Distributing Jython Apps in a Single JAR file

May 20, 2009 at 02:20 PM | categories: python, java | View Comments

I've been writing a lot of one-off type applications at work lately, which is always kind of a joy for me because these sorts of applications don't need to be maintained or supported in any way, which means I can write them however I want.

So I write them in Python :)

Jython allows me to interface with all the plethora of Java libraries that we use at work, and it lets me program in a language that not only I can tolerate, but one that I respect and love.

But even though these are one-off applications, they still need to be easy to use, and in some cases I won't even be the one running the application. I want these applications to just work damnit.

So, packaging my Jython application into a single executable jar file that contains all of the third party dependancies inside is my goal. I want to send the user the jar file, have them double click on it, and have it immediately start running. It can't get a whole lot easier than that.

The Jython wiki has a page about doing something along these lines. The recipe there called the Jar Method works quite well. The one drawback that it has is that all of the Java dependancies need to be exploded into the main jar root, which when you're dealing with dozens of jar dependancies, it can start to get tedious, messy, and in some cases will even violate the license of a particular library.

One-Jar is a special class loader that can load a jar file that is inside of another jar file, something that the regular class loader from Sun is incapable of doing. Using One-Jar lets my application reside inside of a jar file and contain all my dependancies as seperate jar files inside the main jar file.

I've created a sample project that shows how I normally create a new Jython project hosted inside a single jar file with One-Jar. You'll need the following tools to check out the project:

Check out the project like so:

 git clone git://github.com/EnigmaCurry/Single-JAR-Jython-Example.git

Build the project:

cd single-jar-jython-example


Run the example by double clicking it or via the command line:

 java -jar JythonExcelExample.jar

This is just a demonstration app, it doesn't do a whole lot, it outputs an excel file in the current directory listing some computer parts. The point of the application is to show how Jython can integrate with existing Java third-party libraries (in this case Apache POI.)

Instructions for basing your own application on this example are contained inside the README.txt file.

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