I am beginer too. After two months, investigating everything by myself, i found this forum. I am making my first project and i had the same troubles when building a project using the wizard from Elcipse->File->new-> GWTP Project.
I could run this as maven appengine:devserver but i couldn't foce it to show in Eclipse project menu Run As -> Web Application.
I have tried almost everything, changed in eclipse, changed pom, nothing worked
Try to do this my way. Run as maven build, and in launch configuration window, set Goals: appengine:devserver. It works simmilar, but u have to manualy copy adresses of devserwer to browser (dont have DevMode tab).
Of course, you can build a project using one of ArcBees maven archetypes, and then there is menu Run As -> Web Application (after u set correct options in web toolkit settings).
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Waldemar