectMapper();
        String json = mapper.writeValueAsString(ps);
        System.out.println(json); //[{"name":"张三","age":23,"gender":"男","birthday":"2021-07-08"},{"name":"李四","age":22,"gender":"女","birthday":"2021-07-08"},{"name":"王五","age":21,"gender":"男","birthday":"2021-07-08"}]
        //数组格式
    }


    //map集合转为json字符串
    @Test
    public void test4() throws Exception {
        Map<String, Object> map = new HashMap<>();
        map.put("name", "张三");
        map.put("age", "23");
        map.put("gender", "男");

        ObjectMapper mapper = new ObjectMapper();
        String json = mapper.writeValueAsString(map);
        System.out.println(json); //{"gender":"男","name":"张三","age":"23"}
    }


    //JSON转为Java对象
    @Test
    public void test5() throws Exception {
        //1 初始化json字符串
        String jsonStr = "{\"gender\":\"男\",\"name\":\"张三\",\"age\":\"23\"}";

        //2 创建ObjectMapper
        ObjectMapper mapper = new ObjectMapper();

        //3 转换为java对象
        Person person = mapper.readValue(jsonStr, Person.class);
        System.out.println(person); //Person{name='张三', age=23, gender='男'}
    }
}

?

1 2	a.txt = b.txt {"name":"张三","age":23,"gender":"男"}