Graceful shutdown in Spring Boot refers to gracefully stopping a running Spring Boot application, allowing it to complete its ongoing tasks and clean up resources before shutting down. It ensures that all active requests are processed or interrupted in a controlled manner, preventing abrupt termination.

During a graceful shutdown, Spring Boot initiates a sequence of steps to stop the application gracefully. These steps may include

1. Rejecting New Requests: The application stops accepting new requests, ensuring no new tasks are initiated.

2. Waiting for Active Requests to Complete: The application waits for the ongoing requests to finish processing. This allows the application to complete any pending tasks or operations.

3. Shutting Down Components Once all active requests are completed, the application shuts down its components, releasing resources, closing connections, and performing any necessary cleanup.

4. Notifying External Systems Optionally, the application may notify external systems, such as service registries or load balancers, to mark the application as unavailable during the shutdown process.

Graceful shutdown is critical when the application needs to perform cleanup tasks, release resources, or ensure data consistency. It helps prevent data loss, incomplete operations, or unexpected behavior during application shutdown.

Spring Boot provides mechanisms and hooks, such as the `ApplicationContext` events, `SmartLifecycle` interface, or custom shutdown hooks, to facilitate graceful application shutdown. These mechanisms allow developers to define custom behavior and perform necessary cleanup actions before the application terminates.