RetryScheduler (Java)

A simple task retry scheduler to demonstrate the first principles of a robust retry system. Built using Java concurrency primitives.
This project simulates a retry mechanism that retries failed tasks using thread-safe queues and a scheduled retry loop (in a production-grade retry system, a persistent retry queue is preferred to an in-memory queue).

🚀 Project Overview

This project demonstrates the first principles of implementing a retry system in core Java using:

• BlockingQueue to buffer failed tasks
• ScheduledExecutorService a dedicated thread to periodically poll the queue
• ExecutorService to retry tasks using worker threads
• A shutdown hook: a dedicated thread that gracefully terminates the threads
• Retry logic that adds persistently failing tasks to a Dead letter Queue after 3 failed attempts.
• Exponential Backoff to avoid overloading the retry system

Each task has a retry count and is either:

• Re-queued on failure (up to 3 times)
• Redirected to a Dead Letter Queue (DLQ) after max retries

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🛠 Technologies Used

Tool	Description
Java 21+	Language for core logic
Maven	Build automation and dependency management
java.util.logging	Logging (default is java.util.logging)

✅ No third-party libraries required — pure Java!

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⚙️ How It Works

1. Tasks are simulated via doTask(task).
2. These are placed into a LinkedBlockingQueue.
3. A scheduled task polls this queue every 10 seconds.
4. If a task is present, it's submitted to a thread pool for execution.
5. If the task fails, it's retried up to 3 times.
6. After 3 failed retries, the task is logged as permanently failed.

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▶️ How to Run the Project

✅ Prerequisites

• Java 21 or higher
• Maven 3.x

📦 Build with Maven

mvn clean install

🚀 Run the Application

You can run the main class using maven (if you have maven installed):

mvn exec:java -Dexec.mainClass="org.emjay.task_retry.RetryApplication"

Or run using your IDE run configuration