add google app engine sdk to gwt 2.8 project

I develop gwt project until now i used with google app engine and gwt 2.7 and everything is ok but i want to upgrade to gwt 2.8 and i can not. 

this is what i did until now i remove the google app engine sdk and installed the gwt plugin 3 include gwt 2.7 and gwt 2.8 and javascript debugger form this site http://gwt-plugins.github.io/documentation/gwt-eclipse-plugin/Download.html i removed the google app engine sdk because eclipse said me to remove it. i copied all packages from old project to new project. but i have errors because i removed google app engine sdk. I installed Google cloud paltform and i can create new project in google app engine but i cant add sdk to gwt project. how i can connect between google app engine and gwt 2.8 and deploy the project to google

in my code i get error like this "The import javax.jdo cannot be resolved for this line"

import javax.jdo.annotations.IdGeneratorStrategy;

I'm really lost all the week i work on upgrade my project to new gwt 2.8 thank you

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