jar built with jwrapper doesn't work

Question

jwrapper manipulates application jars somehow, and is resulting in a non-functioning jar: at runtime it throws a "MyClass cannot be cast to MyClass" type error. I believe this is caused by re-evaluating code that creates a class loader, leading to multiple instances of class MyClass being loaded.

The jwrapper docs don't describe the changes made to the jar, except for the use of pack200. I've tested pack200 in isolation, and it does not cause this problem.

I've also tested the jar built by jwrapper without using the wrapper executable, by passing it to "java -jar". So it's not jvm transmuting, or anything else that the wrapper is doing: the jar itself is broken.

UPDATE:

jwrapper allows skipping pack200, but then the install file is huge. Since pack200 works when run standalone, I could work around this if there were some way to tell jwrapper that the file is already packed. Using <Pack200Exceptions> doesn't help, because then it doesn't know the file is packed.

Answer 1

The underlying problem is that jwrapper sets the pack200 option "modification_time" to "latest", which changes the modification times of all the class files. At run-time this causes the clojure compiler to attempt to recompile the classes from source.

A work-around is to remove the .clj files from the jar prior to packaging, preventing the compiler from running. The lein ":omit-source" option is not sufficient here, because it leaves in .clj files from any dependencies. Instead you must use a pattern in :uberjar-exclusions, eg

:uberjar-exclusions [#".(clj|java)"]

as detailed here:

https://github.com/technomancy/leiningen/issues/1357