Please note that a lot of folks do not have Java enabled in their web browser.
I strongly advise against this. Java Applets are a huge security hole, not to mention the negative reputation they have. Much better just to go with LibGDX. Code everything in Java and deploy to HTML5/JS, Android, iOS, PC, Mac, Linux and who knows what else.
I wrote the book on Java game programming, and even I say don't try this. Your time is better spent literally doing anything else.
Also, remember that if you're one or two people, you can make your own tech. But you can't just tell 50 people to go get to work while you make the engine. What are the artists, composers, and game designers going to use? They don't want to redo everything once the engine is done.