App Engine Java Guestbook

Copyright (C) 2010-2023 Google Inc.

Original Google App Engine Java sample, created in 2009, supporting Google App Engine Standard with Java8, Java11, Java17, and Java21 using Bundled Services like App Engine Datastore API,and App Engine Users API. By changine the field in the appengine-web.xml, you can select with Java version to use to execute this Java EE Web App, using Servlet and JSP. It demonstrates that code written back in 2009 with Google App Engine can still serve today with different JVMs.

Prerequisites

Download Maven

These samples use the Apache Maven build system. Before getting started, be sure to download and install it. When you use Maven as described here, it will automatically download the needed client libraries.

Create a Project in the Google Cloud Platform Console

If you haven't already created a project, create one now. Projects enable you to manage all Google Cloud Platform resources for your app, including deployment, access control, billing, and services.

1. Open the Cloud Platform Console.
2. In the drop-down menu at the top, select Create a project.
3. Give your project a name.
4. Make a note of the project ID, which might be different from the project name. The project ID is used in commands and in configurations.

Setup

Use either:

• gcloud init
• gcloud auth application-default login

Google Cloud Shell, Open JDK 17 setup:

To switch to an Open JDK 11 in a Cloud shell session, you can use:

   sudo update-alternatives --config java
   # And select the usr/lib/jvm/java-17-openjdk-amd64/bin/java version.
   # Also, set the JAVA_HOME variable for Maven to pick the correct JDK:
   export JAVA_HOME=/usr/lib/jvm/java-17-openjdk-amd64

Development differences between App Engine Java8 and Java11/17/21 Bundled Services

The only difference between a Java8 application and a Java11/Java17 application is in the appengine-web.xml file where you need to define the Java11/17 runtime and declare you need the App Engine APIs:

<appengine-web-app xmlns="http://appengine.google.com/ns/1.0">
    <runtime>java17</runtime> <!-- or java11-->
    <app-engine-apis>true</app-engine-apis>
</appengine-web-app>

For a Java21 usage with the new jakarta.servlet API, you need to define the Java21 runtime, declare you need the App Engine APIs:

<appengine-web-app xmlns="http://appengine.google.com/ns/1.0">
    <runtime>java21</runtime>
    <app-engine-apis>true</app-engine-apis>
    <system-properties>
        <property name="java.util.logging.config.file" value="WEB-INF/logging.properties"/>
    </system-properties>
</appengine-web-app>

For a Java21 usage with the ancient javax.servlet API, you need to define the Java21 runtime, declare you need the App Engine APIs and a new system property to stay with javax.servlet apis:

<appengine-web-app xmlns="http://appengine.google.com/ns/1.0">
    <runtime>java21</runtime>
    <app-engine-apis>true</app-engine-apis>
    <system-properties>
        <property name="java.util.logging.config.file" value="WEB-INF/logging.properties"/>
        <property name="appegine.use.EE8" value="true"/>
    </system-properties>
</appengine-web-app>

Everything else should remain the same in terms of App Engine APIs access, WAR project packaging, and deployment. This way, it should be easy to migrate your existing GAE Java8 applications to GAE Java11 or Java17 or Java21.

Maven

Running locally

    mvn appengine:run

Deploying

    mvn clean package appengine:deploy  -Ddeploy.projectId=XXXX