Capturing speaker output in Java

I had a Java based app. that used Java Sound to tap into the sound flowing through the system to make a trace of it. It worked well on my own (Windows based) machine, but failed completely on some others.

It was determined that in order to get it working on those machines, would take nothing short of an audio loop-back in either software or hardware (e.g. connect a lead from the speaker 'out' jack to the microphone 'in' jack).

Since all I really wanted to do was plot the trace for music, and I figured how to play the target format (MP3) in Java, it became unnecessary to pursue the other option further.

(And I also heard that Java Sound on Mac. was horribly broken, but I never looked closely into it.)

Java is not the best tool when dealing with the OS. If you need/want to use it for this task, probably you will end using Java Native Interface (JNI), linking to libraries compiled in other languages (probably c/c++).