We’re big fans of Zero Turnaround’s JRebel product and we thought we should tell you all about it. We’re not in any way affiliated with the vendor, we’re just happy users.

For those of you who don’t know about JRebel it’s a JVM agent that allows developers to change code on the fly without needing to rebuild and redeploy their apps. Sounds like hotswap? well actually it’s much more advanced than traditional jvm hot swap because it allows you to modify the structure of classes on the fly so you can add and remove methods, fields etc. It also has some neat plugins like the spring plugin which lets us add beans on the fly (hot swap definitely won’t let you do that!)

We’ve found that fast turnaround really helps us to improve the quality of our code. Take this scenario … you want to test a small change (e.g. adding a field to a JSP) but every time you change something it take 2 mins for your app to start up. What happens? you don’t make and test changes in isolation because it’s too painful so you end up changing lots of stuff and hope it all works!

The tool not only allows us to be more productive, it also brings a little bit of happiness into our day … there’s nothing more frustrating that waiting for your app server to restart.

Give it a go … you may be surprised!