Global Exception Handling

Introduction

A @ControllerAdvice class centralises exception-to-HTTP-response mapping across all controllers. No more try/catch in every endpoint — one place handles validation errors, not-found, auth failures and unexpected exceptions.

Informative example

Centralised error responses:

@RestControllerAdvice
public class GlobalExceptionHandler {

    @ExceptionHandler(ResourceNotFoundException.class)
    ResponseEntity<ErrorResponse> notFound(ResourceNotFoundException ex) {
        return ResponseEntity.status(404)
            .body(new ErrorResponse("NOT_FOUND", ex.getMessage()));
    }

    @ExceptionHandler(MethodArgumentNotValidException.class)
    ResponseEntity<ErrorResponse> validation(MethodArgumentNotValidException ex) {
        var errors = ex.getBindingResult().getFieldErrors().stream()
            .collect(toMap(FieldError::getField, FieldError::getDefaultMessage));
        return ResponseEntity.badRequest()
            .body(new ErrorResponse("VALIDATION_FAILED", errors));
    }

    @ExceptionHandler(Exception.class)
    ResponseEntity<ErrorResponse> fallback(Exception ex) {
        log.error("Unhandled", ex);
        return ResponseEntity.status(500)
            .body(new ErrorResponse("INTERNAL_ERROR", "Something went wrong"));
    }
}

Best practices

• Never expose stack traces to clients in production.
• Use consistent error response shape: code, message, details, timestamp.
• Log the full exception server-side; return safe message client-side.

Purpose of this lesson

Master Global Exception Handling so you can apply it confidently in production Java code, technical interviews, and code reviews.

Step-by-step explanation

1. Understand the core idea behind Global Exception Handling.
2. Walk through the runnable example and tweak it in the playground.
3. Apply the pattern in a small Spring Boot or CLI exercise of your own.
4. Re-read the common mistakes and interview Q&A to lock the concept in.

Interactive workflow diagram

Useful template

@ExceptionHandler(ResourceNotFoundException.class)
ProblemDetail notFound(ResourceNotFoundException ex) {
  return ProblemDetail.forStatusAndDetail(NOT_FOUND, ex.getMessage());
}

Debugging tips

• Read the full stack trace — Java's exception messages name the offending class and line.
• Reproduce in the smallest possible main() method before fixing in the real app.
• Use IntelliJ's debugger breakpoints and 'Evaluate Expression' rather than scattering System.out.

Optimization strategies

• Profile before optimizing — JFR (Java Flight Recorder) and async-profiler reveal real hotspots.
• Prefer immutable data and stream pipelines over hand-rolled loops when readability matters.
• Reach for the right JDK collection (ArrayList vs LinkedList vs ArrayDeque) before writing custom data structures.

Enterprise example

Teams at Netflix, Uber and Goldman Sachs apply Global Exception Handling daily — usually wrapped behind Spring Boot services with observability hooks (Micrometer + OpenTelemetry).

Interview questions & answers

Summary

In this lesson you learned Global Exception Handling — the concept, syntax, a runnable example, and the production pitfalls to avoid. Apply it in the playground before moving on.