使用htmlfile隐藏IE浏览器正在打开网页状态的代码
一般情况下，采用长连接，能持续的在客户端显示信息。
比如
<%@ page language="java" c pageEncoding="utf-8"%>
<%
out.flush();
int number = 0;
while (true) {
out.println(new java.util.Date()+"
");
out.flush();
Thread.sleep(100);
System.out.print(".");
if (number++ > 100) {
break;
}
}
%>
这个代码会在客户端连续的显示时间。请注意，浏览器的正在下载是一直在运行中的。这个会让客户感到疑惑，难道还有东西在运行吗？
下面的这个方法，可以解决这个问题
我们先看服务器端代码。
使用了prototype.js
<%@ page language="java" contentType="text/html; charset=utf-8" pageEncoding="utf-8"%>
<!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 php backend</title>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
</head>
<body>
<script type="text/javascript">
// KHTML browser don't share javascripts between iframes
var is_khtml = navigator.appName.match("Konqueror") || navigator.appVersion.match("KHTML");
if (is_khtml)
{
var prototypejs = document.createElement('script');
prototypejs.setAttribute('type','text/javascript');
prototypejs.setAttribute('src','../js/prototype.js');
var head = document.getElementsByTagName('head');
head[0].appendChild(prototypejs);
}
// load the comet object
var comet = window.parent.comet;
</script>
<%
out.flush();
int number = 0;
while (true) {
// 这里生成了调用js的代码
out.println("<script type='text/javascript'>comet.printServerTime('" + new java.util.Date() + "');</script>");
out.flush();
Thread.sleep(100);
// 控制台显示，程序正在运行，正式运行可去掉
System.out.print(".");
// 防止程序一直运行，给调试带来麻烦，正式运行可去掉
if (number++ > 100) {
break;
}
}
%>
关键在客户端代码
<%@ page language="java" contentType="text/html; charset=utf-8" pageEncoding="utf-8"%>
<!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="../js/prototype.js"></script>
</head>
<body>
<div id="content">The server time will be shown here</div>
<script type="text/javascript">
var url= 'testLinkData2.jsp';
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='./"+url+"'></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', './'+url);
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', './'+url);
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>
请注意其中的
comet.connection = new ActiveXObject("htmlfile");
部分，就是这段代码生成了一个可以在IE浏览器下面，不再显示正在下载状态。据说这个是google的聪明人发现并应用于google的gtalk和gmail
最后，我们来看使用Ajax的查询方式，
服务器端在没有数据的情况下会阻塞，直到有数据。
服务器端
<%@ page language="java" contentType="text/html; charset=utf-8" pageEncoding="utf-8"%>
<%
out.flush();
int number = 0;
while (true) {
// 这里可以插入检测的代码，我后面直接休眠100毫秒代替了
out.println("{'timestamp':'"+System.currentTimeMillis()+"','msg':'"+ new java.util.Date() + "'}");
out.flush();
Thread.sleep(100);
System.out.print(".");
if (number++ > 1) {
break;
}
break;
}
%>
看关键的客户端