Question

我有一个使用CometProcessor接口的简单servlet。

package cc.co.sqeezer;

import java.io.IOException;

public class TestServlet extends HttpServlet implements CometProcessor {
 private static final long serialVersionUID = 1L;

    public TestServlet() {
        super();
    }

    public void event(CometEvent event) {
     if (event.getEventType() == CometEvent.EventType.BEGIN)
     {
      System.out.println("Begin");
      event.getHttpServletRequest().setAttribute("org.apache.tomcat.comet.timeout", new Integer(0xFFFFFFFF));
      send(event);
     }
     else if (event.getEventType() == CometEvent.EventType.READ)
     {
      System.out.println("Read");
      send(event);
     }
     else if (event.getEventType() == CometEvent.EventType.END)
     {
      System.out.println("End: " + event.getEventSubType());
      send(event);
     }
     else if (event.getEventType() == CometEvent.EventType.ERROR)
     {
      System.out.println("Error: " + event.getEventSubType());
      send(event);
     }

    }

 private void send(CometEvent event) {
  HttpServletResponse response = event.getHttpServletResponse();
  response.setHeader("Pragma", "no-cache");
  response.setHeader("Cache-Control", "must-revalidate");
  response.setHeader("Cache-Control", "no-cache");
  response.setHeader("Cache-Control", "no-store");
  response.setDateHeader("Expires", 0);

  String eventType = event.getEventType().toString();
  String receivedText = (String) event.getHttpServletRequest().getParameter("mytext");
  try {
   response.getWriter().write(eventType + " " + receivedText);
   response.getWriter().flush();
  } catch (IOException e) {
   e.printStackTrace();
  }
 }

 public void init(ServletConfig config) throws ServletException {
 }

}

连接器

    <Connector port="8080" protocol="org.apache.coyote.http11.Http11NioProtocol" 
           connectionTimeout="20000" 
           URIEncoding="UTF-8"
           redirectPort="8443" />

Jsp页面是

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Test</title>
</head>
<body>
<script type="text/javascript"><!--

 function createRequestObject() {
   if (typeof XMLHttpRequest === 'undefined') {
     XMLHttpRequest = function() {
       try { return new ActiveXObject("Msxml2.XMLHTTP.6.0"); }
         catch(e) {}
       try { return new ActiveXObject("Msxml2.XMLHTTP.3.0"); }
         catch(e) {}
       try { return new ActiveXObject("Msxml2.XMLHTTP"); }
         catch(e) {}
       try { return new ActiveXObject("Microsoft.XMLHTTP"); }
         catch(e) {}
       throw new Error("This browser does not support XMLHttpRequest.");
     };
   }
   return new XMLHttpRequest();
 }

 var req = createRequestObject();


 function sendData()
 {


  if (req) {       
         req.open("POST", "TestServlet", true);
         req.setRequestHeader("If-Modified-Since", "Sat, 1 Jan 2000 00:00:00 GMT");
         req.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
         var params = "mytext=" + document.getElementById("mytext").value;
         //req.setRequestHeader("Content-length", params.length);

         req.onreadystatechange = processReqChange;
         req.send(params);
     }
 }

 function processReqChange()
 {
  try 
  {
      if (req.readyState == 4) {
          alert(req.status + " ReadyState=4 " + req.responseText);
      }
      if (req.readyState == 3) {
       alert(req.status + " ReadyState=3 " + req.responseText);
      }
      if (req.readyState == 2) {
          alert(req.status + " ReadyState=2 " + req.responseText);
      }
      if (req.readyState == 1) {
       alert(req.status + " ReadyState=1 " + req.responseText);
      }
  }
  catch( e ) {
        //alert("Error: " + e.description);
  }

 }

--></script>
<input id="mytext" type="text"></input>
<input type="button" value="send" onclick="sendData()"></input>
</body>
</html>

我正在使用Eclipse来启动servlet 我期望的是将“文本”发送到服务器并使用相同的文本和CometEvent名称返回echo。当我将数据发送到服务器时，我首先得到“200 ReadyState = 3 BEGIN text”。这是预期的情况。如果我等待大约25秒，我将在控制台输出中得到“错误：超时”。并且错误事件将每25秒触发一次，因此在浏览器中我看到类似“200 ReadyState = 3 BEGIN textERROR textERROR textERROR textERROR textERROR text”，其中“text”是输入中的文本。 5 textERROR表示发生了5个错误事件。我不知道为什么这些textERROR出现了。主要问题是为什么错误事件（超时）每25秒触发一次？如果我在浏览器中关闭客户端，我将获得无限循环的结束事件。为什么会发生这种情况我也不知道？如何防止这种循环？
Tomcat版本是Ubuntu 10.10上的Apache Tomcat / 6.0.28 提前谢谢你。

Answer 1

首先，您可以像这样设置请求的超时，

if (event.getEventType() == CometEvent.EventType.BEGIN) {
    event.setTimeout(60 * 1000);
    ...
}
...

25秒可能是默认值。

发生超时时发送错误，因此每25秒

response.getWriter().write(eventType + " " + receivedText);

在你的代码中发送“错误文本”，而不是textERROR，在你的响应结尾添加一个新行来验证这一点。

无限循环的原因是你没有关闭事件。调用CometEvent ERROR或END时，必须调用event.close（），

else if (event.getEventType() == CometEvent.EventType.END){
    event.close();
....

这很可能是你无限循环的原因。

请阅读documentation，它解释了您遇到的大多数问题。

CometProcessor结束事件循环

1 个答案: