I wrote a little bit here about my experiences with this sort of thing. There's not much you can do when this starts happening at a company. You can try to wait it out and hope that your PHB will leave or get fired, you can argue your case with a higher power (which will mark you as a troublemaker in the eyes of your PHB), you can go with it, or you can leave. If you don't feel that the decision is likely to get changed, my advice would be to try it out (i.e. give their decision a chance and see if it does make anything better) and then leave if you aren't having fun.

The strongest argument that manager types understand about this sort of thing is that it will cost a lot more to use Java. Potentially millions more when you account for commercial app servers, IDEs, extra hardware (commercial app servers tend to be very slow), and much longer development times. Open source Java tools can be an enjoyable experience, but the expensive commercial ones tend to be painful and slow. If you want to fight it, that's probably your best area of argument.