there is nothing you must do to your existing code.  You might want to
recompile it, or run it through something like IntelliJ inspector to
convert loops to for:each, generify your Collections etc, but that is
optional.

As for your webserver, I don't recall having to do anything, or if it
was , it was just fixing one line in a config file somewhere. Just use
a global search utility like Funduc see
http://mindprod.com/jgloss/sr.html
to see if you can find the name of the old compiler burned into any
config file.

Make sure your new Javac.exe is on the path and the old one is not.
See http://mindprod.com/jgloss/jdk.html

Existing compiled classes should continue to run.

Existing source code should compile with -source 1.4 without
changes.

If you want to use the new features, then you may need to
make some changes to get it to compile (like if you have
been calling variables for enum).

Arne