Suppose you are in $JBOSSHOME/bin dir, your dev java files
are in ~<your_name>/someproject, also suppose that
jetty temp dir is in $JBOSSHOME/<jetty_tmp> dir.
Suppose you are changing file ~<your_name>/some/project/web/somedir/foo.jsp
to immediately force jasper recompilation, just do
(remember you are in $JBOSSHOME/bin dir)
cp ~<your_name>/some/project/somedir/foo.jsp ../<jetty_tmp>/Jetty_0_0_0_0_<your_port_number>__<your_web_appName>/webapp/somedir/.
That should do the trick.
But I am using Jboss3.0.3 with Tomcat 4.1.12