To migrate to the Java 11 runtime, your application must have a Main class that starts a web server. This sample is a shared artifact that provides a Main class to instantiate an HTTP server to run an embedded web application WAR file.

For more information on the Java 11 runtime, see Migrating your App Engine app from Java 8 to Java 11.

This sample is used as a dependency and must be installed locally:

mvn install

See helloworld-servlet for a complete example.

Your project's pom.xml needs to be updated accordingly:

• Add the appengine-simple-jetty-main dependency:

<dependency>
  <groupId>com.example.appengine.demo</groupId>
  <artifactId>simple-jetty-main</artifactId>
  <version>1</version>
  <scope>provided</scope>
</dependency>

• On deployment, the App Engine runtime uploads files located in ${build.directory}/appengine-staging. Add the maven-dependency-plugin to the build in order to copy dependencies to the correct folder:

<plugin>
  <groupId>org.apache.maven.plugins</groupId>
  <artifactId>maven-dependency-plugin</artifactId>
  <version>3.1.1</version>
  <executions>
    <execution>
      <id>copy</id>
      <phase>prepare-package</phase>
      <goals>
        <goal>copy-dependencies</goal>
      </goals>
      <configuration>
        <outputDirectory>
          ${project.build.directory}/appengine-staging
        </outputDirectory>
      </configuration>
    </execution>
  </executions>
</plugin>

To use the dependency, add the entrypoint to your app.yaml file. The entrypoint field will start the Jetty server and load your WAR file.

runtime: java11
entrypoint: 'java -cp "*" com.example.appengine.demo.jettymain.Main helloworld.war'

The [Exec Maven Plugin][exec-plugin] has been added so you can run your application locally. It is possible to use the Jetty Maven Plugin for rapid development and testing, but using the Exec Maven Plugin will ensure the provided server is running your application as expected.

• Start the server with your WAR file as an argument:

mvn exec:java -Dexec.args="../sample/target/sample.war"