I'm not an expert on this but as far as I know...

I would like to create a VST plug-in for my application. First, I saw
that most of the plug-in act like a black box and apply transformation
to the sound but what I would like to do is to Trigger a specific
sound my self. Is this possible with VST ?

A plugin does as you say having limited communication with the application.
You have to write the plugin to a predefined Steinberg interface that gets
passed (among other things) pointers to an input and output stream in a
method called "Process". It may not be relevant but a VST (or DX) plugin has
no synchronisation with the application. i.e. it never knows what time it
is. I think perhaps a VST instrument (a separate API) would allow you to do
what you say as they allow you to play sounds from Hard Disk (and memory)
from midi commands. Some guys over at alt.steinberg.cubase that
professionally develop may know the ins and outs.


Second : My Java module will send theses pluses information via socket
to the plug-in. Can a plug-in make low level communication with
another out-of-process application ?

Not sure about this one. I would immediately think know, but then two VST
instruments come to mind (Absynth and Fruity Loops VSTi) that start a mother
application outside Cubase as well as a VST instrument interface within
Cubase and both do communicate being interdependent on each other.

Hope this sends you on the right path. I'd be interested to know what books
you have read on Java Media programming as I'd love to get more into the
media APIs. Most of the books I've seen were written years ago!

regards,

Martin