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: -5-12 $
* Copyright (C) ZhengHaibo, Inc. All rights reserved.
* This software is Made by Zhenghaibo.
*/
package com.example.testjson;
/*
*@author: ZhengHaibo
*web: /nuptboyzhb
*mail: [emailprotected]
*-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: -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: /nuptboyzhb
*mail: [emailprotected]
*-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;
}
}
初始化一个School的java对象,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。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。