Play! Java web framework. How does their development server compile automatically?

Question

After looking at the Play! framework I find it really productive that the development server that it comes with automatically is able to compile .java files and show the changes, immediately. There's no hot deployer scanner that runs every tot seconds or so. The compilation happens when you hit refresh and it's extremely faster than my incremental mvn package. How do they do this?

I would like to know, well because I'm interested in knowing, but also because I don't want to use the entire Play! framework for my small project. I'm only interested in their development compilation process because I would like to adopt it :).

Any ideas?

Answer 1

I was reading about this just this morning. It actually takes your changed source files and uses the Eclipse Java Compiler (ECJ) internally before spitting out the compiled files to the built-in dev server.

The thing is, you probably don't want to go to the effort of wiring the ECJ into your "small project".

You can definitely approximate it though - the trick is to not do a mvn package, instead you want to be dropping the changed .class files into your webapp's exploded warfile directory on the filesystem.

If you're not tied to a particular app server/container, have a look at the Eclipse Jetty Plugin - looks like it's what you need, and Jetty is quick