Java对象与JSON字符串互相转换

package com.json.pojo;

import java.util.Date;

import com.fasterxml.jackson.annotation.JsonFormat;

/**
 * 一个人的对象类
 * @author xuexue
 *
 */
public class Person {
	//姓名
	private String name;
	
	//年龄
	private int age;
	
	//地址
	private String address;
	
	//日期
	@JsonFormat(pattern = "yyyy/MM/dd hh:mm:ss")
	private Date date;

	public Date getDate() {
		return date;
	}

	public void setDate(Date date) {
		this.date = date;
	}

	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 getAddress() {
		return address;
	}

	public void setAddress(String address) {
		this.address = address;
	}

	@Override
	public String toString() {
		return "Person [name=" + name + ", age=" + age + ", address=" + address + ", date=" + date + "]";
	}

	
}

package com.json.test;


import java.io.IOException;
import java.util.ArrayList;
import java.util.Date;
import java.util.HashMap;
import java.util.List;

import org.junit.jupiter.api.Test;

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.json.pojo.Person;

/**
 * Person对象转为JSON字符串
 * @author xuexue
 *
 */
public class Testt {
	
	@Test
	public void test() throws JsonProcessingException {
		//1、创建Person对象
		Person person = new Person();
		person.setName("张三");
		person.setAge(20);
		person.setAddress("河源市");
		person.setDate(new Date());
		
		//2、创建Jackson核心对象，ObjectMapper
		ObjectMapper mapper = new ObjectMapper();

		//3、person对象转为JSON字符串
		String valueAsString = mapper.writeValueAsString(person);
		System.out.println(valueAsString);//{"name":"张三","age":20,"address":"河源市","date":"2019/09/05 10:36:27"}
	}
	
	@Test
	public void test2() throws JsonProcessingException {
		//1、创建Map集合
		HashMap<String, Object> map = new HashMap<>();
		map.put("name", "lisi");
		map.put("age", 33);
		map.put("address", "河源");
		
		
		//2、创建Jackson核心对象，ObjectMapper
		ObjectMapper mapper = new ObjectMapper();

		//3、person对象转为JSON字符串
		String valueAsString = mapper.writeValueAsString(map);
		System.out.println(valueAsString);//{"address":"河源","name":"lisi","age":33}
	}
	
	@Test
	public void test3() throws JsonProcessingException {
		//1、创建Map集合
		List<Person> list = new ArrayList<Person>();
		list.add(new Person());
		list.add(new Person());
		list.add(new Person());
		
		
		//2、创建Jackson核心对象，ObjectMapper
		ObjectMapper mapper = new ObjectMapper();

		//3、person对象转为JSON字符串
		String valueAsString = mapper.writeValueAsString(list);
		System.out.println(valueAsString);//[{"name":null,"age":0,"address":null,"date":null},{"name":null,"age":0,"address":null,"date":null},{"name":null,"age":0,"address":null,"date":null}]
	}
}

	@Test
	public void test4() throws IOException {
		//1、创建JSON串
		String json = "{\"address\":\"河源\",\"name\":\"lisi\",\"age\":33}";
		//2、创建Jackson核心对象，ObjectMapper
		ObjectMapper mapper = new ObjectMapper();

		//3、JSON字符串转为Person对象
		Person person = mapper.readValue(json, Person.class);
		System.out.println(person);//[{"name":null,"age":0,"address":null,"date":null},{"name":null,"age":0,"address":null,"date":null},{"name":null,"age":0,"address":null,"date":null}]
	}