Jar file caching problem

Question

I'm running applets under IE in our application. The application contains multiple pages, each page with one applet. Each applet contains some shared jar file and one specific jar file for that applet.
Most of the time, the caching mechanism work fines. The browser is able to check with the HTTP server to see if any new jar files and download automatically. If no updates, the cached jars (in browser) are used.
However, at some other times, when I jump across several pages, performing different processing, suddenly the browser will reload all the jar files from the server. Even some shared jars are reloaded in every page within the same browser session.
If above problem occurs, I close the browser, open a new one and jumping to the pages again, the browser will be able to use the cached version again.
The runtime environment as follows:
JRE 1.3.1_02
IBM HTTP server 1.3.12.6
IBM WebSphere Appl Server 3.5.3
IE 5.50 (The "Check for newer versions of stored pages" is set to "Every visit to the page")
Pages created by JSP, syntax as follows:
<OBJECT classid="<%=JSPUtil.getClassid()%>" codebase="<%=JSPUtil.getPluginCodeBase()%>" WIDTH=100% HEIGHT=175% NAME=posApplet>
<PARAM NAME=ARCHIVE VALUE="<%=JSPUtil.getSharedArchives()%>, <%=JSPUtil.getArchiveLocation()+"/posPending.jar"%>">
<PARAM NAME=CODE VALUE=ho.aia.pos.pending.applet.PendingSGP >
<PARAM NAME=NAME VALUE="PendingRequirement" >
<PARAM NAME=codebase VALUE="<%=JSPUtil.getCodeBase()%>">
</OBJECT>
Do anyone knows anything about the problem?
Anyone knows how to make the caching work NORMALLY?
Thanks

Answer 1

Recently I tried to used some robot tools to test our application for performance issue. During the robot testing, I acceidentally discover some difference for the jar downloading which cause the above mentioned problem.
At first, this http request has no problem and the jar file is NOT downloaded. Http server shows a response code of "304", meaning download not required.
http_request
"GET lib/posLookup.jar HTTP/1.1\r\n"
"Accept: */*\r\n"
"Accept-Encoding: gzip, deflate\r\n"
"If-Modified-Since: Thu, 05 Dec 2002 17:22:12 GMT\r\n"
"User-Agent: Mozilla/4.0 (compatible; MSIE 5.5; Windows NT 4.0; T31246"
"1)\r\n"
"Host: defaulthost\r\n"
"Connection: Keep-Alive\r\n"
"Cookie: sesessionid=0001UULRZPFLU5IBRNBVHWUUAFI\r\n"
"\r\n";
Then after running for a while, the browser jumps into another page and finds that the same jar file "posLookup.jar" is required. It issue another http request to server as:
http_request
"GET lib/posLookup.jar HTTP/1.1\r\n"
"cookie: sesessionid=0001UULRZPFLU5IBRNBVHWUUAFI\r\n"
"User-Agent: Java1.3.1_02\r\n"
"Host: defaulthost\r\n"
"Accept: text/html, image/gif, image/jpeg, *; q=.2, */*; q=.2\r\n"
"Connection: keep-alive\r\n"
"\r\n";
But this time the user agent becomes Java1.3.1_02 and the accept type becomes text/html instead of original zip format. After this, I check the IE temporary file and found that the posLookup.jar is having a type of "HTML Document" instead of "Executable jar file".
Does anyone know whether this is a bug of the Internet Explorer or it is bug of the Java Plugin?
Appreciate any opinions or comments.
Thanks