Mixing Java and Scala is almost seamless. We use WebWork/Struts2 (Java), and all our new Actions are written in Scala. We use Guice(Java) to inject objects in

Mixing Java and Scala is almost seamless. We use WebWork/Struts2 (Java), and all our new Actions are written in Scala. We use Guice(Java) to inject objects into Scala. Thrift also plays nicely with Scala. Two things that are a bit weird is that we can't use constructor injection w/ Guice, so we have to resort to the following ugly hack: @Inject var authenticationService: AuthenticationService = null; We haven't figured out how to construct a Tuple in Java. So if you have a Scala trait and want to implement it in Java, make sure you don't have use a Tuple return type.