What is GSON and Its usage

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完整版见https://jadyer.github.io/2010/12/10/json-js/

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;@Overridepublic 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 userPeople people1 = new People();Address address1 = new Address();address1.setHomeAddress("beijing");address1.setCompanyAddress("shanghai");// 构造people1people1.setId(1);people1.setName("zhangsan");people1.setAddress(address1);// people1的朋友people11People people11 = new People();people11.setId(5);people11.setName("zhangsan's friend1");// people1的朋友people12People 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 userPeople people2 = new People();Address address2 = new Address();address2.setHomeAddress("liaoning");address2.setCompanyAddress("fujian");// 构造people2people2.setId(2);people2.setName("lisi");people2.setAddress(address2);// people1的朋友people21People people21 = new People();people21.setId(10);people21.setName("lisi's friend1");// people1的朋友people22People 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 listlist.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;}}