java实现System.Web.UI.ICallbackEventandler_java system.web-优快云博客

本文链接：https://blog.youkuaiyun.com/tyrone1979/article/details/1477218

本文介绍了一种使用Java和JSP实现类似ASP.NET中Callback技术的方法，通过自定义事件处理器来响应客户端请求并实时更新数据。

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早在ASP.NET 2.0 beta1时.NET就已经包含了一个异步技术叫Callback。本文将使用Java/JSP+JavaScript实现ASP.NET的Callback技术。

1．ASP.NET 2.0的Callback技术

ASP网页必须实现ICallbackEventHandler的RaiseCallbackEvent方法和GetCallbackResult方法

RaiseCallbackEvent方法负责接收Client端JavaScript所送进来的参数。GetCallbackResult负责返回结果传给Client段。

例如

Public partial class ClientCallbackSimple:System.Web.UI.page, System.Web.UI.ICallbackEventHandler

{

Public void RaiseCallbackEvent(string arg){

//do something.

}

Public sting GetCallbackResult(){

//do someting

}

ASP

<title>Callback Test</title>

function OnCallback(data)

{

Results.innerText=data;

}

</script>

</head>

<body>

<div>

</form>

</div>

</body>

</html>

其中ClientScript类负责注册Callback JavaScript函数。当按钮被点击后，程序会调用Server的RaiseCallbackEvent 方法和GetCallbackResult 方法，之后返回Client段，并调用OnCallback函数。

2．Callback的java实现

1．ICallbackEventHandler接口

接口定义为：

package org.colimas.callback;

publicinterface ICallbackEventHandler {

public Object RaiseCallbackEvent(String arg);

}

本文删掉GetCallbackResult方法，RaiseCallbackEvent方法直接返回一个结果。

2．EventHandler工厂

CallbackEventFactory类负责生成EventHandler实例。

package org.colimas.callback;

import java.util.HashMap;

publicclass CallbackEventFactory {

privatestatic HashMap handlers;

//singleton

private CallbackEventFactory(){

}

/**

*init

*@parampath

publicstaticvoid init(String path){

handlers=new HashMap();

Object value;

try {

//put all handles into handlers;

//following is a sample by only one handle.

value = Class.forName("org.colimas.handlers.ReadData").newInstance();

handlers.put("read_data", value);

} catch (InstantiationException e) {

// TODO自動生成された catch ブロック

e.printStackTrace();

} catch (IllegalAccessException e) {

// TODO自動生成された catch ブロック

e.printStackTrace();

} catch (ClassNotFoundException e) {

// TODO自動生成された catch ブロック

e.printStackTrace();

}

/**

*geteventhandlerbyhandlename

*@paramhandlerName

*@return

publicstatic ICallbackEventHandler getEventHandler(String handlerName){

return (ICallbackEventHandler)handlers.get(handlerName);

}

3．Callback Servlet

初始化CallbackEventFactory

获得Request参数，并根据参数获得EventHandler实例，调用RaiseCallbackEvent并返回结果给客户端。

package org.colimas.callback;

import java.io.IOException;

import javax.servlet.ServletException;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

/**

* Servlet implementation class for Servlet: CallbackServlet

* call event handler.

* return result.

public class CallbackServlet extends javax.servlet.http.HttpServlet implements javax.servlet.Servlet {

private static final long serialVersionUID = 1L;

/**

* init CallbackEventFactory

public void init() throws ServletException {

super.init();

CallbackEventFactory.init(this.getInitParameter("handler_path"));

}

/**

* process request

* get event handle by name

* call event handle

* return result to resposne.

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

String handlerName=(String)request.getParameter("handle");

String arg=(String)request.getParameter("arg");

if(arg==null)

arg="";

ICallbackEventHandler eventHandler=CallbackEventFactory.getEventHandler(handlerName);

String result=(String)eventHandler.RaiseCallbackEvent(arg);

response.getWriter().print(result);

}

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

doGet(request,response);

}

部署Servlet

<servlet-name>CallbackServlet</servlet-name>

<display-name>CallbackServlet</display-name>

<servlet-class>

org.colimas.callback.CallbackServlet

</servlet-class>

<init-param>

<param-name>handler_path</param-name>

<param-value>conf/handlers.properties</param-value>

</init-param>

</servlet>

<servlet-mapping>

<servlet-name>CallbackServlet</servlet-name>

<url-pattern>/callback</url-pattern>

</servlet-mapping>

4．ClientScript的实现

生成下面JavaScript代码

createXMLHttpRequest('/callback','handle=value&arg=value');

package org.colimas.callback;

/**

*registercallbackevent.

*@authortyrone

publicclass ClientScript {

publicstatic String GetCallbackEventReference(String arg,String handle){

StringBuffer js=new StringBuffer();

js.append("createXMLHttpRequest('/callback");

js.append("','handle=");

js.append(handle);

js.append("&arg='+");

js.append(arg+")");

return js.toString();

}

5．Common JSP

Common.jsp负责公用代码实现。包括，XmlHttp的实例化，发送URL请求，Server端返回后的Client端OnCallback调用。

<%@ page import="org.colimas.callback.ClientScript" %>

var xmlHttp;

function createXMLHttpRequest(url,query){

if(window.ActiveXObject){

xmlHttp=new ActiveXObject("Microsoft.XMLHTTP");

}else if(window.XMLHttpRequest){

xmlHttp=new XMLHttpRequest();

}

var path="<%=request.getContextPath()%>"+url+"?"+query;

xmlHttp.onreadystatechange=callback;

xmlHttp.open("GET",path,true);

xmlHttp.send(null);

}

function callback(){

if (xmlHttp.readyState==4){

if(xmlHttp.status==200){

var data=xmlHttp.responseText;

OnCallback(data);

}

</script>

6．测试

创建CallbackEventHandler类，自定义ICallbackEventHandler接口实现，根据Client段传送的参数，计算一个随机数。

package org.colimas.handlers;

import org.colimas.callback.ICallbackEventHandler;

import java.util.Random;

public class ReadData implements ICallbackEventHandler {

public Object RaiseCallbackEvent(String arg) {

if(arg!=null){

String data="";

Random r=new Random();

float f=r.nextFloat()* Float.valueOf(arg).floatValue();

data=new Float(f).toString();

return data;

}

return null;

}

创建JSP页面，每个1秒钟，向服务器段请求一次。：

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">

<%@ page language="java" contentType="text/html; charset=UTF-8"%>

<html>

<head>

<title>Callback Test</title>

<%@ include file="/jsp/common.jsp" %>

function DoGet()

{

//Register callbackevent

//createXMLHttpRequest('/callback','handle=read_data&arg='+form1.arg.value);

//注册CallbackEventhandle <%=ClientScript.GetCallbackEventReference("form1.arg.value","read_data")%>;

}

//OnCallback函数定义。

function OnCallback(data)

{

Results.innerText=data;

}

</script>

</head>

<div>

</form>

</div>

</body>

</html>

运行结果：

每次修改输入框内的值，下面的Text值都回动态改变。