Its always best to use the jars, because you get the latest compiled code and its easy for the maintainers to maintain versions. But I think on the code branch the fix here is to decompile the jar using an open source decompiler like http://jd.benow.ca/ and then copy the code as is. Then you can see where the changes have been made.
DISCLAIMER
Please follow the licensing as the original wants it. I think its as per Apache, so make sure to include appropriate licensing information and credits and follow licensing laws.