Question

I need to patch a system in production however I have already change the main trunck in CVS. Since there are a lot of changes I do not want to revert the code to a previous version as there is only one class involve.

Could this be done ?

1. Stop the application.
2. Safely replace a edited *.class into an existing jar.
3. Re-start the application.

Many Thanks

Answer 1

Unless the jars are signed by someone else, it can be done. Jar files are just zip files after all, you unzip them, replace the file and zip them up again. If the jars are signed and you have the key, you have to sign the new jar again. (The jar command is the preferred way to do this.)

However it’s very bad practice to do this. Trust me, the amount of work you save now will be lost a hundredfold if this way of deploying becomes a habit. Unless there’s a real crisis (your application doesn’t even run or crashes every ten minutes for example), you should never ever do this.

If you use CVS, you should always tag your releases, but even if you haven’t done that, you can check out the trunk as it was on the release date, create a branch from there, apply the change to the branch and rebuild your application.

It takes about ten minutes (plus compilation time) and it’s a safe and proper method. You can launch the patched application in your test environment, test that it works and only deploy it afterwards.

Dropping a pre-compiled class file in an existing application can break the code in subtle ways that don’t become apparent until several days later. Recompiling and retesting the application takes this risk away, leaving just the much smaller risk associated with any code change.