1.简单介绍

json是android与server通信过程中经常使用的数据格式，比如。例如以下是一个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中经常使用的两个json库为：Gson和Jackson，一下就看一下它们是怎样将对象转化为json字符串，以及怎样将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);
			/******切割线*****/
			//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有非常多种參数类型，适用于多中场合。

注意：以上仅仅是这两个工具类的基本使用方法，很多其它了解。參见官方文档。

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

Jackson：http://jackson.codehaus.org/