How do I launch an application with a specific JDK? I'm on Sierra, and I have one legacy application that requests Java 6 to run. I have Java 7 installed, and I've also installed Java SE 6 from Apple, but I'm not sure how to force the application to use it.

When I launch it now, it does not launch properly, although the process seems to have started:

$ ps -ef | grep Java
501   572     1   0 11:29PM ??         0:04.63 /Applications/Memoir'44 Online.app/Contents/MacOS/JavaApplicationStub


There may be some subtleties with JavaApplicationStub and plists that I don't understand, but in any case the application never gets beyond initial startup (drawing a blank window), and does not function.
There's a support article from that game's developer addressing an issue where "the game freezes at start-up (blank screen)". It involves installing Java 1.6 (as you've done) and manually updating a library file, libjogl_awt.jnilib. However that article says the issue occurs when "[upgrading] to High Sierra", so this might not be what's causing your issue if you're still running Sierra.