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Creating a demanding application for a mass of people
my client wants a really demanding and scalable application. Can Vaadin handle many thousands requests at the same time or is it up to the business logic and server side technology? (I'm planning to use GAE because normal servers wouldn't just handle the amount of data being sent and received - clusterizing the servers would cost too much)
Is there a possibility to output raw html output (for phones) rather than AJAX / JS stuff?
This app requires having a lot of different front ends.
Can I use different languages and output them properly? Arabic, Russian, Chinese and other non latin languages.
Vaadin should not add any particular complexity, so the scalability is largely up to the server and the business logic. The default container implementations have some nonlinear complexity. There is some memory and time overhead, of course, and the UI state does take some memory as well. The UI memory consumption per application session can be significant if you have a large number of concurrent sessions, so you need to estimate the requirements. See the discussion in 18082 and 79720 for example.
There is no HTML mode any more. There was (and is) support in IT Mill Toolkit 4, the two-year old predecessor. You can get it from the download site, it's open source and IT Mill of course supports it for customers. Raw HTML of course has a lot of limitations.
You should be able to output any languages, just as in any HTML. There is no particular support for right-to-left languages, so you would have to implement that in your application logic.
as Marco previously said, the scalability is more up to the server-side technology, clustering, etc. Of course, when planning clustering you might to tweak your application server side code accordingly.
There are no international problems with Vaadin, we're using it successfully for multi-language applications with mix of latin and non-latin characters (English, Russian and Chinese)