Hi team,

I'm currently reviewing this pull request and will provide my feedback shortly. In the meantime, here's a summary of the changes for you and other reviewers to get up to speed quickly:

This pull request updates the Java version in the App Engine Qwik Start sample to Java 21. The changes are focused on theappengine-java21/helloworld/http-server directory.

Intent:

The primary goal is to modernize the sample application by using the latest Java version, improving compatibility and potentially leveraging new features.

Changes:

• Theapp.yaml file was updated to specifyruntime: java21. (Line 16 ofappengine-java21/helloworld/http-server/src/main/appengine/app.yaml)
• A newREADME.md file was added to provide instructions for deploying the updated application. (File:appengine-java21/helloworld/http-server/README.md)
• Thepom.xml file was updated to reflect the Java 21 runtime. (File:appengine-java21/helloworld/http-server/pom.xml)
• The main application file (Main.java) remains largely unchanged, demonstrating a simple HTTP server. (File:appengine-java21/helloworld/http-server/src/main/java/com/example/appengine/Main.java)

Activity:

The pull request references Buganizer issuehttp://b/393352626, suggesting this is part of a larger effort to update App Engine samples.

I'll provide a more detailed review shortly. Thanks!

And now, a little haiku to brighten your day:

Java twenty-one,
Code compiles, a clean deploy,
Happy coding now!

This pull request updates the Java version to Java 21 in the App Engine sample application. The changes include updatingapp.yaml, adding apom.xml for Maven build management, and creating aREADME.md file with instructions. The implementation looks good overall, and the added documentation is helpful. Here are a few minor suggestions:

Summary of Google Java Style Guide elements referenced:

• Comments: Documented using Javadoc style.
• Naming: Used descriptive names for classes and variables.