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导入jackson的相关jar包
创建Jackson核心对象 ObjectMapper
调用ObjectMapper的相关方法进行转换
1. readValue(json字符串数据,Class)
map对象写法
Map<String,Object> map = new HashMap<String,Object>();
map.put(“name”,“张三”);
list集合写法
//创建List集合
List ps = new ArrayList();
ps.add§;
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):
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);
