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.
This sample displays what's going on in your app. It dumps the environment and lots more.
See the Google App Engine standard environment documentation for more detailed instructions.
Use either:
gcloud initgcloud auth application-default login
$ mvn appengine:run
$ mvn appengine:deploy
This small example application demonstrates the use of the App Engine Socket API to query a Whois server.
To build, install maven, then run mvn package.
You can run the local dev app server via mvn appengine:devserver and deploy via mvnappengine:update.