Jar Prune

Disclaimer

Please do not email me about this project without reading the disclaimer above.

Introduction

Various people have tried to write a replacement for jar.exe. The results have been disappointing. Attempts are buggy or they are not integrated into various building schemes such as Ant and Maven. Projects are abandoned leave users high and dry. Jar.exe, Maven and Gradle all include many more classes that are ever used. Basically Maven and Gradle include entire jars if even one class in the jar might be used. This causes distributables to bloat to several times the size they need be.

The Problem

There are four major problems with jar.exe:

1. It requires you to manually list all the class files and resources to include.
2. It will not warn you of missing class files.
3. It does not automatically exclude class files that are not really needed causing disbributables to bloat. Keeping distributable size down is especially important for Applets and Jawa Web Start.
4. It is slower than compilation.

The Solution

This project will help with (1), (2) and (3) but not (4). I suggest a much less ambitious project than others have attempted. I suggest a jar pruner. It examines a finished jar and chases the dependencies and produces a list of jar members that are not on the dependency tree. These may be:

• Unused classes
• Dynamically loaded classes
• Resources

It is up to the programmer to decide which classes fit in which categories and perhaps prune some classes from the lists given to jar.exe.

This simplifies the task of jar building. The programmer can throw the kitchen sink into the jar, then use jarpruner to shave it back prior to distribution. There is no need to shave it until the program is stable. Unused classes at an intermediate stage may be used later.

To implement this project, you don’t have to build manifests, digests or select which files to include. This makes for a much simpler coding task. You don’t have to parse any command files. Your program does not modify any files. It cannot do any serious damage.

Your input consists of a list of the key classes you load dynamically and the resources. The output consists a list of the classes that have to be present because they are either referenced, a list of classes indirectly referenced by dynamically loaded classes and a list of the orphans not referenced that may be safely removed. You use this information to create a slimmer manifest. If you chop too much or not enough, you will find out when you run jarprune on the slimmed jar. Everybody who posts a jar or the web or distributes one could make use of this utility. It is compatible as a final step of all build systems.

Further, it could warn you of indirectly referenced classes not present, saving you finding out later when in the course of some execution path the class is finally used.

Futures

After you have successfully tackled this project, you might try taking over the defunct GenJar project and debugging it and providing an ANT (A Neat Tool), standalone and Maven interface. Then your utility builds the jar without using jar.exe given just a list of resources and dynamically loaded classes. From dependencies, you can automatically include classes the dynanmically-loaded classes use.

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