I am not able to figure out how to export a runnable jar in eclipse.

I have a java project (project A) (written by someone else) which when imported in Eclipse, I can click Build Project and it will create a projectName.jar file under bin/ directory. That jar file contains binary *.class files.

This jar file is added as external library for another java project (project B) which I want to debug. But because all the class files are binary I'm not able to do line-by-line debugging.

I tried exporting Runnable Jar in Eclipse, for that I have to select a Launch Configuration. But there is no main class in project A. (I recursively grepped for main and didn't find any).

What can I do to export jar of project A that contains respective source code also (which will be used in line-by-line debugging)?