Modifying a file inside a jar

I would like to modify a file inside my jar. Is it possible to do this without extracting and re jarring, from within my application?

File i want to modify are configuration files, mostly xml based.

The reason i am interested in not un jarring is that the application is wrapped with launch4j if i unjar it i can't create the .exe file again.

You can use the u option for jar

From the Java Tutorials:

jar uf jar-file input-file(s)

"Any files already in the archive having the same pathname as a file being added will be overwritten."

See Updating a JAR File.

Much better than making the whole jar all over again. Invoking this from within your program sounds possible too. Try Running Command Line in Java

You can use Vim:

vim my.jar

Vim is able to edit compressed text files, given you have unzip in your environment.

Java jar files are the same format as zip files - so if you have a zip file utility that would let you modify an archive, you have your foot in the door. Second problem is, if you want to recompile a class or something, you probably will just have to re-build the jar; but a text file or something (xml, for instance) should be easily enough modified.

As many have said, you can't change a file in a JAR without recanning the JAR. It's even worse with Launch4J, you have to rebuild the EXE once you change the JAR. So don't go this route.

It's generally bad idea to put configuration files in the JAR. Here is my suggestion. Search for your configuration file in some pre-determined locations (like home directory, \Program Files\ etc). If you find a configuration file, use it. Otherwise, use the one in the JAR as fallback. If you do this, you just need to write the configuration file in the pre-determined location and the program will pick it up.

Another benefit of this approach is that the modified configuration file doesn't get overwritten if you upgrade your software.