What is GSON and Its usage -

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What is GSON and Its usage

Gson的用途
在Struts2中使用JSON时，需要将序列化的属性定义在相应Action中
而我们也可以采取程序的方式，进行属性的组装，然后再生成JSON
这样的工具有很多，这里介绍一个比较强大的工具Gson
它可以直接通过Gson类的toJson()方法将Java对象转化成JSON表达式
Gson是JSON的一个Java开发包，它是由Google开发出来的
它的官方网站是http://code.google.com/p/google-gson

下面是JSON与Struts2集成的演示，其中前台页面使用了JQuery实现异步请求

首先是web.xml文件

<?xml version="1.0" encoding="UTF-8"?> <web-app version="2.5" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"> <filter> <filter-name>struts2</filter-name> <filter-class>org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter</filter-class> </filter> <filter-mapping> <filter-name>struts2</filter-name> <url-pattern>*.action</url-pattern> </filter-mapping> <welcome-file-list> <welcome-file>gsonTest.jsp</welcome-file> </welcome-file-list> </web-app>

然后是gsonTest.jsp页面

<%@ page pageEncoding="UTF-8"%> <script type="text/javascript" src="JQuery/jquery-1.4.2.js"></script> <script type="text/javascript"> function getAllInfo(){ $.post("getGson.action", {}, function(returnedData, status){ if("success" == status){ //alert(returnedData[0].address.homeAddress + "," + returnedData[0].friends[1].name); var html = "<table width='50%' border='8'><tr><th>id</th><th>name</th><th>homeAddress</th><th>companyAddress</th></tr>"; for(var i=0; i<returnedData.length; ++i){ var person = returnedData[i]; var id = person["id"]; //在JSON中这种写法也是可以的 var name = person.name; var homeAddress = person.address.homeAddress; var companyAddress = person.address.companyAddress; var tr = "<tr align='center'><td>" + id + "</td><td>" + name + "</td><td>"+ homeAddress + "</td><td>" + companyAddress + "</td></tr>"; html += tr; } html += "</table>"; $("body table:eq(0)").remove(); $("#theBody").append(html); } } ); } /**************【在JavaScript中使用JSON的第一种方式】****************************************/ //var obj = "{name: 'zhangsan'}"; //var jsonObj = eval("(" + obj + ")"); //alert(jsonObj.name); //通过JavaScript的eval()函数将字符串形式的JSON表达式转化成真正的JSON对象 //注意：eval()括号中还需要显式添加两个小括号 //补充：在http://www.json.org/js.html描述了JSON在JavaScript中的一些应用 //补充：eval()是JavaScript中很早就出现的一个函数，它的功能很强，但是容易引发一些安全问题 //补充：比如说eval()会动态的执行字符串形式的JavaScript脚本，恶意用户如果注入脚本的话就会导致页面出现危险 /**************【在JavaScript中使用JSON的第二种方式】****************************************/ //var obj2 = {name: 'lisi'}; //alert(obj2.name); //JSON实际上是JavaScript的一个子集，从JavaScript1.2开始，它里面已经包含了JSON的实现 //下面请再看一个例子 //var stu = {name:'沈浪',age:22, sex:'男',favorate:['义胆','行侠','斗智'], // say:function(){alert(this.name + "/n" + this.age + "/n" + this.favorate);}}; //alert(stu.name + " " + stu.age); //stu.say(); //调用stu中的方法 /****************************************************************************************/ </script> <body id="theBody"> <input type="button" value="Get All Info" onclick="getAllInfo()"> </body>

接着是struts.xml文件

<?xml version="1.0" encoding="UTF-8" ?> <!DOCTYPE struts PUBLIC "-//Apache Software Foundation//DTD Struts Configuration 2.1//EN" "http://struts.apache.org/dtds/struts-2.1.dtd"> <struts> <package name="struts2.1" extends="json-default"> <action name="getGson" class="com.langsin.action.GetGsonAction"/>  </package> </struts>

然后是两个POJO类

package com.langsin.bean; import java.util.List; public class People { private int id; private String name; private Address address; private List<People> friends; /*--相应变量的getter和setter略--*/ }

package com.langsin.bean; public class Address { private String homeAddress; private String companyAddress; /*--两个属性的getter和setter略--*/ }

最后是核心的GetGsonAction类

package com.langsin.action; import java.io.PrintWriter; import java.util.ArrayList; import java.util.List; import javax.servlet.http.HttpServletResponse; import org.apache.struts2.ServletActionContext; import com.google.gson.Gson; import com.langsin.bean.Address; import com.langsin.bean.People; import com.opensymphony.xwork2.ActionSupport; public class GetGsonAction extends ActionSupport { private static final long serialVersionUID = 3338016617359052243L; @Override public String execute() throws Exception { // 构造一个List对象，最终是将List转化成JSON对象 List<People> list = new ArrayList<People>(); // Info of first user People people1 = new People(); Address address1 = new Address(); address1.setHomeAddress("beijing"); address1.setCompanyAddress("shanghai"); // 构造people1 people1.setId(1); people1.setName("zhangsan"); people1.setAddress(address1); // people1的朋友people11 People people11 = new People(); people11.setId(5); people11.setName("zhangsan's friend1"); // people1的朋友people12 People people12 = new People(); people12.setId(6); people12.setName("zhangsan's friend2"); List<People> list1 = new ArrayList<People>(); list1.add(people11); list1.add(people12); people1.setFriends(list1); // Info of second user People people2 = new People(); Address address2 = new Address(); address2.setHomeAddress("liaoning"); address2.setCompanyAddress("fujian"); // 构造people2 people2.setId(2); people2.setName("lisi"); people2.setAddress(address2); // people1的朋友people21 People people21 = new People(); people21.setId(10); people21.setName("lisi's friend1"); // people1的朋友people22 People people22 = new People(); people22.setId(11); people22.setName("lisi's friend2"); // 将people21和people22添加到people2的朋友圈中 List<People> list2 = new ArrayList<People>(); list2.add(people21); list2.add(people22); people2.setFriends(list2); // put all the users into result list list.add(people1); list.add(people2); //构造好Java对象后，直接使用Gson类的toJson()方法将其转化成JSON表达式 String result = new Gson().toJson(list); //System.out.println(result); HttpServletResponse response = ServletActionContext.getResponse(); //ContentType的值不能写成【text/json】类型，否则FireBug将无法识别JSON信息 response.setContentType("application/json; charset=UTF-8"); // 取消浏览器缓存 response.setHeader("Cache-Control", "no-cache"); PrintWriter out = response.getWriter(); out.print(result); //也可以使用out.write(result) out.flush(); out.close(); return null; } }

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