How to shrink external java libs?

Question

I'm writing an applet, which uses ~10 external libraries. Together they occupy more than 2 megabytes. In some libs we use only 1-2 classes, so a lot of others can be safely deleted. So the question is how to remove unused classes from jar libraries?

A lot of other questions link to Proguard. But it doesn't process libraries (or I am doing something wrong) and also ruins parts of code which use reflection.

Answer 1

You could use the maven-shade-plugin and tell it to build a minimized jar file that combines your code and libs.

Answer 2

You could use something like ClassDep, which statically identifies which classes you will use.

However it's possible to easily fool this. Imagine some of your code contains:

Class.forName(className);

so you can dynamically build a classname and load that class. Tools like ClassDep can't identify these cases, so you'd need to perform comprehensive testing on your shrunken jars.

Answer 3

ProGuard can process your code together with the libraries (with the option -injars). You can still keep external libraries that you don't want to process (with the option -libraryjars).

Any automatic shrinking tool will have problems with reflection. ProGuard recognizes some basic reflection and it allows you to specify the parts of the internal API that should be preserved for the sake of reflection. ProGuard supports some powerful configuration, but depending on the amount of reflection in the libraries, it may still require trial and error.

Answer 4

You can simply "unzip" the JAR's, take only the classes you want from each, and place them in a custom archive. Brian A. gave a good suggestion on how to identify those classes and some caveats. I would add they you may be violating licenses as well...