Get source code of any class from within a Java program

Question

I'm attempting to retrieve the source code of any class (if available) from within a Java program for debugging purposes. Let's say I have the Class[_]'s reference to which I would like to retrieve the source code.

What I have attempted so far - in Scala:

val clazz = classOf[ClassDefinedInSeparateFile]

1. clazz.getProtectionDomain.getCodeSource.getLocation.toString + "/" + clazz.getPackage.getName.replaceAll("\\.","/") + "/" + clazz.getSimpleName + ".scala" - looks OK, the JAR is there and contains the .scala file, but could not open using Source.fromFile(...).
2. "/" + clazz.getPackage.getName.replaceAll("\\.","/") + "/" + clazz.getSimpleName + ".scala" - looks OK, but could not open using Source.fromInputStream(...)

Remarks:

• There is no IDE available in production or staging environments.
• In our setting JARs contain the source code .java or .scala files, therefore a decompiler is not necessary. (At least for the source code of the application, but not the dependencies. If a snippet is accessible of the application source code, that is enough - most exceptions are caught at the application level and relevant there.)

Thanks.

Answer 1

If the source is inside the jar, which is in classpath, you need to find out where it is exactly.

clazz.getName.replaceAll("\\.", "/") + ".scala" is an ok guess, but: (1) source code may not be in the same place as the classes - there could be a prefix (like src/ or whatever), or it could even be in a different jar, and (2) scala classes do not have to be in files with the same name - you can have several classes in one file, the file can be called foo.scala, some classes are generated on the fly etc. Also, a package is not always a directory in scala (it could be a package object for instance).

If you know the location inside the jar (and the jar is in the classpath), the way to open it is: clazz.getClassLoader.getResourceAsStream ... but, like I said above, the trick is to figure out the location. It is not easy (and there is no single standard way to do it).

Your best bet is indeed to use an IDE. I understand that you don't have it available in production environment, but you don't really need that. What you need is the production source code available on some machine where you have an IDE, and that you can achieve with a simple scp command.