update Manifest in jar files

I want to update Manifest file in jar files (add new lines). Do i need to unpack the files change Manifest and pack it again or is there another way. I need to do it from java not from operating system.
[209 byte] By [logmana] at [2007-11-26 19:56:57]
# 1
> I want to update Manifest file in jar files (add new> lines). Do i need to unpack the files change Manifest> and pack it again Yes.
CeciNEstPasUnProgrammeura at 2007-7-9 22:51:25 > top of Java-index,Java Essentials,Java Programming...