joustlog

Introduction

Lots of documentation exists about how to use Java 5’s new Pack200 JAR compression, with things like how to set up a Tomcat servlet to send its .pack.gz files with the right HTTP headers, and so on.

However, it is not clear how to use it in a more practical setting: an Apache web server. This weblog entry serves as a guide for how to get Pack200 working on Apache httpd. I don’t know if my method is the best way to do it, but it works. This method has been tested on Apache 1.3.31 and Apache 2.0.53.

UPDATE: I’ve updated the .htaccess file so it works on Apache 2.0 as well.

This guide assumes you have JAR files for your project’s classes (with extension .jar), and that you have Pack200-gzip-compressed versions (with extension .jar.pack.gz). If you don’t know how to compress your JAR files with Pack200, you can read more about Pack200 at Sun’s Java 5.0 documentation site. There is also a Pack200 Ant task, which makes it easier to integrate Pack200 compression into your build process.

Why you should use Pack200

Pack200 provides an insane amount of compression for your application’s JAR files. In my application’s case, Pack200+gzip compresses my 440KB jars to 89KB. This is an 80% improvement, saving my users 350KB worth of download time and bandwidth.

Your JNLP file

First, let’s talk about your JNLP file. The <resources> element should just reference your jars like you would normally:

<resources>
  <jar file="app.jar" />
</resources>

As you can see, your JNLP file doesn’t need to worry about Pack200; it will all be handled on the server side.

Apache server configuration

The Apache server’s configuration files are where all of the messy logic lies. In the folder where the JAR files will go, we must create an Apache .htaccess file, with these contents:

# Return the right mime type for JARs
AddType application/x-java-archive .jar
# Enable type maps
AddHandler application/x-type-map .var
Options +MultiViews
# Tweak MultiViews - this line is for
# APACHE 2.0 ONLY!
MultiViewsMatch Any

<Files *.pack.gz>
  # Enable the Content-Encoding header for .jar.pack.gz files
  AddEncoding pack200-gzip .jar
  # Stop mod_gzip from messing with the Content-Encoding
  # response for these files
  RemoveEncoding .gz
</Files>

Again, this file should be called “.htaccess” - don’t forget the dot at the front. The file should be placed in the folder which corresponds to the URL for the JAR files referenced in your JNLP file.

Alternatively, these lines could be placed in a <Directory> element inside your main httpd.conf file. However, you may not have access to this file on your web host, so .htaccess will suffice.

Type maps

Next, we must make a “type map file” for each jar file. (For more information about type maps, see Apache content negotiation documentation. This guide should be all you need to know for this purpose, however.)

For each JAR file, create a text file with the same name as the JAR file, but with “.var” at the end. For example, for “file.jar”, the type map filename would be “file.jar.var”. Inside the text file, write this:

URI: packed/file.jar.pack.gz
Content-Type: x-java-archive
Content-Encoding: pack200-gzip

URI: unpacked/file.jar
Content-Type: x-java-archive

(Replace “file.jar” in this example with the name of the JAR file this type map is for.) Repeat this process for each JAR file in your application, so you have a bunch of files all ending with “.jar.var”.

Folder structure

Next, we will set up the subfolders that contain the JARs and packed JARs. This part is simple: make two subfolders, one called “packed” and one called “unpacked”. Place all of your original JAR files (with extension .jar) in the “unpacked” folder, and all of your packed JARs (with extension .jar.pack.gz) in the “packed” folder.

Conclusion

Your file structure should now look something like this:

• myapp/
  • packed/
    • core.jar.pack.gz
    • ui.jar.pack.gz
  • unpacked/
    • core.jar
    • ui.jar
  • .htaccess
  • core.jar.var
  • myapp.jnlp
  • ui.jar.var

Now your server should be set up for serving your application’s JAR files to both Pack200-enabled Java 5.0 users, and to users of older versions of Java Web Start in regular JAR form. You can even visit yourserver.com/jarfolder/file.jar and see that the JAR file downloads just like it would without all this type map and Pack200 nonsense. However, when Java Web Start requests the JARs, it will receive a Pack200-compressed version.

This solution may not work for you for some reasons, but the most probable reason is that your web host has prevented you from using .htaccess files, or prevented you from using certain options (like type maps). If you can’t get it working, you may want to contact your web administrator.

If this solution doesn’t work for you, please let me know, either by email at keith@kano.net or by posting a comment below.

More information

• Apache type maps
• Pack200 compression and deployment
• Apache .htaccess files

This entry was posted on Saturday, October 16th, 2004 at 3:09 am and is filed under Code. You can follow any responses to this entry through the RSS 2.0 feed. You can skip to the end and leave a response. Pinging is currently not allowed.