title: how can webflux handle global error, like 404 page not found
body: <p>i use @restcontrolleradvice and @ExceptionHandler , but i can handle controller exception. server error like 404, 500 can't handle.</p>
  
  <pre><code>@RestControllerAdvice
  public class HttpExceptionHandler {
  
      private static final Logger logger = LoggerFactory.getLogger(HttpExceptionHandler.class);
  
      @ExceptionHandler(value = Exception.class)
      public String exceptions(Exception e) {
          String code = Global.ERR_UNKNOWN;
          if (e instanceof MethodNotAllowedException) {
              code = Global.ERR_HTTP_METHOD;
          }
          return code;
      }
  }
  </code></pre>