Jackson学习一之对象与JSON互相转化

原文地址：http://lijingshou.iteye.com/blog/2003020



Jackson是一个流行的基于Java的JSON处理框架
官方wiki:http://wiki.fasterxml.com/JacksonInFiveMinutes
官方文档:http://wiki.fasterxml.com/JacksonDocumentation
学习参考: Json转换利器Gson之实例 系列,顺便也学习一下GSON

本篇简介如何使用Jackson进行Java对象与JSON的互相转换
新建基本Student类:
Java代码  收藏代码
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 + "]"; 
    } 
 
} 
班级类:
Java代码  收藏代码
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; 
         
    } 
     
 
} 

测试代码:
Java代码  收藏代码
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); 
         
 
    } 
 
} 
运行结果:
Text代码  收藏代码
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]] 

小结:
转换的关键就是ObjectMapper
在使用ObjectMapper对象readValue或者writeValue的时候,JSON可以以字符串的形式传入,也可以以文件的形式传入,官方的例子是让将JSON保存在文件中
明显JSON字串中的key与Java类中的field名字应该要相同
Student类如果有自定义构造函数的时候,进行JSON->对象转换会出错,接下去再研究这个问题..
Date域是以long类型输出的,有必要的话,需要进行格式转换
本文出自"lijingshou"博客，请务必保留此出处http://lijingshou.iteye.com/blog/2003020