1.簡單介紹

json是android與server通信過程中經常使用的數據格式，比如。例如以下是一個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中經常使用的兩個json庫為：Gson和Jackson，一下就看一下它們是怎樣將對象轉化為json字符串，以及怎樣將json字符串轉化為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 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 getStudents() {

return students;

}

public void setStudents(List 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 list = new ArrayList();

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字符串之間的相互轉換

private void testGson(){

School school = initSchoolData();

Gson gson = new Gson();

//將對象轉化為json字符串

String jsonString = gson.toJson(school).toString();

//打印

System.out.println("GSON="+jsonString);

/******切割線*****/

//將字符串轉化為JSON對象

School resultSchool = gson.fromJson(jsonString, School.class);

//打印

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字符串

try {

jsonString = objectMapper.writeValueAsString(school);

System.out.println("Jackson="+jsonString);

} catch (JsonProcessingException e) {

// TODO Auto-generated catch block

e.printStackTrace();

}

//將json字符串解析成java對象

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這兩個方法。此外。Jackson的writeValue和readValue有非常多種參數類型，適用于多中場合。

注意：以上僅僅是這兩個工具類的基本使用方法，很多其它了解。參見官方文檔。

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