android:json解析的两个工具：Gson和Jackson的使用小例子

1.简介

json是android与服务器通信过程中常用的数据格式，例如，如下是一个json格式的字符串：

{"address":"Nanjing","name":"NUPT","students":[{"name":"stu1","id":"10000","age":20},{"name":"stu1","id":"10001","age":21},{"name":"stu1","id":"10002","age":22}]}

2.android中常用的两个json库为：Gson和Jackson，一下就看一下它们是如何将对象转化为json字符串，以及如何将json字符串转化为java对象。

定义Student类：

/*
* $filename: Student.java,v $
* $Date: 2014-5-12  $
* Copyright (C) ZhengHaibo, Inc. All rights reserved.
* This software is Made by Zhenghaibo.
*/
package com.example.testjson;
/*
*@author: ZhengHaibo
*web:     http://blog.csdn.net/nuptboyzhb *mail:    zhb931706659@126.com
*2014-5-12  Nanjing,njupt,China
*/
public class Student {
private String name;
private String id;
private int age;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
}

定义School类：

/*
* $filename: School.java,v $
* $Date: 2014-5-12  $
* Copyright (C) ZhengHaibo, Inc. All rights reserved.
* This software is Made by Zhenghaibo.
*/
package com.example.testjson;

import java.util.List;
/*
*@author: ZhengHaibo
*web:     http://blog.csdn.net/nuptboyzhb *mail:    zhb931706659@126.com
*2014-5-12  Nanjing,njupt,China
*/
public class School {
private String name;
private String address;
List<Student> students;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getAddress() {
return address;
}
public void setAddress(String address) {
this.address = address;
}
public List<Student> getStudents() {
return students;
}
public void setStudents(List<Student> students) {
this.students = students;
}
}

初始化一个School的java对象，待使用：

private School initSchoolData(){
School school = new School();
school.setAddress("Nanjing");
school.setName("NUPT");
List<Student> list = new ArrayList<Student>();
for(int i= 0;i<3;i++){
Student student = new Student();
student.setAge(20+i);
student.setId("1000"+i);
student.setName("stu"+1);
list.add(student);
}
school.setStudents(list);
return school;
}

3.使用Gson，进行java对象与json字符串之间的相互转换

private void testGson(){
School school = initSchoolData();
Gson gson = new Gson();
//将对象转化为json字符串
String jsonString = gson.toJson(school).toString();
//打印
System.out.println("GSON="+jsonString);
/******分割线*****/
//将字符串转化为JSON对象
School resultSchool = gson.fromJson(jsonString, School.class);
//打印
System.out.println(resultSchool.getStudents().get(0).getName());
}

可见，Gson是通过toJson和fromJson两个方法进行转换的，使用起来十分方便。

4.使用Jackson

private void testJackson(){
School school = initSchoolData();
ObjectMapper objectMapper = new ObjectMapper();
String jsonString = "";
//将对象转化为Json字符串
try {
jsonString = objectMapper.writeValueAsString(school);
System.out.println("Jackson="+jsonString);
} catch (JsonProcessingException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
//将json字符串解析成java对象
try {
School resultSchool = objectMapper.readValue(jsonString, School.class);
//打印
System.out.println(resultSchool.getStudents().get(0).getName());
} catch (JsonParseException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (JsonMappingException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}

使用Jackson，主要是使用writeValueAsString和readValue这两个方法。此外，Jackson的writeValue和readValue有很多种参数类型，适用于多中场合。

注意：以上只是这两个工具类的基本用法，更多了解，参见官方文档。

Gson文档： http://code.google.com/p/google-gson/

Jackson： http://jackson.codehaus.org/