DWR3 学习笔记

最新推荐文章于 2024-10-31 09:27:33 发布

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最新推荐文章于 2024-10-31 09:27:33 发布

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分类专栏： IT 文章标签： dwr spring whitespace mozilla servlet character

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本文阐述了在视频处理场景中，如何运用DWR技术进行前端发起任务、JNI录制、c++SO转换，并通过spring3监听器实现消息的实时推送。重点介绍了消息处理流程、DWR逆向推送机制及与Spring的集成方式。此外，讨论了在实施过程中遇到的异常处理、上下文获取等问题及其解决策略。

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学习需要有强大的内心作为后盾，耐着性子，一步一个脚印的向前摸索。

选择DWR的原因：

前端发起录制视频任务传送到JNI录制接口，通过c++ so进行转换，转换后调用 message handle 通知客户端。

提出问题：

转换时间不确定，转换结果不确定，不能及时反馈给客户，客户如果建立个长连接，会阻塞客户的其他业务的处理。

整体设计：

底层服务利用spring3 监听器进行so消息转换结果的监听，如果so有消息返回，则利用dwr reverse ajax 把消息推送到指定用户。

详细设计：

step1 利用spring监听器，如果so消息发布，则publish到spring容器中。

代码如下：

@Service("messageHandler" )

public class MessageHandlerImp implements IMessageHandler,

ApplicationContextAware {

final static Logger log = Logger.getLogger(MessageHandlerImp. class );

@Autowired

private IMessageService messageService ;

private final ArrayList<IMessage> messages = new ArrayList<IMessage>();

@Autowired

private MpsMessageController mpsMessageController ;

private ApplicationContext context ;

public void handler(IMessage msg) {

// mpsMessageController.convertResult();

//messageService.save(msg);

context .publishEvent( new InfoMessage(msg));

}

@Override

public void setApplicationContext(ApplicationContext context)

throws BeansException {

this . context = context;

}

step2：DWR ajax resvers是通过DWR ScripteSessionLisener进行scriptSession的创建。推送原理是，每一个用户请求会建立一个

scriptSession的数据通道，Dwr reverse 技术通过scriptsesession 发送到web端，再利用 scriptSession 与HttpSession相结合区分每一个用户的请求。

这样解决了避免多个用户都收到转换结果，从而达到，who 发起，who 接受的单点数据通信。

/**

* 扩展ScriptSessionManager.

* @author maxc

* @version 2012 - 2 - 15

public class InitScriptManager extends DefaultScriptSessionManager {

final static Logger log = Logger.getLogger(InitScriptManager. class );

public InitScriptManager() {

addScriptSessionListener( new ScriptSessionListener() {

public void sessionCreated(ScriptSessionEvent event) {

ScriptSession scriptSession = event.getSession(); // 获取新创建的SS

HttpSession httpSession = WebContextFactory.get().getSession(); // 获取构造SS的用户的HttpSession

String userId = (String) httpSession.getAttribute( "userId" );

if (userId == null ) {

scriptSession.invalidate();

httpSession.invalidate();

return ;

}

log .info( "创建 ===============" + scriptSession.getId());

scriptSession.setAttribute( "userId" , userId); // 此处将userId和scriptSession绑定

}

public void sessionDestroyed(ScriptSessionEvent event) {

log .info( "销毁 ===============" + event.getSession().getId());

}

});

/**

* @author xiaochao.ma

* <p> 不用spring3注入是因为一旦交给spring3容器处理，就会重新生成一个 mannager，反转业务就不能使用唯一的监听器监听scriptSession的创建 <p>

* 注入DWRReservers 使得反转业务可以应用scriptManager 这样就可以获得当前应用的scriptSession

DWRReservers. manager = this ;

}

step3：配置dwr

<?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" >

< listener >

< listener-class > org.springframework.web.context.ContextLoaderListener </ listener-class >

</ listener >

< context-param >

< param-name > springconfig </ param-name >

< param-value > /WEB-INF/applicationContext.xml,/WEB-INF/spring3-servlet.xml </ param-value >

</ context-param >

< filter >

< filter-name > Set Character Encoding </ filter-name >

< filter-class > org.springframework.web.filter.CharacterEncodingFilter </ filter-class >

< init-param >

< param-name > encoding </ param-name >

< param-value > UTF-8 </ param-value >

</ init-param >

< init-param >

< param-name > forceEncoding </ param-name >

< param-value > true </ param-value >

</ init-param >

</ filter >

< filter-mapping >

< filter-name > Set Character Encoding </ filter-name >

< url-pattern > /* </ url-pattern >

</ filter-mapping >

< servlet >

< servlet-name > spring3 </ servlet-name >

< servlet-class > org.springframework.web.servlet.DispatcherServlet </ servlet-class >

< init-param >

< param-name > contextConfigLocation </ param-name >

< param-value >

/WEB-INF/applicationContext.xml,/WEB-INF/spring3-servlet.xml

</ param-value >

</ init-param >

< load-on-startup > 1 </ load-on-startup >

</ servlet >

< servlet-mapping >

< servlet-name > spring3 </ servlet-name >

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

</ servlet-mapping >

<!-- <servlet>

<servlet-name>initScript</servlet-name>

<servlet-class>com.gnetis.mpagent.controller.InitScriptSession</servlet-class>

<load-on-startup>2</load-on-startup>

</servlet> -->

< servlet >

< servlet-name > dwr-invoker </ servlet-name >

< servlet-class > org.directwebremoting.servlet.DwrServlet </ servlet-class >

< init-param >

< param-name > debug </ param-name >

< param-value > false </ param-value >

</ init-param >

< init-param >

< param-name > crossDomainSessionSecurity </ param-name >

< param-value > false </ param-value >

</ init-param >

< init-param >

< param-name > pollAndCometEnabled </ param-name >

< param-value > true </ param-value >

</ init-param >

< init-param >

< param-name > allowScriptTagRemoting </ param-name >

< param-value > true </ param-value >

</ init-param >

< init-param >

< param-name > org.directwebremoting.extend.ScriptSessionManager </ param-name >

< param-value > com.gnetis.mpagent.controller.InitScriptManager </ param-value >

</ init-param >

< load-on-startup > 1 </ load-on-startup >

</ servlet >

< servlet-mapping >

< servlet-name > dwr-invoker </ servlet-name >

< url-pattern > /dwr/* </ url-pattern >

</ servlet-mapping >

< welcome-file-list >

< welcome-file > index.jsp </ welcome-file >

</ welcome-file-list >

</ web-app >

step3：Spring3监听到消息后，交由DWR ajax reverse技术进行推送。

代码如下：

package com.gnetis.mpagent.service.imp;

import java.util.Collection;

import java.util.concurrent.ScheduledThreadPoolExecutor;

import javax.servlet.ServletContext;

import org.apache.log4j.Logger;

import org.directwebremoting.ScriptBuffer;

import org.directwebremoting.ScriptSession;

import org.directwebremoting.annotations.RemoteMethod;

import org.directwebremoting.guice.ScriptSessionScoped;

import org.springframework.beans.factory.annotation.Autowired;

import org.springframework.context.ApplicationEvent;

import org.springframework.context.ApplicationListener;

import org.springframework.web.context.ServletContextAware;

import com.gnetis.mpagent.controller.InitScriptManager;

import com.gnetis.mpagent.service.MpsConvertTaskResultService;

import com.gnetis.tang.agent.message.IMessage;

import com.gnetis.tang.agent.message.InfoMessage;

public class DWRReservers implements ApplicationListener, ServletContextAware {

@Autowired

private MpsConvertTaskResultService mpsConvertTaskResultService ;

final static Logger log = org.apache.log4j.Logger

. getLogger(DWRReservers.class);

static ScheduledThreadPoolExecutor executor = new ScheduledThreadPoolExecutor(

1);

public static InitScriptManager manager;

private ServletContext servletContext;

@RemoteMethod

@ScriptSessionScoped

public void reverseMessage(final IMessage message) {

log.info("DWRReservers reverseMessage :: active[" + active

+ "] message[" + message + "]" );

if (message == null) {

active = true ;

} else {

log.info(" reverseMessage :: message====>" + message);

Collection<ScriptSession> ss = manager.getAllScriptSessions();

for (ScriptSession scriptsession : ss) {

Object userId = scriptsession.getAttribute("userId" );

log.info("ScriptSessionId [" + scriptsession.getId()

+ "]userId[" + scriptsession.getAttribute("userId" )

+ "]");

if (userId != null

&& (userId.toString()).equals(message.getSessionId())) {

scriptsession.addScript( new ScriptBuffer()

.appendScript( "receiveMessages").appendScript("(" )

.appendData(message).appendScript( ");"));// 找到符合要求的，推送事件

}

active = false ;

}

public DWRReservers() {

}

public synchronized void isReceive(final int confId, final String sessionId) {

log.info(" isRecive :: jsp invork function paremeter are [" + confId

+ "]");

mpsConvertTaskResultService.convert(confId, sessionId);

}

/**

* is receive

protected transient boolean active = true;

@Override

public void setServletContext(ServletContext servletContext) {

this.servletContext = servletContext;

}

@Override

public void onApplicationEvent(ApplicationEvent event) {

// TODO Auto-generated method stub

if (event instanceof InfoMessage) {

IMessage message = (IMessage) event.getSource();

log.info("onApplicationEvent :: message [" + message.getMsgID()

+ " " + message.getSessionId() + " ]" );

reverseMessage(message);

}

step4：jsp发起的请求通道。

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

pageEncoding="utf-8" %>

<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>

<%@ taglib prefix="fmt" uri="http://java.sun.com/jsp/jstl/fmt" %>

<%@ taglib prefix="fn" uri="http://java.sun.com/jsp/jstl/functions" %>

<%@page import="org.directwebremoting.ScriptSession" %>

<%@page import="org.directwebremoting.Container" %>

<%@page import="org.directwebremoting.ServerContextFactory" %>

<%@page import="org.directwebremoting.extend.ScriptSessionManager" %>

<%@page import="org.directwebremoting.event.ScriptSessionListener" %>

String path = request.getContextPath();

String basePath = request.getScheme() + "://"

+ request.getServerName() + ":" + request.getServerPort()

+ path + "/";

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd" >

<head>

<title> Insert title here</title >

table {

width: 600px ;

margin: 0px auto ;

font: Georgia 11px ;

color: #333333 ;

text-align: center ;

border-collapse: collapse ;

}

tr {

border: 1px solid black ;

margin: 0px ;

cellspacing: "1" cellpadding :"0"

}

td {

border: 1px solid blue ;

margin: 0px ;

cellspacing: "1" cellpadding :"0"

}

</style>

dwr.engine._errorHandler=function(message ,ex){

dwr.engine._debug( "Error: " + ex.name + ", " + ex.message, true);

if (message == null || message == "") alert( "A server error has occurred.");

// Ignore NS_ERROR_NOT_AVAILABLE if Mozilla is being narky

else if (message.indexOf("0x80040111") != -1) dwr.engine._debug(message);

else ;//alert(message);

}

function dwrconvert(confId) {

//alert(confId);

dwrService.isReceive(confId, '<%=session.getAttribute("userId" ).toString()%>');

}

function objectEval(text) {

// eval() breaks when we use it to get an object using the { a:42, b:'x' }

// syntax because it thinks that { and } surround a block and not an object

// So we wrap it in an array and extract the first element to get around

// this.

// This code is only needed for interpreting the parameter input fields,

// so you can ignore this for normal use.

// The regex = [start of line][whitespace]{[stuff]}[whitespace][end of line]

text = text.replace(/\n/g, ' ');

text = text.replace(/\r/g, ' ');

if (text.match(/^\s*\{.*\}\s*$/)) {

text = '[' + text + '][0]' ;

}

return eval(text);

}

function receiveMessages(data) {

if (data != null && typeof data == 'object') {

var jsMessage = objectEval(dwr.util.toDescriptiveString(data, 2));

var message = "" ;

var confId = jsMessage["confId" ];

var msgID = jsMessage["msgID" ];

message = "confId : [" + confId + "] , msgID : [" + msgID + "]";

var errorId = jsMessage["errorId" ];

var progressValue = jsMessage["progressValue" ];

var url = jsMessage["url" ];

if (errorId) {

message += ",errorId : [" + errorId + "]" ;

}

if (progressValue) {

message += ",progressValue : [" + progressValue + "]";

}

if (url) {

/* var href=document.createElement("a");

href.attributes("href",url); */

message += ",url : <a href='"+url+"'> " + url + "</a>";

}

document.getElementById( "d0").innerHTML = message;

//dwr.util.setValue('d0', message);

} else {

dwr.util.setValue( 'd0', dwr.util.toDescriptiveString(data, 1));

}

</script>

</head>

<body

onload="dwr.engine.setActiveReverseAjax(true);dwr.engine.setNotifyServerOnPageUnload(true);" >

<div>

<table>

<tr>

<td> modelId</td >

<td> convert</td >

</tr>

<c:forEach var="maps" items="${tasks } " >

<c:forEach var="o" items=" ${maps.mpsConvertTasks}" varStatus="sta" >

<tr>

<td> ${ o.confId}</td >

<td> ${ o.groupID}</td >

<td> ${ o.serviceType}</td >

<td> ${ o.startTime}</td >

<td> ${ o.endTime}</td >

<td> ${ o.addTime}</td >

<td> ${ o.modelId}</td >

<c:if test=" ${sta.count==1 }">

<a href="#" onclick="dwrconvert('${ o.id}')">converr </a>

</td>

</c:if>

</tr>

</c:forEach>

</table>

</div>

</body>

</html>

总结：如果用spring3的 DwrServelt配置反转mananger 报：

No bean named '__dwrConfiguration' is defined

原因不明，猜测是由于dwr版本问题造成的。DWR反转与spring3相结合的comet方式没有很好得解决方案，dwr在spring容器下不能获得context，本项目采用分离处理。不用 spring实现的dwrservlet。详细见web.xml配置。

DWR.xml 代码：

<?xml version="1.0" encoding= "UTF-8"?>

<!DOCTYPE dwr PUBLIC

"-//GetAhead Limited//DTD Direct Web Remoting 1.0//EN"

"http://www.getahead.ltd.uk/dwr/dwr10.dtd" >

<dwr>

<allow>

</create>

<convert converter="bean"

match="com.gnetis.tang.agent.message.MessageProgress" />

<convert converter="bean"

match="com.gnetis.tang.agent.message.MessageSuccess" />

<convert converter="bean"

match="com.gnetis.tang.agent.message.MessageFailure" />

</allow>

</dwr>

异常2：自己写servlet监听scriptSession的创建汇报 WebContextFactory. get()为NULL 异常，DWR context 必须在servlet容器中，自己写的servlet 没有发起请求时候，init是不能够获取到httpSession的。解决方案就是在DWR 自己的context中配置参数，实现defaultScriptSessionManager。详细见 web.xml。

异常3：dwr消息错误监听，当没有sessionScript建立时候，后台调用invalidSession方法会被dwr._debug接受并错误的弹出alert.

解决方案，重写dwr处理消息的机制，此项目中忽略了错误消息，若有需要可以写到后台日志中。

代码：

dwr.engine._errorHandler= function(message ,ex){

dwr.engine._debug( "Error: " + ex.name + ", " + ex.message, true );