Java 7 runtime support on App Engine standard was deprecated on December 13, 2017 and will be shut down entirely on January 16, 2019. It is replaced by the Java 8 Runtime Environment.
Samples for the Java 8 runtime can be found here.
Shows the usage of the Namespaces API.
An App Engine guestbook using Java, Maven, and Objectify.
Data access using Objectify
Please ask questions on Stackoverflow
How do I, as a developer, start working on the project?
mvn clean appengine:devserver
mvn clean appengine:update -Dappengine.appId=PROJECT -Dappengine.version=VERSION