About a year ago, the ZeroTurnaround team decided to support the Scala community by providing a free license of JavaRebel to all Scala users. JavaRebel is a developer tool that alleviates the need to restart a JVM during development: As a developer recompiles some Java or Scala classes, JavaRebel notices the changed classes and reloads them to the currently running JVM. The result is that the code changes immediately become visible. That provides an experience Ruby and Rails developers are used to: After changing a Ruby or Rails class, one only has to reload the current browser window to see the effects of the changes.

Because JavaRebel works at the level of Java class files, it can be used for developing Scala code as well. ZeroTurnaound provides documentation on how to configure their tool to work with the major IDEs as well as application servers.

Over the last year, JavaRebel has evolved to be able to notice changes not only to recompiled classes, but to other code artifacts as well, such as configuration files of major application frameworks.

Building on JavaRebel's ability to seamlessly reload the effects of changes to all sorts of code implements, JavaRebel has evolved in production environments as well. In a production environment, such as a mission-critical app server, JavaRebel can reload a running Web application without requiring a server restart. Although some app servers, such as Glassfish, provide similar functionality, JavaRebel performs such reloading at a fine-grained level: instead of reloading an entire Web application, it can selectively replace only modified elements of a Web application's files.

At least year's Scala Liftoff meeting in San Francisco, ZeroTurnaround announced its support of the Scala community by providing free JavaRebel licenses to any Scala developer. The licenses provided at that time have expired but ZeroTurnaround wants to continue its support. Instead of a license that expires on a set date, you can now get a license with your name on it that lasts a full year. After that time, you an re-apply, and will receive a new license key. Scala developers can obtain a license key to JavaRebel at http://www.zeroturnaround.com/scala-license/

For Lift developers, the free Scala version of JavaRebel is already included in the Lift Installer. You still need to pick up a license key to activate it. Lift developers may also find it helpful that JavaRebel 2.0.2 fixed issues with nested expressions that came up on the Scala/Lift forums recently.

Finally, JavaRebel has made a name for itself in the past year and, as a result, got into a situation where a new name is now sought. More details about the name change are available in a recent blog post.

What do you think about JavaRebel's ability to improve the development experience? How do you think it compares with recent features of app servers to facilitate automatic reload of a Web application?