Any decent Java IDEs can do this for you. I'm not sure if that capability covers Scala.

You can set a breakpoint (conditional or not), and have every thing within that context available for you. The next step is to launch an "Evaluation window" where you can execute Java code.

If you were to set the breakpoint at the web-application level (as opposed to plain Java process/class/console-app), you can get information of the Threads and Frames as well.

This techniques have been available for quite some time in the IDEs... that is provided you're not allergic to IntelliJ/NetBeans/Eclipse.

Best part: no code change.

I have no comment for those who prefer VIM/Emacs and bemoaned the lack of powerful stuff they got from other environments.