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 demonstrates how to use Cloud SQL on Google App Engine

Before you can run or deploy the sample, you will need to create a Cloud SQL instance)

1. Create a new user and database for the application. The easiest way to do this is via the Google Developers Console. Alternatively, you can use MySQL tools such as the command line client or workbench.
2. Change the root password (under Access Control) and / or create a new user / password.
3. Create a Database (under Databases) (or use MySQL with gcloud beta sql connect <instance> --user=root)
4. Note the Instance connection name under Overview > properties (It will look like project:instance for 1st Generation or project:region:zone for 2nd Generation)

or

gcloud sql instances describe <instance> | grep connectionName

$ mvn clean appengine:update -DINSTANCE_CONNECTION_NAME=instanceConnectionName -Duser=root
-Dpassword=myPassword -Ddatabase=myDatabase

Or you can update the properties in pom.xml

$ mvn clean appengine:devserver -DINSTANCE_CONNECTION_NAME=instanceConnectionName -Duser=root -Dpassword=myPassowrd -Ddatabase=myDatabase

Note - you must use a local mysql instance for the 1st Generation instance and change the local Url in src/main/webapp/WEB-INF/appengine-web.xml to use your local server.