Could not load file/URL (file not found) error for JNLP file

Question

I am completely baffled in trying to figure out why I am getting the following error for some JNLP files but not others:
Error: could not load file/URL specified: C:\Users\tom\AppData\Local\Temp\javaws2
java.io.FileNotFoundException: C:\Users\tom\AppData\Local\Temp\javaws2 (The system cannot find the file specified)
at java.io.FileInputStream.open(Native Method)
at java.io.FileInputStream.<init>(Unknown Source)
at java.io.FileInputStream.<init>(Unknown Source)
at com.sun.javaws.jnl.LaunchDescFactory.buildDescriptor(Unknown Source)
at com.sun.javaws.Main.launchApp(Unknown Source)
at com.sun.javaws.Main.continueInSecureThread(Unknown Source)
at com.sun.javaws.Main$1.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)I have Googled around this forum and elsewhere, and have seen reports that this error is IE-specific, and seems to have something to do with no-cache headers being sent, or with the client browser's cache being full or turned off (which is not my case). I saw the information in the JavaWS FAQ, which recommended turning off security constraints for the JNLP's URI. I tried that, and it didn't help. One of the very baffling things is that I have created several variations of the JNLP file, with varying combinations of jars and property resources, and some combinations always work while other combinations never work. Here's an example:
<jnlp spec="1.0+" codebase="$$codebase">
   <information>
      <title>demo app</title>
      <description>illustrates weird bug</description>
   </information>
   <resources>
      <j2se version="1.5+"/>
      <jar href="randomFile.jar"/>
      <property name="xxx" value="xxxx"/>
      <property name="swing.metalTheme" value="steel"/>
   </resources>
</jnlp>The above file always fails with the error shown at the top of this message. However, if I remove either of the two properties, it works fine. And I have created other variations with lots of properties, some of which work. All of these variations are in the same directory in the war file, served by the exact same servlet (a slightly modified version of the jnlp.sample.servlet.JnlpDownloadServlet provided with JDK 1.6.0_3). Assuming that a no-cache header is the problem, what on earth could be causing some JNLP files to always be served with a no-cache header, while others are never served with a no-cache header?
On a related note, any recommended debugging techniques for seeing what headers are being transmitted? I tried adding a simple check for a "debug=true" parameter in the servlet that causes it to set the content type to "text/plain" instead of JNLP, and that allows me to see (rather than execute) the JNLP XML that's being returned, but it doesn't show me the HTTP headers that are being sent back. If any caching headers are being set, I think it must be being set by the servlet container itself, as it's nothing being set in the servlet code that I can see. So I don't see any way on the server side Java code to output or log the actual HTTP response (or is there?). Any tips in that regard much appreciated.
Edited by: TomC125468 on Aug 19, 2009 1:35 PM

Answer 1

Hi Luca-Sanna,
Thanks for the response. Re browsers, yes, it fails in IE but it succeeds in Firefox. The info on the JavaWS FAQ and other places all seem to indicate that it's an IE issue concerning handling of the cache-control headers.
I should check in my webserver forum (Sun WebServer 7) to see about logging options. Sniffing on the client side is not possible, as my app is required to use HTTPS exclusively, and unfortunately that also precludes a telnet GET request.