At least in Vaadin 7.3.x and 7.4.x, running on Tomcat with Push enabled, you may see several exceptions in your console having to do with Jetty. Even though you’re not using Jetty, this is happening because Vaadin is getting tricked into assuming that Jetty is being used, since a Jetty library is found in the Java classpath.
Vaadin does realize after the exceptions that Jetty isn’t actually there and continues gracefully. But though these exceptions are harmless, they’re still unsettling to constantly in your tomcat logs. As I mentioned, this is happening because there is some Jetty library in your Java classpath. So thus the obvious solution get to rid of these exceptions is to remove all Jetty libraries from your Java classpath. Search for any .jar’s that have “jetty” in the name, and remove them.
If you’re using Ivy or Maven dependency management, the library may be downloaded as a sub-dependency from another dependency. You will need to go through all your dependencies to check which ones also reference Jetty. The culprits in our case were vaadin-client-compiler and HtmlUnit (both reference Jetty for Jetty related things, but since we’re not using Jetty anyway, getting rid of the Jetty library should cause no harm).
We use Ivy, and I found how to exclude certain sub-dependencies, which is simple. Use the tag in your ivy.xml wherever jetty is a sub-dependency. A example follows:
<exclude org="org.eclipse.jetty" name="*" />
And viola! No more random Jetty based exceptions from Vaadin.