json与对象相互转换

package cn.itcast.test;

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

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

public class JacksonTest {

//Java对象转为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Jackson的核心对象  ObjectMapper
    ObjectMapper mapper = new ObjectMapper();
    //3.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 json = mapper.writeValueAsString(p);
    //{"name":"张三","age":23,"gender":"男"}
    //System.out.println(json);//{"name":"张三","age":23,"gender":"男"}



    //writeValue，将数据写到d://a.txt文件中
    //mapper.writeValue(new File("d://a.txt"),p);

    //writeValue.将数据关联到Writer中
    mapper.writeValue(new FileWriter("d://b.txt"),p);
}


@Test
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.转换
    ObjectMapper mapper = new ObjectMapper();
    String json = mapper.writeValueAsString(p);

    System.out.println(json);//{"name":"张三","age":23,"gender":"男","birthday":1530958029263}
                            //{"name":"张三","age":23,"gender":"男","birthday":"2018-07-07"}
}



@Test
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("张三");
    p1.setAge(23);
    p1.setGender("男");
    p1.setBirthday(new Date());

    Person p2 = new Person();
    p2.setName("张三");
    p2.setAge(23);
    p2.setGender("男");
    p2.setBirthday(new Date());


    //创建List集合
    List<Person> ps = new ArrayList<Person>();
    ps.add(p);
    ps.add(p1);
    ps.add(p2);


    //2.转换
    ObjectMapper mapper = new ObjectMapper();
    String json = mapper.writeValueAsString(ps);
    // [{},{},{}]
    //[{"name":"张三","age":23,"gender":"男","birthday":"2018-07-07"},{"name":"张三","age":23,"gender":"男","birthday":"2018-07-07"},{"name":"张三","age":23,"gender":"男","birthday":"2018-07-07"}]
    System.out.println(json);
}

@Test
public void test4() throws Exception {
    //1.创建map对象
    Map<String,Object> map = new HashMap<String,Object>();
    map.put("name","张三");
    map.put("age",23);
    map.put("gender","男");


    //2.转换
    ObjectMapper mapper = new ObjectMapper();
    String json = mapper.writeValueAsString(map);
    //{"name":"张三","age":23,"gender":"男"}
    System.out.println(json);//{"gender":"男","name":"张三","age":23}
}

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

    //2.创建ObjectMapper对象
    ObjectMapper mapper = new ObjectMapper();
    //3.转换为Java对象 Person对象
    Person person = mapper.readValue(json, Person.class);

    System.out.println(person);
}

}