I've been working on an application which can be deployed via Java Web Start. One nice think about Web Start is that it will use content negotiation with the server to download highly compressed jar files when they are available.

The documentation includes sample Servlet code to handle the negotiation, which is nice, but I didn't want to run a Servlet container just for this. Thankfully I ran across Keith Lea's blog entry Guide: How to use Pack200 for your Java Web Start applications on Apache Web Server which shows how to use Apache's own content negotiation modules and eliminates the need for any Servlets. However, it seemed like it could still be made a little simpler. In particular, I didn't like having to create a "type map" for each compressed jar. What follows is what I think is the simplest possible configuration for getting this to work on Apache 2.

Add the following to your global httpd.conf file:

AddType application/x-java-jnlp-file .jnlp
AddType application/x-java-archive .jar
<Files *.jar.gz>
  AddEncoding x-gzip .jar
  ForceType application/x-java-archive
</Files>
<Files *.jar.pack.gz>
  AddEncoding pack200-gzip .jar
  ForceType application/x-java-archive
</Files>

In each folder where you will serve jar files from, add an .htaccess file with these lines:

Options +MultiViews
MultiviewsMatch Any

That's it for configuration! Now you just have to drop the right jars into the folder with the .htaccess file. If your original jar is named foo.jar, you should put the following into the folder:

foo.jar.unpacked

original jar, just renamed

foo.jar.gz

gzipped

foo.jar.pack.gz

compressed with Pack200

For my application these three jars were 823, 698, and 234 kilobytes, respectively. Because Web Start auto-updates those bytes can really add up in saved bandwidth costs over time.

Here is a simple shell script which will take a single unpacked jar file and create the three necessary files:

#!/bin/sh
gzip -c $1 > $1.gz
pack200 $1.pack.gz $1
mv $1 $1.unpacked

Note that renaming foo.jar to foo.jar.unpacked is a critical step. The Apache MultiViews feature will disregard the compressed jars and always serve foo.jar if it actually exists. You don't have to use the .unpacked suffix, just make sure to tack on something.