OK...thanks to qwerty I reckon I'm getting somewhere

[See attached .tar.gz]

I converted the Vala into a little C prog (main.c)

I included the service and desktop files

Now, when I click on a jarfile in FileManager it no longer asks me what I wish to use to open it with....it just does nothing.

So I ran the javalauncher prog on the cmd line, and I could see that it successfully called osso_initialize and osso_mime_set_cb, but I have no way of knowing if the prog is being successfully called by FileManager/mime_open.

What is the best way to debug this mechanism?