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 blocke.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 blocke.printStackTrace();} catch (JsonMappingException e) {// TODO Auto-generated catch blocke.printStackTrace();} catch (IOException e) {// TODO Auto-generated catch blocke.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/