Tomcat6 comet, IE浏览器不支持Streaming ajax的解决方法小记

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Comet

Comet 浏览器 IE Ajax PHP

IE只不支持Streaming的。所以不能通过以下的代码来拿到comet的数据。

     if (request.readyState == 3) {
       if (request.status == 200) {
         var increaseText = request.responseText.substring(index);
           document.getElementById("cmessage").innerHTML =  increaseText;
           document.getElementById("message").innerHTML =  document.getElementById("message").innerHTML + increaseText;
           index = request.responseText.length;
           document.getElementById("status").innerHTML = document.getElementById("status").innerHTML + "connected....<br>";
       } else{
         alert("status is " + request.status);
       }
     }else if (request.readyState==4 && request.status == 200){
         document.getElementById("status").innerHTML = document.getElementById("status").innerHTML +  "connection rest, try to re-connect.<br>";
         connectComet();
         index=0;
     }

但是我们可以通过iframe的方法，但是用iframe的话浏览器会显示烦人的进度条。我们可以通过以下的代码来避免。

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
  <head>
    <title>Comet demo</title>
    <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
    <script type="text/javascript" src="prototype.js"></script>
  </head>
  <body>
    <div id="content">The server time will be shown here</div>

<script type="text/javascript">
var comet = {
  connection   : false,
  iframediv    : false,

  initialize: function() {
    if (navigator.appVersion.indexOf("MSIE") != -1) {

      // For IE browsers
      comet.connection = new ActiveXObject("htmlfile");
      comet.connection.open();
      comet.connection.write("<html>");
      comet.connection.write("<script>document.domain = '"+document.domain+"'");
      comet.connection.write("</html>");
      comet.connection.close();
      comet.iframediv = comet.connection.createElement("div");
      comet.connection.appendChild(comet.iframediv);
      comet.connection.parentWindow.comet = comet;
      comet.iframediv.innerHTML = "<iframe id='comet_iframe' src='./backend.php'></iframe>";

    } else if (navigator.appVersion.indexOf("KHTML") != -1) {

      // for KHTML browsers
      comet.connection = document.createElement('iframe');
      comet.connection.setAttribute('id',     'comet_iframe');
      comet.connection.setAttribute('src',    './backend.php');
      with (comet.connection.style) {
        position   = "absolute";
        left       = top   = "-100px";
        height     = width = "1px";
        visibility = "hidden";
      }
      document.body.appendChild(comet.connection);

    } else {
    
      // For other browser (Firefox...)
      comet.connection = document.createElement('iframe');
      comet.connection.setAttribute('id',     'comet_iframe');
      with (comet.connection.style) {
        left       = top   = "-100px";
        height     = width = "1px";
        visibility = "hidden";
        display    = 'none';
      }
      comet.iframediv = document.createElement('iframe');
      comet.iframediv.setAttribute('src', './backend.php');
      comet.connection.appendChild(comet.iframediv);
      document.body.appendChild(comet.connection);

    }
  },

  // this function will be called from backend.php  
  printServerTime: function (time) {
    $('content').innerHTML = time;
  },

  onUnload: function() {
    if (comet.connection) {
      comet.connection = false; // release the iframe to prevent problems with IE when reloading the page
    }
  }
}
Event.observe(window, "load",   comet.initialize);
Event.observe(window, "unload", comet.onUnload);
</script>

</body>
</html>

其次我们需要有自动连接的功能，当comet连接timeout时，

  window.onload = function() {
    var iframe = $("fullResponse");
    iframe.src = "reader.php";
    iframe.onload = disconnected;
    if (iframe.readyState) setTimeout("MS_checkiframe(), 500);
  }

  function disconnected() {
    // do whatever we normally do when we detect a disconnect
    $("fullResponse").src = "reader.php";
    if ($("fullResponse").readyState) setTimeout("MS_checkiframe(), 500);
  }

  function MS_checkiframe() {
    if ($("fullResponse").readyState=="complete") {
      disconnected();
    } else {
      setTimeout("MS_checkiframe()", 500);
    }
  }

最后是Tomcat comet servlet。

import org.apache.catalina.CometEvent;
import org.apache.catalina.CometProcessor;

import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.ArrayList;

/**
 * Created by IntelliJ IDEA.
 * User: Denny
 * Date: 2009-11-19
 * Time: 11:42:30
 * To change this template use File | Settings | File Templates.
 */
public class IECometServlet extends HttpServlet implements CometProcessor{

    public static ArrayList<HttpServletResponse> connections =
        new ArrayList<HttpServletResponse>();

    public void init() throws ServletException {

    }

    public void destroy() {
        connections.clear();

    }

    public void event(CometEvent event) throws IOException, ServletException {
        HttpServletRequest request = event.getHttpServletRequest();
        HttpServletResponse response = event.getHttpServletResponse();
        if (event.getEventType() == CometEvent.EventType.BEGIN) {
            event.setTimeout(Integer.MAX_VALUE);
            System.out.println("Begin for session: " + request.getSession(true).getId());
            PrintWriter writer = response.getWriter();
            writer.println("<!doctype html public \"-//w3c//dtd html 4.0 transitional//en\">");
            writer.println("<html><head><script type=\"text/javascript\">var comet = window.parent.comet;</script></head><body>");
            writer.print("<script type=\"text/javascript\">");
            writer.println("comet.printServerTime('Connection begin...');");
            writer.print("</script>");
            writer.flush();
            synchronized (connections) {
                connections.add(response);
            }
        } else if (event.getEventType() == CometEvent.EventType.ERROR) {
            System.out.println("Error for session: " + request.getSession(true).getId());
            synchronized(connections) {
                connections.remove(response);
            }
            event.close();
        } else if (event.getEventType() == CometEvent.EventType.END) {
            System.out.println("End for session: " + request.getSession(true).getId());
            synchronized(connections) {
                connections.remove(response);
            }
            PrintWriter writer = response.getWriter();
            writer.println("</body></html>");
            event.close();
        } else if (event.getEventType() == CometEvent.EventType.READ) {
                InputStream is = request.getInputStream();
            byte[] buf = new byte[512];
            do {
                System.out.println("Read for session: " + request.getSession(true).getId());
                int n = is.read(buf); //can throw an IOException
                if (n > 0) {
                    log("Read " + n + " bytes: " + new String(buf, 0, n)
                            + " for session: " + request.getSession(true).getId());
                } else if (n < 0) {
                    System.err.println("Impossible.");
                    return;
                }
            } while (is.available() > 0);
        }
    }
}

我们往response中写入javascript片段，这段javascript会在iframe中执行，然后在parent window中显示出来。

参考：http://ajaxpatterns.org/HTTP_Streaming#Detecting_a_disconnect
http://www.zeitoun.net/articles/comet_and_php/start

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2009-11-23 18:23
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1 楼 kellersoon 2010-09-10

// For other browser (Firefox...)  
      comet.connection = document.createElement('iframe');  
      comet.connection.setAttribute('id',     'comet_iframe');  
      with (comet.connection.style) {  
        left       = top   = "-100px";  
        height     = width = "1px";  
        visibility = "hidden";  
        display    = 'none';  
      }  
      comet.iframediv = document.createElement('iframe');  
      comet.iframediv.setAttribute('src', './backend.php');  
      comet.connection.appendChild(comet.iframediv);  
      document.body.appendChild(comet.connection);

在ff下依然有请求进度条，不知道你是怎么解决的，谢谢！

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