Failed to deploy to Google App Engine because --use_java7 flag has not been set

Question

------------ Deploying frontend ------------

Preparing to deploy: Created staging directory at: \'C:\\Users\\ADMINI~1\\AppData\\Local\\Temp\\ap

Answer 1

The relevant system level property is shown here: com.google.apphosting.runtime.use_java7

It can be passed into appCfg.sh like so:

appcfg.sh --use_java7 update

Answer 2

As per the 1.7.3 blog post:

In an upcoming release, we will be including some of the new Java 7 functionality as well as formal Java 7 support within the App Engine Java runtime.

and...

And while Java 7 support is not yet available within the App Engine Java runtime, developers interested in an early preview can sign up for our trusted tester program.

You'll need to either be accepted into the TT program, or to wait for a future release where Java 7 works in production.