JSON数据和Java对象的相互转换

package 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 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 + '\'' +
                ", birthday=" + birthday +
                '}';
    }
}

package test;

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

import java.util.*;

public class JacksonTest {
    //测试java对象转换成json字符串
    @Test
    public void test1() throws Exception {
        //1.创建person对象
        Person p=new Person();
        p.setName("张三");
        p.setAge(23);
        p.setGender("男");
        //2.创建核心对象objectmapper
        ObjectMapper mapper=new ObjectMapper();
        //3.调用方法
        /*  3.1. 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*/
        //使用writeValueAsString方法并打印字符串
        String s = mapper.writeValueAsString(p);
//        System.out.println(s);//{"name":"张三","age":23,"gender":"男"}
        //使用writeValue方法将p对象写入到d:\\a.txt文件中
//        mapper.writeValue(new File("d:\\a.txt"),p);
        //使用writeValue方法将p对象写入到d:\\b.txt文件输出流中
//        mapper.writeValue(new FileWriter("d:/b.txt"),p);
    }

    @Test
    //测试注解
    public void test2() throws Exception {
        //1.创建person对象
        Person p = new Person();
        p.setName("张三");
        p.setAge(23);
        p.setGender("男");
        p.setBirthday(new Date());
        //2.创建核心对象objectmapper
        ObjectMapper mapper = new ObjectMapper();
        //3.调用方法
        String s = mapper.writeValueAsString(p);
        System.out.println(s);//{"name":"张三","age":23,"gender":"男","birthday":"2020-02-04"}
    }

    @Test
    //测试list集合
    public void test3() throws Exception {
        //1.创建person对象
        Person p = new Person();
        p.setName("张三");
        p.setAge(23);
        p.setGender("男");
        p.setBirthday(new Date());
        Person p1 = new Person();
        p1.setName("李四");
        p1.setAge(24);
        p1.setGender("男");
        p1.setBirthday(new Date());
        Person p2 = new Person();
        p2.setName("王五");
        p2.setAge(25);
        p2.setGender("女");
        p2.setBirthday(new Date());
        ArrayList list=new ArrayList();
        list.add(p);
        list.add(p1);
        list.add(p2);
        //2.创建核心对象objectmapper
        ObjectMapper mapper = new ObjectMapper();
        //3.调用方法
        String s = mapper.writeValueAsString(list);
        System.out.println(s);//打印出来是数组的形式[{},{},{}]
        //[{"name":"张三","age":23,"gender":"男","birthday":"2020-02-04"},
        // {"name":"李四","age":24,"gender":"男","birthday":"2020-02-04"},
        // {"name":"王五","age":25,"gender":"女","birthday":"2020-02-04"}]
    }

    @Test
    //测试map集合
    public void test4() throws Exception {
        Map<String,Object> map=new HashMap<String,Object>();
        map.put("name","张三");
        map.put("age",23);
        map.put("gender","男");
        //2.创建核心对象objectmapper
        ObjectMapper mapper = new ObjectMapper();
        //3.调用方法
        String s = mapper.writeValueAsString(map);
        System.out.println(s);//{"gender":"男","name":"张三","age":23}
    }

    @Test
    //测试json转换成java对象
    public void test5() throws Exception {
        //1.创建json字符串对象
        String json="{\"gender\":\"男\",\"name\":\"张三\",\"age\":23}";
        //2.创建核心对象objectmapper
        ObjectMapper mapper = new ObjectMapper();
        //3.调用方法
        Person person = mapper.readValue(json, Person.class);
        System.out.println(person);//Person{name='张三', age=23, gender='男', birthday=null}
    }

}