Unified Exception Handling in Spring Boot Using @ControllerAdvice, Custom Assertions, and Enums

In Java Spring development, excessive try‑catch blocks make code redundant and hard to read. The article proposes using try {...} catch {...} finally {...} sparingly and instead handling exceptions centrally.

Spring 3.2 introduced @ControllerAdvice and @ExceptionHandler , which can be applied to all controllers to define global exception handlers without coupling each controller to specific error‑handling code.

A custom Assert interface is created to replace manual null checks with Assert.notNull() , throwing business‑specific exceptions defined by enums that contain an error code and message.

Enums implementing BusinessExceptionAssert map each error scenario (e.g., BAD_LICENCE_TYPE , LICENCE_NOT_FOUND ) to a concrete BusinessException , eliminating the need for many separate exception classes.

The unified exception handler class annotated with @ControllerAdvice defines methods such as handleBusinessException , handleBaseException , handleServletException , handleBindException , and a generic handleException to process custom, servlet, validation, and unknown exceptions respectively, returning a consistent ErrorResponse containing code and message .

Special handling for production environments hides detailed error messages, returning generic messages like "Network error". Internationalization is supported by mapping error codes to localized messages.

Standard response structures ( BaseResponse , CommonResponse , QueryDataResponse ) and shortcut classes ( R , QR ) are introduced to unify API outputs.

Extensive code snippets illustrate the implementation of the Assert utilities, enums, exception handler, and service layer usage, demonstrating how to validate inputs, query data, and handle errors consistently across the application.