As others have said, GWT is a very good option. To summarize:
- fast, very portable code using delayed binding; it only downloads code that runs in the user's browser, and only loads functions that are actually called; also, they are compressed
- reliability ; very few known problems.
- simplified debugging using the Java IDE; you can also look at un-obfuscated javascript if you want, but it seems (based on some reports that I saw and personal experience) that you basically never need this.
- support for a good library , including a beautiful built-in javascript interface, the ability to use existing Java libraries, and special support for ajax / rpc calls
- extensible and stylistically flexible ; you can customize all styles with your own css rules and extend your Widget base with your own Java subclasses.
So, I humbly disagree with the dominance that the results are ugly, as the encoder should “muffle” the basic functionality with its own CSS rules and other decorations. It would be the same mistake to call HTML “ugly” - if you do not try hard, it is ugly, but the strength and flexibility are in the hands of the encoder.
Oh, and this is also open source.