Creating patches for JAR file

[James Gordon]

Hi,
I have a JAR file project which need to be patched from time to time as we found bugs. The patch contains only the classes to fix the bugs.
I'm planning to have another utility program which:
1) extract the original JAR file to a location
2) scan through the new classes.
3) replace the new file to the extracted JAR
files location.
4) JAR back the amended folder.
Questions:
1) Are there any better ways to deal with this or
this is the only way? (It does look tedious)
2) Is there anyway to load the new JAR file
without restarting the app server, to achieve
zero down-time?

Please comments.
Thanks in advance.