This sample demonstrates migrating a WAR packaged servlet to Java 11. To migrate to the Java 11 runtime, your application must have a Main class that starts a web server. This sample is dependent on artifact appengine-simple-jetty-main to provide a Main class that starts an embedded Jetty server.

The pom.xml has been updated accordingly:

• Update maven compiler to use Java version 11:

<properties>
  <maven.compiler.source>11</maven.compiler.source>
  <maven.compiler.target>11</maven.compiler.target>
  <failOnMissingWebXml>false</failOnMissingWebXml>
</properties>

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

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

Note: this dependency needs to be installed locally.

• 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>

The appengine-web.xml file has been removed and an app.yaml has been added to manage your application settings:

• The entrypoint field will start the Jetty server and load your WAR file.

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

The exec-maven-plugin has been added to appengine-simple-jetty-main so you can run your application locally.

• Package your app:

mvn clean package

• Move into the directory:

cd ../appengine-simple-jetty-main

• Install the dependency:

mvn install

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

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

Then visit: http://localhost:8080/hello

While in the helloworld-servlet directory, use the appengine-maven-plugin to deploy your app:

mvn clean package appengine:deploy

Then visit: https://YOUR-PROJECT-ID.appspot.com/hello