android:json解析的兩個工具：Gson和Jackson的使用小例子

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1.簡介

json是android與伺服器通訊過程中常用的資料格式，例如，如下是一個json格式的字串：

{"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中常用的兩個json庫為：Gson和Jackson，一下就看一下它們是如何將對象轉化為json字串，以及如何將json字串轉化為java對象。

定義Student類：

/* * $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:    [email protected] *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;}}

定義School類：

/* * $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:    [email protected] *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;}}

初始化一個School的java對象，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，進行java對象與json字串之間的相互轉換

private void testGson(){School school = initSchoolData();Gson gson = new Gson();//將對象轉化為json字串String jsonString = gson.toJson(school).toString();//列印System.out.println("GSON="+jsonString);/******分割線*****///將字串轉化為JSON對象School resultSchool = gson.fromJson(jsonString, School.class);//列印System.out.println(resultSchool.getStudents().get(0).getName());}

可見，Gson是通過toJson和fromJson兩個方法進行轉換的，使用起來十分方便。

4.使用Jackson

private void testJackson(){School school = initSchoolData();ObjectMapper objectMapper = new ObjectMapper();String jsonString = "";//將對象轉化為Json字串try {jsonString = objectMapper.writeValueAsString(school);System.out.println("Jackson="+jsonString);} catch (JsonProcessingException e) {// TODO Auto-generated catch blocke.printStackTrace();}//將json字串解析成java對象try {School resultSchool = objectMapper.readValue(jsonString, School.class);//列印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這兩個方法。此外，Jackson的writeValue和readValue有很多種參數類型，適用於多中場合。

注意：以上只是這兩個工具類的基本用法，更多瞭解，參見官方文檔。

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

Jackson：http://jackson.codehaus.org/