hotelapp-dev-2-optimistic-lock

[yennanliu]

No description provided.

[gemini-code-assist]

Summary of Changes

Hello @yennanliu, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly enhances the application's robustness by integrating optimistic locking across key entities. This prevents race conditions and ensures data consistency when multiple users attempt to modify the same resource simultaneously, leading to a more reliable and predictable user experience.

Highlights

• Optimistic Locking Implementation: Introduced optimistic locking to the Booking and Room entities by adding a @Version field, ensuring data integrity during concurrent updates.
• Global Exception Handling: Added a new GlobalExceptionHandler to gracefully manage OptimisticLockException and ObjectOptimisticLockingFailureException, providing user-friendly error messages for concurrent modification conflicts.
• Frontend Conflict Resolution: Updated the index.html to handle 409 Conflict responses from the backend, displaying appropriate messages and refreshing UI components to reflect the latest data state.
• Concurrency Testing Setup: Included H2 database dependency and new test configurations (application-test.properties) to facilitate robust testing of optimistic locking mechanisms.
• Dedicated Optimistic Locking Tests: Implemented OptimisticLockingTest to thoroughly verify the optimistic locking behavior for room bookings and updates under concurrent conditions.

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[gemini-code-assist]

Code Review

This pull request effectively implements optimistic locking to prevent race conditions during booking and other updates. The changes span the data entities, exception handling, frontend, and include comprehensive tests. The approach is solid. I have a few suggestions to improve consistency, security, and test robustness.

[gemini-code-assist]

This generic RuntimeException handler has two issues:

1. It returns 400 Bad Request for all runtime exceptions. Many runtime exceptions (like NullPointerException) indicate a server-side bug and should result in a 500 Internal Server Error.
2. It exposes the raw exception message (e.getMessage()) to the client. This can be a security risk as it might leak sensitive information about the application's internal workings.

It's better to return a generic error message for 500 errors and log the full exception details on the server for debugging.

    @ExceptionHandler(RuntimeException.class)
    public ResponseEntity<HotelController.ErrorResponse> handleRuntimeException(RuntimeException e) {
        // Log the exception here for debugging, e.g., using log.error("Unhandled exception", e);
        return ResponseEntity.status(HttpStatus.INTERNAL_SERVER_ERROR)
                .body(new HotelController.ErrorResponse("An unexpected internal error occurred."));
    }

[gemini-code-assist]

For consistency with other JPA annotations like @Entity and @Table used in this class, it's better to use jakarta.persistence.Version instead of org.springframework.data.annotation.Version. While Spring Data's @Version is designed for non-JPA data stores, using the standard JPA annotation directly makes the dependency on JPA more explicit and consistent throughout your JPA entities.

Suggested change

	import org.springframework.data.annotation.Version;
	import jakarta.persistence.Version;

[gemini-code-assist]

It's a good practice to log exceptions on the server side for debugging and monitoring purposes. The handleOptimisticLockException method currently swallows the exception details as the parameter e is unused. Consider adding logging to record the exception.

Suggested change

	public ResponseEntity<HotelController.ErrorResponse> handleOptimisticLockException(Exception e) {
	String message = "The room was just booked by someone else. Please refresh and try again.";
	return ResponseEntity.status(HttpStatus.CONFLICT)
	.body(new HotelController.ErrorResponse(message));
	}
	public ResponseEntity<HotelController.ErrorResponse> handleOptimisticLockException(Exception e) {
	// TODO: Add logging for the exception `e` for debugging purposes, e.g., using log.warn(...)
	String message = "The room was just booked by someone else. Please refresh and try again.";
	return ResponseEntity.status(HttpStatus.CONFLICT)
	.body(new HotelController.ErrorResponse(message));
	}

[gemini-code-assist]

The catch block is too broad. Catching RuntimeException can lead to false positives in this test, as any unexpected runtime error during booking would be counted as an optimistic locking failure. To make the test more precise and reliable, you should only catch the specific optimistic locking exceptions. If any other RuntimeException occurs, the test should fail to indicate an unexpected problem.

Suggested change

	} catch (RuntimeException | ObjectOptimisticLockingFailureException e) {
	} catch (ObjectOptimisticLockingFailureException e) {