Been through the comment threads seen the common theme of Vaadin not working on Helios with GAE or not working in GAE in general. My question is if Vaadin is based on GWT technology, why is it so damn hard to to get the thing to play nice with Google App Engine without spitting null pointer exceptions all over the place? Just getting a little frustrated with all the these solutions online and yet even after trying those solutions nothing seems to work. And no the Vaadin GAE online help does not seem to work on Helios. It simply does not make sense that Vaadin based on GWT technology seems to like any and every other container/app server except GAE? It’s like you guys built a Ferrari but absolutely insist that your clients use BMW parts for maintenance and upkeep.
In general - GWT and Vaadin are quite different beasts. With GWT you can select if you want to store stuff in server-side session. In general most of the state will be stored on client-side and server-side session is kept really small. In Vaadin everything is stored on server-side state. For most deployment environments storing stuff in server-side state is ok. GAE has a nasty limitation - it wants to serialize server-side state for each request. This adds a bit of overhead for Google servers to handle. In principal this is Googles headache (they are paying for that extra CPU time), but in practice will add a bit of extra latency. I really hope that GAE will add support for at least “short-time” sticky sessions to be able to support stateful frameworks faster, better.
That said, NPE:s might not have anything to do with Vaadin or the session size. Please add some detail to make it possible to help you with NPE.
As for Helios and the Vaadin and GAE plugins, this probably needs some more investigation.
Many of the issues in the past have stemmed from the fact that the GAE plugin does not use a standard faceted Eclipse project type with the Dynamic Web Module facet, nor do GAE and the plugin use a standard directory layout. The project structure is non-standard with respect to common practices in servlet development, Eclipse web projects and Maven standard practices, so Vaadin is far from being the only project that suffers from this.
Also, the unavailability of the Google plugin source code does not make this any easier to resolve cleanly, and the Vaadin plugin should not depend on the GAE plugin being installed.
I take back what I said previously, it looks like the culprit to this whole frustration was my workspace. The workspace was previously used by JBoss Developer Studio IDE. It look’s like either the workspace was 1. corrupted somehow or 2. There are some conflicting plugins still left over from JBoss Developer Studio that is screwing up how Vaadin compiles the widgets. After moving to a new workspace I no longer have any compilation/deployment issues with Helios + Vaadin + GAE.