I think the easiest way is to create a pipe in C++ to which the server would write the log and Java (via C++ JNI) would read it. My Android-educated colleague hinted me at this solution.
There is also a way to call Java stuff from a C++ thread, but it's not so easy (need to call AttachThread(), with a parameter that is received on library load via OnLoad...() ) and I think the pipe solution is much easier and cleaner.
There is also a way to call Java stuff from a C++ thread, but it's not so easy (need to call AttachThread(), with a parameter that is received on library load via OnLoad...() ) and I think the pipe solution is much easier and cleaner.