Jackson 对象和JSON的相互转换
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参考技术A 一、Java对象 ⇒ JSON1.1 转换方式
首先创建转换对象ObjectMappera
ObjectMapper mapper = new ObjectMapper();
该对象主要有两个转换方法
第二种方式：
mapper.writeValue(参数1，p1);
关于参数1
File：将obj对象转换为json字符串，并保存到指定的文件中
Write：将obj对象转换为json字符串，并将json填充到字符输出流中
OutputStream：将obj对象转换为json字符串，并将json填充到字节输出流中
比如：
将JSON字符串数据写入到test.txt文件中：
mapper.writeValue(new File("/Users//Desktop/test.txt"), p1);
1.2 注解使用
@JsonIgnore：排除属性
@JsonIgnore
private Date birthday;
转换最终的JSON字符串中，不会有birthday键值对。
@JsonFormat：属性值格式化
@JsonFormat(pattern = "yyyy-MM-dd HH:mm:ss")
private Date birthday;
转换结果：
“name”:“Alex”,“age”:21,“gender”:“男”,“birthday”:“2019-03-27 06:23:33”
1.3 复杂Java对象转换
List集合转换为JSON字符串：
ObjectMapper mapper = new ObjectMapper();
String json = mapper.writeValueAsString(list);
System.out.println(json);
输出结果：
[“name”:“Alex”,“age”:21,“gender”:“男”,“birthday”:“2019-03-27 06:25:23”,“name”:“Alex”,“age”:21,“gender”:“男”,“birthday”:“2019-03-27 06:25:23”,“name”:“Alex”,“age”:21,“gender”:“男”,“birthday”:“2019-03-27 06:25:23”]
Map集合转换为JSON字符串
public void test4() throws Exception
Person p1 = new Person();
p1.setName("Alex");
p1.setAge(21);
p1.setGender("男");
p1.setBirthday(new Date());
// 创建JavaBean对象
Map<String, Object> map = new HashMap<String, Object>();
// map.put("name", "Alex");
// map.put("age", "1111");
// map.put("gender", "xxx");
map.put("k1", p1);
map.put("k2", p1);
map.put("k3", p1);
// 转换
ObjectMapper mapper = new ObjectMapper();
String json = mapper.writeValueAsString(map);
System.out.println(json);
输出结果：
“k1”:“name”:“Alex”,“age”:21,“gender”:“男”,“birthday”:“2019-03-27 06:30:08”,“k2”:“name”:“Alex”,“age”:21,“gender”:“男”,“birthday”:“2019-03-27 06:30:08”,“k3”:“name”:“Alex”,“age”:21,“gender”:“男”,“birthday”:“2019-03-27 06:30:08”
二、JSON ⇒ Java对象
2.1 JSON转换为Java对象
String json = "\"name\":\"Alex\",\"age\":21,\"gender\":\"男\",\"birthday\":\"2019-03-27 06:01:54\"";
ObjectMapper mapper = new ObjectMapper();
Person person = mapper.readValue(json, Person.class);
System.out.println(person);
2.2 JSON转换为Java集合对象
String json = "[\"name\":\"Alex\",\"age\":21,\"gender\":\"男\",\"birthday\":\"2019-03-27 06:01:54\"," +
" \"name\":\"Alex\",\"age\":21,\"gender\":\"男\",\"birthday\":\"2019-03-27 06:01:54\"," +
" \"name\":\"Alex\",\"age\":21,\"gender\":\"男\",\"birthday\":\"2019-03-27 06:01:54\"]\n";
ObjectMapper mapper = new ObjectMapper();
List<Person> list = mapper.readValue(json, new TypeReference<List<Person>>() );
for (Person p : list)
System.out.println(p);
输出结果：
Personname=‘Alex’, age=21, gender=‘男’, birthday=Wed Mar 27 14:01:54 CST 2019
Personname=‘Alex’, age=21, gender=‘男’, birthday=Wed Mar 27 14:01:54 CST 2019
Personname=‘Alex’, age=21, gender=‘男’, birthday=Wed Mar 27 14:01:54 CST 2019
Jackson解析Json
JSON数据和Java对象的相互转换
* JSON解析器：
* 常见的解析器：Jsonlib，Gson，fastjson，jackson
1. JSON转为Java对象
1. 导入jackson的相关jar包
2. 创建Jackson核心对象 ObjectMapper
3. 调用ObjectMapper的相关方法进行转换
1. readValue(json字符串数据,Class)
2. Java对象转换JSON
1. 使用步骤：
1. 导入jackson的相关jar包
2. 创建Jackson核心对象 ObjectMapper
3. 调用ObjectMapper的相关方法进行转换
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
2. 注解：
1. @JsonIgnore：排除属性。
2. @JsonFormat：属性值得格式化
* @JsonFormat(pattern = "yyyy-MM-dd")
3. 复杂java对象转换
1. List：数组
2. Map：对象格式一致
测试类
import com.code_g.domain.Person;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import org.junit.Test;
import java.io.File;
import java.util.ArrayList;
import java.util.Date;
import java.util.HashMap;
public class TestJackSon {
//将java对象转换为JavaScript
@Test
public void testJack1() throws Exception {
Person person = new Person();
person.setName("code_g");
person.setAge(18);
person.setGender("male");
ObjectMapper mapper = new ObjectMapper();
// String s = mapper.writeValueAsString(person); //将对象转换为json字符串
// System.out.println(s); //{"name":"code_g","age":18,"gender":"male"}
//将对象转为json在写入文件中
mapper.writeValue(new File("E:\\\\a.txt"),person);
}
//测试注解
@Test
public void testJack2() throws Exception {
Person person = new Person();
person.setName("code_g");
person.setAge(18);
person.setGender("male");
person.setBirthday(new Date());
ObjectMapper mapper = new ObjectMapper();
String s = mapper.writeValueAsString(person);
System.out.println(s);
//{"name":"code_g","age":18,"gender":"male","birthday":1620825617349}
//加@JsonIgnore注解 {"name":"code_g","age":18,"gender":"male"}
//加@JsonFormat注解 {"name":"code_g","age":18,"gender":"male","birthday":"2021-05-12"}
}
//数组转换
@Test
public void testJack3() throws Exception {
Person person1 = new Person();
person1.setName("code_g");
person1.setAge(18);
person1.setGender("male");
person1.setBirthday(new Date());
Person person2 = new Person();
person2.setName("code_g");
person2.setAge(18);
person2.setGender("male");
person2.setBirthday(new Date());
Person person3 = new Person();
person3.setName("code_g");
person3.setAge(18);
person3.setGender("male");
person3.setBirthday(new Date());
ArrayList<Person> list = new ArrayList<>();
list.add(person1);
list.add(person2);
list.add(person3);
ObjectMapper mapper = new ObjectMapper();
String s = mapper.writeValueAsString(list);
System.out.println(s);
//[
// {"name":"code_g","age":18,"gender":"male","birthday":"2021-05-12"},
// {"name":"code_g","age":18,"gender":"male","birthday":"2021-05-12"},{
// "name":"code_g","age":18,"gender":"male","birthday":"2021-05-12"}
// ]
}
//map
@Test
public void testJack4() throws Exception {
HashMap<String, Object> map = new HashMap<>();
map.put("name","code_g");
map.put("age",18);
map.put("gender","female");
ObjectMapper mapper = new ObjectMapper();
String s = mapper.writeValueAsString(map);
System.out.println(s);
//{"gender":"female","name":"code_g","age":18}
}
//将json转换为java对象
@Test
public void testJack5() throws Exception {
String s = "{\\"gender\\":\\"female\\",\\"name\\":\\"code_g\\",\\"age\\":18}";
ObjectMapper mapper = new ObjectMapper();
Person person = mapper.readValue(s, Person.class);
System.out.println(person); //Person{name=\'code_g\', age=18, gender=\'female\', birthday=null}
}
}
Person类
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;
}
@Override
public String toString() {
return "Person{" +
"name=\'" + name + \'\\\'\' +
", age=" + age +
", gender=\'" + gender + \'\\\'\' +
", birthday=" + birthday +
\'}\';
}
public void setBirthday(Date birthday) {
this.birthday = birthday;
}
public Person(String name, int age, String gender, Date birthday) {
this.name = name;
this.age = age;
this.gender = gender;
this.birthday = birthday;
}
public Person() {
}
public Person(String name, int age, String gender) {
this.name = name;
this.age = age;
this.gender = gender;
}
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;
}
}
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