PushQueue Demo App

This application demonstrates the use of App Engine TaskQueue and its zero-code-change migration to Google Cloud Tasks using a forked SDK.

Features & What to Test

• Simple Task: Enqueue a simple task to the default queue.
• Task with Payload: Enqueue a task with a custom string payload.
• Delayed Task: Enqueue a task with a countdown delay (in seconds).
• Task to Custom Queue: Enqueue a task to a non-default queue (demo-queue).
• Task with Custom Header: Enqueue a task with a custom HTTP header.
• Batch Create Tasks: Enqueue multiple tasks in a single RPC call.
• Delete Task: Delete a specific task by name.
• Batch Delete Tasks: Delete multiple tasks by name.
• Fetch Queue Statistics: Retrieve stats like number of tasks and in-flight requests.
• List Tasks: List tasks in a queue (calls Cloud Tasks API directly).
• Task with Retry Options: Enqueue a task with custom retry limits.
• Transactional Task: Tasks added within a Datastore transaction are only dispatched upon successful commit. Supports simulated failure.
• Named Task: Enqueue a task with a specific name.
• Task with ETA: Enqueue a task with a specific execution time (ETA).
• Purge Queue: Remove all tasks from a specific queue.
• Task to Age Limit Queue: Enqueue a task to a queue with age limits configured.
• Async/Sync Methods: All operations support both synchronous and asynchronous execution.

Forked SDK for Cloud Task Routing

This app uses a custom-built version of the App Engine Java SDK (appengine-api-1.0-sdk). The SDK has been modified to intercept TaskQueue calls and transparently route them to Google Cloud Tasks when the environment variable GAE_PUSHQUEUE_BACKEND=CLOUD_TASK is set.

It also includes a Transactional Outbox pattern implementation:

• Tasks are stored in Datastore (_AE_PendingCloudTask) during a transaction.
• Dispatched to Cloud Tasks after commit.
• Includes an automatic sweeper servlet at /_ah/cloudtask/sweep for task recovery.

How to Run Locally (DevAppServer)

1. Build the SDK: (If not already built) Navigate to the SDK directory (/Users/gajjarc/Desktop/java-taskqueue/appengine-java-standard) and run:

   JAVA_HOME=/opt/homebrew/Cellar/openjdk/25.0.2/libexec/openjdk.jdk/Contents/Home ./mvnw clean install -DskipTests -Dmaven.javadoc.skip=true

2. Build the Demo App: Navigate to the pushqueue-demo directory and run:

   JAVA_HOME=/opt/homebrew/Cellar/openjdk/25.0.2/libexec/openjdk.jdk/Contents/Home ../appengine-java-standard/mvnw clean package

3. Run the Server: To run with Cloud Tasks enabled:

   GAE_PUSHQUEUE_BACKEND=CLOUD_TASK JAVA_HOME=/opt/homebrew/Cellar/openjdk/25.0.2/libexec/openjdk.jdk/Contents/Home ../appengine-java-standard/mvnw appengine:run

   To run with legacy TaskQueue:

   JAVA_HOME=/opt/homebrew/Cellar/openjdk/25.0.2/libexec/openjdk.jdk/Contents/Home ../appengine-java-standard/mvnw appengine:run

   (Note: You can also configure this in src/main/webapp/WEB-INF/appengine-web.xml)

How to Deploy

To deploy this application to production App Engine while supporting the forked SDK, run the following commands from the pushqueue-demo directory:

1. Package the application: Ensure the pom.xml points to the custom SDK version (e.g., 5.0.1-SNAPSHOT).

   ../appengine-java-standard/mvnw clean package

2. Deploy using Maven: Use the App Engine Maven plugin to deploy:

   ../appengine-java-standard/mvnw appengine:deploy

3. Ensure Environment Variables: Make sure GAE_PUSHQUEUE_BACKEND=CLOUD_TASK is set in your appengine-web.xml for production if you want to enable Cloud Tasks routing there.