JSON基本用法

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JSON(JavaScriptObject Notation)是一种轻量级的数据交换格式。简单地说，JSON可以将JavaScript对象中表示的一组数据转换为字符串，然后就可以在函数之间轻松地传递这个字符串，或者在异步应用程序中将字符串从Web客户机传递给服务器端程序。这个字符串看起来有点儿古怪，但是JavaScript很容易解释它，而且JSON可以表示比"名称/值对"更复杂的结构。例如，可以表示数组和复杂的对象，而不仅仅是键和值的简单列表。

下面举几个简单的实例来介绍Json，因为JSON是javascript的原生格式，因此不需要任何特殊的API包或工具包。

实例一：

<%@ page language="java" contentType="text/html; charset=ISO-8859-1"    pageEncoding="ISO-8859-1"%><!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"><html><head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>Insert title here</title><script type="text/javascript">function testJson(){var user = {"name":"tom","age":11,"info":{"tel":"lf","cellphone":"1223"},"address":[    {"city":"lf","postcode":"111"},    {"city":"bj","postcode":"222"},]}alert(user.name);alert(user.info.cellphone);alert(user.address[1].postcode);}</script></head><body><input type="button" value="TestJson" onclick="testJson()"></body></html>

可直接运行测试。

实例二：

下面这个实例是前后台如何交互的实例，首先把环境搭起来，创建一个Maven项目json_test，具体创建过程不再赘余，pom.xml文件：

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">  <modelVersion>4.0.0</modelVersion>  <groupId>com.tgb</groupId>  <artifactId>json_test</artifactId>  <packaging>war</packaging>  <version>0.0.1-SNAPSHOT</version>  <name>json_test Maven Webapp</name>  <url>http://maven.apache.org</url>  <dependencies>    <dependency>      <groupId>junit</groupId>      <artifactId>junit</artifactId>      <version>4.0</version>      <scope>test</scope>    </dependency><dependency><groupId>commons-lang</groupId><artifactId>commons-lang</artifactId><version>2.4</version></dependency> <dependency><groupId>commons-beanutils</groupId><artifactId>commons-beanutils</artifactId><version>1.7.0</version></dependency>  <dependency><groupId>commons-collections</groupId><artifactId>commons-collections</artifactId><version>3.2</version></dependency><dependency><groupId>commons-logging</groupId><artifactId>commons-logging</artifactId><version>1.1.1</version></dependency><dependency><groupId>net.sf.ezmorph</groupId><artifactId>ezmorph</artifactId><version>1.0.6</version></dependency><dependency>        <groupId>net.sf.json-lib</groupId>        <artifactId>json-lib</artifactId>        <version>2.4</version>        <classifier>jdk15</classifier>    </dependency><dependency><groupId>org.springframework</groupId><artifactId>spring-webmvc</artifactId><version>3.0.4.RELEASE</version></dependency>                  </dependencies>  <build>    <finalName>json_test</finalName>  </build></project>

Web.xml配置如下

<?xml version="1.0" encoding="UTF-8"?><web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" id="WebApp_ID" version="2.5">  <display-name>json_test</display-name>  <welcome-file-list>    <welcome-file>index.jsp</welcome-file>  </welcome-file-list>    <servlet>  <servlet-name>springMVC</servlet-name>  <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>  <load-on-startup>1</load-on-startup>  </servlet>    <servlet-mapping>  <servlet-name>springMVC</servlet-name>  <url-pattern>/</url-pattern>  </servlet-mapping></web-app>

SpringMVC的配置文件和web.xml文件在同一个目录下，springMVC-servlet.xml：

<?xml version="1.0" encoding="UTF-8"?><beans xmlns="http://www.springframework.org/schema/beans"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xmlns:context="http://www.springframework.org/schema/context"xmlns:mvc="http://www.springframework.org/schema/mvc"xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsdhttp://www.springframework.org/schema/contexthttp://www.springframework.org/schema/context/spring-context-3.0.xsdhttp://www.springframework.org/schema/mvchttp://www.springframework.org/schema/mvc/spring-mvc-3.0.xsd"><context:component-scan base-package="com.tgb.json" /><mvc:annotation-driven /> <mvc:resources location="/js/" mapping="/js/**"/></beans>

上面关于SpringMVC的东西也不多讲，因为这不是要讲的重点。项目中还会用到Jquery，因此大家自行下载jquery包，放到webapp/js包下。

下面开始编写后台的代码，首先创建一个POJO类User：

package com.tgb.json;public class User {private String username;private int age;public String getUsername() {return username;}public void setUsername(String username) {this.username = username;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}}

然后创建TestJson类，在这个类中，我写了三个方法，是分别测试传递User对象、List集合和Map的。

package com.tgb.json;import java.io.PrintWriter;import java.util.ArrayList;import java.util.HashMap;import java.util.List;import java.util.Map;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import net.sf.json.JSONArray;import net.sf.json.JSONObject;import org.springframework.stereotype.Controller;import org.springframework.web.bind.annotation.RequestMapping;@Controllerpublic class TestJson {@RequestMapping("logon.do")public String logon(HttpServletRequest request,HttpServletResponse response){return "/test/addUser";}//返回User对象@RequestMapping("/test/json1")public void returnUser(HttpServletRequest request,HttpServletResponse response) throws Exception{response.setContentType("text/html");PrintWriter out = response.getWriter();User u1 = new User();u1.setUsername("tom1");u1.setAge(11);//Json返回实体JSONObject jsonObject = JSONObject.fromObject(u1);//返给ajax请求out.print(jsonObject);}//返回List@RequestMapping("/test/json2")public void returnList(HttpServletRequest request,HttpServletResponse response) throws Exception{response.setContentType("text/html");PrintWriter out = response.getWriter();//传递ListList<User> list = new ArrayList<User>();User u1 = new User();u1.setUsername("tom1");u1.setAge(11);User u2 = new User();u2.setUsername("jack");u2.setAge(22);list.add(u1);list.add(u2);//Json返回listJSONArray jsonArray = JSONArray.fromObject(list);//返给ajax请求out.print(jsonArray);}//返回Map@RequestMapping("/test/json3")public void returnMap(HttpServletRequest request,HttpServletResponse response) throws Exception{response.setContentType("text/html");PrintWriter out = response.getWriter();Map<String,User> map = new HashMap<String,User>();User u1 = new User();u1.setUsername("tom1");u1.setAge(11);User u2 = new User();u2.setUsername("jack");u2.setAge(22);map.put("u1", u1);map.put("u2", u2);//Json返回mapJSONObject jsonObject = JSONObject.fromObject(map);//返给ajax请求out.print(jsonObject);}}

完成了后台代码的编写，页面上就需要获取后台传过来的Json数据，并将它显示出来，创建页面testJson.jsp：

<%@ page language="java" contentType="text/html; charset=utf-8"    pageEncoding="utf-8"%><!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"><html><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8"><script type="text/javascript" src="json_test/../js/jquery-1.7.1.js"></script><title>Insert title here</title><script type="text/javascript">//获取User对象function getJsonObject(){$.ajax({type:"POST",url:"/json_test/test/json1",dataType:"json",success:function(json){alert(json.username);alert(json.age);},error:function(){alert("网络错误！");}});}//获取List对象function getJsonList(){$.ajax({type:"POST",url:"/json_test/test/json2",dataType:"json",success:function(json){alert(json[0].username);alert(json[1].age);},error:function(){alert("网络错误！");}});}//获取Map对象function getJsonMap(){$.ajax({type:"POST",url:"/json_test/test/json3",dataType:"json",success:function(json){alert(json.u1.username);alert(json.u2.age);},error:function(){alert("网络错误！");}});}</script></head><body><input type="button" value="获取User对象" onclick="getJsonObject()"><br/><input type="button" value="获取List" onclick="getJsonList()"><br/><input type="button" value="获取Map" onclick="getJsonMap()"></body></html>

通过以上这几个例子基本能说明Json的大致用途，他和XML的联系与区别，大家可自行查阅。