Jackson學習一之對象與JSON互相轉化

簡介:

Jackson是一個流行的基於Java的JSON處理框架

官方wiki:http://wiki.fasterxml.com/JacksonInFiveMinutes

官方文檔:http://wiki.fasterxml.com/JacksonDocumentation

學習參考: Json轉換利器Gson之實例 系列,順便也學習一下GSON

 

本篇簡介如何使用Jackson進行Java對象與JSON的互相轉換

新建基本Student類:

package com.jingshou.pojo;

import java.util.Date;

public class Student {
    private int id;
    private String name;
    private Date birthDay;

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Date getBirthDay() {
        return birthDay;
    }

    public void setBirthDay(Date birthDay) {
        this.birthDay = birthDay;
    }

    @Override
    public String toString() {
        return "Student [birthDay=" + birthDay + ", id=" + id + ", name="
                + name + "]";
    }

}

 班級類:

package com.jingshou.pojo;

import java.util.List;

public class Class {
    private String cname;
    private List<Student> members;
    public String getCname() {
        return cname;
    }
    public void setCname(String cname) {
        this.cname = cname;
    }
    public List<Student> getMembers() {
        return members;
    }
    public void setMembers(List<Student> members) {
        this.members = members;
    }

    public String toString(){
        return "The Class Name is: " + cname + " " + "The members are: " + members;

    }


}

 

測試代碼:

package com.jingshou.jackson;

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

import com.fasterxml.jackson.databind.ObjectMapper;
import com.jingshou.pojo.Class;
import com.jingshou.pojo.Student;

public class JacksonTest1 {

    public static void main(String[] args) throws IOException {
        Student student1 = new Student();
        student1.setId(5237);
        student1.setName("jingshou");
        student1.setBirthDay(new Date());

        ObjectMapper mapper = new ObjectMapper();

        // Convert object to JSON string
        String Json =  mapper.writeValueAsString(student1);
        System.out.println("Change Object to JSON String: " + Json);

        // Convert Json string to Object
        Student student2 = mapper.readValue(Json, Student.class);
        System.out.println(student2);

        // Create a student list add it to Bj
        Student student3 = new Student();
        student3.setId(5117);
        student3.setName("saiya");
        student3.setBirthDay(new Date());

        List<Student> stuList = new ArrayList<Student>();
        stuList.add(student1);
        stuList.add(student3);

        Class bj = new Class();
        bj.setCname("五年二班");
        bj.setMembers(stuList);

        String json2 = mapper.writeValueAsString(bj);
        System.out.println("The JSON from Class is: " + json2);

        Class bj2 = mapper.readValue(json2, Class.class);
        System.out.println(bj2);


    }

}

 運行結果:

Change Object to JSON String: {"id":5237,"name":"jingshou","birthDay":1389513906622}
Student [birthDay=Sun Jan 12 16:05:06 CST 2014, id=5237, name=jingshou]
The JSON from Class is: {"cname":"五年二班","members":[{"id":5237,"name":"jingshou","birthDay":1389513906622},{"id":5117,"name":"saiya","birthDay":1389513906859}]}
The Class Name is: 五年二班 The members are: [Student [birthDay=Sun Jan 12 16:05:06 CST 2014, id=5237, name=jingshou], Student [birthDay=Sun Jan 12 16:05:06 CST 2014, id=5117, name=saiya]]

 

小結:

• 轉換的關鍵就是ObjectMapper 
• 在使用ObjectMapper對象readValue或者writeValue的時候,JSON可以以字符串的形式傳入,也可以以文件的形式傳入,官方的例子是讓將JSON保存在文件中
• 明顯JSON字串中的key與Java類中的field名字應該要相同
• Student類如果有自定義構造函數的時候,進行JSON->對象轉換會出錯,接下去再研究這個問題..
• Date域是以long類型輸出的,有必要的話,需要進行格式轉換
• 
  
• 轉自：http://lijingshou.iteye.com/blog/2003020