Jackson学习一之对象与JSON互相转化

简介:

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:

 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:

 package com.jingshou.pojo;

 import java.util.List;

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

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

     }


 }

 

测试代码:

 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 stuList = new ArrayList();
         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:

 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