I found this question .jar to .cs class/file transform technique or utility? which also would solve my problem.
But since I should provide a tool which not only generates the C#-Code but also compiles it to one dll, and this would be easiear to do only in C#, is there any .net library with which I can reflect Classes and Interfaces which are stored in a jar file? I just need the signatures for the Methods, not to invoke it.
thx