JSON解析器Jackson

JSON解析器：常见的解析器：Jsonlib，Gson,fastjson,jacksonn

java对象转为JSON

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

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
• writeCalueAsString(obj):将对象转为json字符串

java代码

package com.bai.test;

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

public class JacksonTest {
    //java对象转为JSON字符串
    @Test
    public void test01() throws Exception {
        //创建person对象
        Person p = new Person();
        p.setName("张三");
        p.setAge(23);
        p.setGender("男");

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

JSON转为java对象_注解

1. @JsonIgnore:排除属性
2. @JsonFormat:属性值得格式化

 实体类

package com.bai.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 //忽略该属性
    @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 + '\'' +
                '}';
    }
}

测试类

  @Test
    public void test02() throws Exception {
        //创建person对象
        Person p = new Person();
        p.setName("张三");
        p.setAge(23);
        p.setGender("男");
        p.setBirthday(new Date());

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

        System.out.println(json);
    }

运行结果

复杂java对象转换

1.List

测试类

    @Test
    public void test03() throws Exception {
        //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
        ArrayList<Person> ps = new ArrayList<Person>();
        ps.add(p);
        ps.add(p1);
        ps.add(p2);

        //2.转换
        ObjectMapper map = new ObjectMapper();
        String json = map.writeValueAsString(ps);
        System.out.println(json);
    }

2.Map

 测试类

  @Test
    public void test04() throws Exception {
        HashMap<String, Object> map = new HashMap<String, Object>();
        map.put("name","张三");
        map.put("age",23);
        map.put("gender","男");


        ObjectMapper mapper = new ObjectMapper();
        String json = mapper.writeValueAsString(map);
        System.out.println(json);
    }
}

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)

测试类

 @Test
    public void test05() throws Exception {
        //初始值JSON字符串
        String json="{\"gender\":\"男\",\"name\":\"张三\",\"age\":23}";
        //创建ObjectMapper对象
        ObjectMapper mapper = new ObjectMapper();
        //转换为java对象 Person对象
        Person person = mapper.readValue(json, Person.class);

        System.out.println(person);
    }

运行结果