CODE EXAMPLE FOR JAVA

exception handling

@RestController
@RequestMapping("/product")
@AllArgsConstructor
public class ProductController {
  public static final String TRACE = "trace";

  @Value("${reflectoring.trace:false}")
  private boolean printStackTrace;
  
  private final ProductService productService;

  @GetMapping("/{id}")
  public Product getProduct(@PathVariable String id){
    return productService.getProduct(id);
  }

  @PostMapping
  public Product addProduct(@RequestBody @Valid ProductInput input){
    return productService.addProduct(input);
  }

  @ExceptionHandler(NoSuchElementFoundException.class)
  @ResponseStatus(HttpStatus.NOT_FOUND)
  public ResponseEntity<ErrorResponse> handleItemNotFoundException(
      NoSuchElementFoundException exception, 
      WebRequest request
  ){
    log.error("Failed to find the requested element", exception);
    return buildErrorResponse(exception, HttpStatus.NOT_FOUND, request);
  }

  @ExceptionHandler(MethodArgumentNotValidException.class)
  @ResponseStatus(HttpStatus.UNPROCESSABLE_ENTITY)
  public ResponseEntity<ErrorResponse> handleMethodArgumentNotValid(
      MethodArgumentNotValidException ex,
      WebRequest request
  ) {
    ErrorResponse errorResponse = new ErrorResponse(
        HttpStatus.UNPROCESSABLE_ENTITY.value(), 
        "Validation error. Check 'errors' field for details."
    );
    
    for (FieldError fieldError : ex.getBindingResult().getFieldErrors()) {
      errorResponse.addValidationError(fieldError.getField(), 
          fieldError.getDefaultMessage());
    }
    return ResponseEntity.unprocessableEntity().body(errorResponse);
  }

  @ExceptionHandler(Exception.class)
  @ResponseStatus(HttpStatus.INTERNAL_SERVER_ERROR)
  public ResponseEntity<ErrorResponse> handleAllUncaughtException(
      Exception exception, 
      WebRequest request){
    log.error("Unknown error occurred", exception);
    return buildErrorResponse(
        exception,
        "Unknown error occurred", 
        HttpStatus.INTERNAL_SERVER_ERROR, 
        request
    );
  }

  private ResponseEntity<ErrorResponse> buildErrorResponse(
      Exception exception,
      HttpStatus httpStatus,
      WebRequest request
  ) {
    return buildErrorResponse(
        exception, 
        exception.getMessage(), 
        httpStatus, 
        request);
  }

  private ResponseEntity<ErrorResponse> buildErrorResponse(
      Exception exception,
      String message,
      HttpStatus httpStatus,
      WebRequest request
  ) {
    ErrorResponse errorResponse = new ErrorResponse(
        httpStatus.value(), 
        exception.getMessage()
    );
    
    if(printStackTrace && isTraceOn(request)){
      errorResponse.setStackTrace(ExceptionUtils.getStackTrace(exception));
    }
    return ResponseEntity.status(httpStatus).body(errorResponse);
  }

  private boolean isTraceOn(WebRequest request) {
    String [] value = request.getParameterValues(TRACE);
    return Objects.nonNull(value)
        && value.length > 0
        && value[0].contentEquals("true");
  }
}