彗星消息发送了两次

Comet message sent twice

本文关键字：两次 消息      更新时间：2023-09-26

我想在我的项目中使用Comed，并在Tomcat7服务器上尝试了它的Jetty 8版本。它有效，但消息被发送了两次。

为了检查它是否与项目的其余部分有关，我只设置了一个具有此功能的独立项目，但我仍然收到两次消息。

我不知道为什么会这样。

项目中有5个文件：

  • pom.xml
  • web.xml
  • index.html
  • BayeuxInitializer.java
  • FormDataService.java

以下是每个文件的代码：

  • web.xml

     <?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>Sertal Vision</display-name>
    <servlet>
       <servlet-name>cometd</servlet-name>
       <servlet-class>org.cometd.server.CometdServlet</servlet-class>
       <init-param>
          <param-name>timeout</param-name>
          <param-value>60000</param-value>
       </init-param>
       <init-param>
          <param-name>logLevel</param-name>
          <param-value>3</param-value>
       </init-param>
       <load-on-startup>1</load-on-startup>
    </servlet>
    <servlet>
       <servlet-name>bayeux-init</servlet-name>
       <servlet-class>ch.sertal.server.BayeuxInitializer</servlet-class>
       <load-on-startup>2</load-on-startup>
    </servlet>
    <servlet-mapping>
       <servlet-name>cometd</servlet-name>
       <url-pattern>/cometd/*</url-pattern>
    </servlet-mapping>
    <servlet-mapping>
       <servlet-name>bayeux-init</servlet-name>
       <url-pattern>/bayeux/servlet/*</url-pattern>
    </servlet-mapping>
    <filter>
       <filter-name>continuation</filter-name>
       <filter-class>org.eclipse.jetty.continuation.ContinuationFilter</filter-class>
    </filter>
    <filter-mapping>
       <filter-name>continuation</filter-name>
       <url-pattern>/cometd/*</url-pattern>
    </filter-mapping>
    <welcome-file-list>
       <welcome-file>index.html</welcome-file>
    </welcome-file-list>
 </web-app>

  • index.html

     <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
 <html>
 <head>
    <meta http-equiv="Content-Type" content="text/html;charset=utf-8"/>
    <script type="text/javascript" src="js/dojo/dojo/dojo.js"></script>
    <script type="text/javascript">
       var subscription = undefined;
       dojo.addOnLoad( function () {
          dojo.require( "dojox.cometd" );
          dojo.require("dojox.timing");
          // Disconnect when the page unloads
          dojo.addOnUnload( function () {
             dojox.cometd.disconnect( true );
          } );
          var cometURL = "cometd";
          dojox.cometd.init( cometURL );
          var subscription = dojox.cometd.subscribe( "/sertal/formData", function ( message ) {
             dojo.create( "li", {
                innerHTML:message.data.count
             }, dojo.byId( "message-list" ) );
          } );
          i = 1;
          var t = new dojox.timing.Timer();
          t.setInterval( 1000 );
          t.onTick = function() {
             dojox.cometd.publish( '/sertal/formData', { count: i++ } );
          };
          t.start();
       } );
    </script>
 </head>
 <body>
 <div>
    <ul id="message-list"/>
 </div>
 </body>
 </html>

  • BayeuxInitializer.java

     package ch.sertal.server;
 import org.cometd.bayeux.server.BayeuxServer;
 import javax.servlet.GenericServlet;
 import javax.servlet.ServletException;
 import javax.servlet.ServletRequest;
 import javax.servlet.ServletResponse;
 import java.io.IOException;
 public class BayeuxInitializer extends GenericServlet {
    private static final long serialVersionUID = -9089442901563633963L;
    @Override
    public void init() throws ServletException {
       BayeuxServer bayeux = ( BayeuxServer ) getServletContext().getAttribute( BayeuxServer.ATTRIBUTE );
 //      new HelloService( bayeux );
       new FormDataService( bayeux, getServletContext() );
    }
    @Override
    public void service( ServletRequest servletRequest, ServletResponse servletResponse ) throws ServletException, IOException {
       throw new ServletException( "sorry :-)" );
    }
 }

  • FormDataService.java

     package ch.sertal.server;
 import org.cometd.bayeux.Message;
 import org.cometd.bayeux.server.BayeuxServer;
 import org.cometd.bayeux.server.ServerSession;
 import org.cometd.server.AbstractService;
 import javax.servlet.ServletContext;
 import java.util.Map;
 /**
  * Created by IntelliJ IDEA.
  * User: micha.roon
  * Date: 1/16/12
  * Time: 12:25 PM
  * To change this template use File | Settings | File Templates.
  */
 public class FormDataService extends AbstractService {
    private ServletContext context = null;
    public FormDataService( BayeuxServer bayeux, ServletContext context ) {
       super( bayeux, "hello" );
       this.context = context;
       addService( "/sertal/formData", "processFormData" );
       System.out.println( "New FormDataService" );
    }
    public void processFormData( final ServerSession remote, Message message ) {
       Map<String, Object> input = message.getDataAsMap();
       remote.deliver( getServerSession(), "/sertal/formData", input, null );
    }
 }

  • pom.xml

     <?xml version="1.0" encoding="UTF-8"?>
 <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/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>BayeuxTest</groupId>
    <artifactId>BayeuxTest</artifactId>
    <version>1.0</version>
    <build>
       <plugins>
          <!--compiler plugin-->
          <plugin>
             <groupId>org.apache.maven.plugins</groupId>
             <artifactId>maven-compiler-plugin</artifactId>
             <configuration>
                <source>1.6</source>
                <target>1.6</target>
             </configuration>
          </plugin>
          <plugin>
             <groupId>org.codehaus.mojo</groupId>
             <artifactId>tomcat-maven-plugin</artifactId>
             <version>1.1</version>
             <configuration>
                <username>${tomcat.username}</username>
                <password>${tomcat.password}</password>
                <url>${tomcat.manager}</url>
                <path>${tomcat.context}</path>
             </configuration>
          </plugin>
       </plugins>
    </build>
    <dependencies>
       <dependency>
          <groupId>javax.servlet</groupId>
          <artifactId>javax.servlet-api</artifactId>
          <version>3.0.1</version>
          <scope>provided</scope>
       </dependency>
       <!--for cometd support-->
       <dependency>
          <groupId>org.cometd.java</groupId>
          <artifactId>bayeux-api</artifactId>
          <version>2.3.1</version>
       </dependency>
       <dependency>
          <groupId>org.cometd.javascript</groupId>
          <artifactId>cometd-javascript-jquery</artifactId>
          <version>2.3.1</version>
          <type>war</type>
       </dependency>
       <dependency>
          <groupId>org.cometd.java</groupId>
          <artifactId>cometd-java-server</artifactId>
          <version>2.3.1</version>
       </dependency>
       <dependency>
          <groupId>org.eclipse.jetty</groupId>
          <artifactId>jetty-servlets</artifactId>
          <version>8.0.4.v20111024</version>
          <exclusions>
             <exclusion>
                <groupId>org.eclipse.jetty</groupId>
                <artifactId>jetty-client</artifactId>
             </exclusion>
          </exclusions>
       </dependency>
       <dependency>
          <groupId>javax.servlet</groupId>
          <artifactId>servlet-api</artifactId>
          <version>2.5</version>
       </dependency>
    </dependencies>
 </project>

当您使用普通频道（/sertal/formData）时，所有发布的帖子都将发送到所有订阅的客户端，在您的情况下，这是浏览器本身和Bayeux服务。因此，您将收到两个答案：一个是您发布的帖子，另一个是来自您的服务的回复。

解决方案：你不想publish你的formData，你想要它deliver ed:

      ...
      t.onTick = function() {
         dojox.cometd.deliver( '/sertal/formData', { count: i++ } );
      };
      ...

还有其他解决方案，例如使用服务信道而不是正常信道。请参阅此CometD常见问题条目以获得进一步的解释。

更新：

我保留了在我的机器上实现这一点所必需的另一个更改：dojo.require需要在addOnLoad处理程序之外调用。

     ...   
     dojo.require("dojox.cometd");
     dojo.require("dojox.timing");
     dojo.addOnLoad(function () {
         ...

我一直在使用dojo v1.7.1。

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