Yes, it is possible to mix Java and Scala in a Play application. You can mix both Java and Scala controllers and Groovy and Scala templates. The instructions below have been tested on Play! 1.2.2RC1.
I would start by storing both Java and Scala controllers in app/controllers . Java, of course, is limited to one class for each file, but in Scala packages are not tied to files and directories, so you can give your Scala file any name; if you declare the package correctly, like
package controllers
Play should not have found them.
Scala templates should end with .scala.html and Groovy templates in regular .html . In the Scala controller, you create Scala templates with the html.templatename and Groovy templates with the Template("templatename").
I have never tried displaying a Scala pattern from a Java controller, but I do not understand why this should not be possible.
Finally, here's a useful reminder of Scala / Java interop .