如何创建兼容vaadin和app engine的eclipse项目

http://vaadin.com/wiki/-/wiki/Main/Google%20AppEngine%20HOWTO

尤其注意：

Note! There is a problem in the latest GAE plugin which prevents this from working. If you get an error like "The App Engine SDK 'C:\<workspace path>\<project name>\war' on the project's build path is not valid" do the following:

1. Open preferences -> Google -> App Engine and select the sdk version again
2. Open prefercense -> Java Build Path -> Export Order. Change the Export order so that the App Engine SDK is ABOVE the "Web App Libraries" classpath container.