I don't know Java, so I can't tell you the exact answer. But what I know about Java is that it requires a special kind of webserver: a java servlet server. Hiawatha a webserver, not a servlet server. So, you need Tomcat or some other kind of servlet server to run Java. Even Apache requires tomcat to run Java. But, like I said: I don't know Java. So I'm afraid I can't help you with that.
If Java somehow speaks CGI, you can use the 'CGIhandler' option to bind the .do extension to a Java parser. But that would be too easy. And since Java is complex and complicated, I guess that it won't work.
btw, I don't speak German. I speak Dutch, English, C and PHP