I use a shared repository partly containing Java and Python code. The code basis mainly stands on python, but some libraries are written in Java.
Is there a possibility to parse or preprocess Java documentation in order to use it later in Python-Sphinx or even a plugin?
The javadoc command allows you to write and use your own doclet classes to generate documentation in whatever form you choose. The output doesn't need to be directly human-readable ... so there's nothing stopping you outputting in a Sphinx compatible format.
However, I couldn't find any existing doclet that does this specific job.
References:
UPDATE
The javasphinx extension may be a better alternative. It allows you to generate Sphinx documentation from javadoc comments embedded in Java source code.