ErrorResponseResolver.java

@Component
public class GlobalErrorWebExceptionHandler implements ErrorWebExceptionHandler {

  @Override
  public Mono<Void> handle(ServerWebExchange serverWebExchange, Throwable throwable) {
    ErrorAttribute errorAttribute = this.buildResponse(throwable);

    serverWebExchange.getResponse().setStatusCode(errorAttribute.getStatus());
    serverWebExchange.getResponse().getHeaders().setContentType(MediaType.APPLICATION_JSON);

    DataBufferFactory bufferFactory = serverWebExchange.getResponse().bufferFactory();
    DataBuffer dataBuffer = bufferFactory
        .wrap(errorAttribute.getErrorMessageBytes());
    return serverWebExchange.getResponse().writeWith(Mono.just(dataBuffer));
  }

  private ErrorAttribute buildResponse(Throwable throwable) {
    if (throwable instanceof GatewayException) {
      GatewayException ex = (GatewayException) throwable;
      ErrorCode errorCode = ex.getErrorCode();
      return new ErrorAttribute(errorCode.getHttpStatus(), JsonUtils
          .convertBytes(new Errors<>(errorCode.getCode(), ex.getMessage())));
    }

    ErrorCode errorCode = ErrorCode.SERVER_EXCEPTION;
    return new ErrorAttribute(errorCode.getHttpStatus(), JsonUtils
        .convertBytes(new Errors<>(errorCode.getCode(), throwable.getMessage())));
  }

  @AllArgsConstructor
  @Getter
  public static class ErrorAttribute {

    private final HttpStatus status;
    private final byte[] errorMessageBytes;

  }

}