You may register an error handler for a specific Throwable in the Routing.Builder method.

Routing routing = Routing.builder()
                        .error(MyException.class, (req, res, ex) -> { 
                            // handle the error, set the HTTP status code
                            res.send(errorDescriptionObject); 
                        })
                        .build

• Registers an error handler that handles MyException that are thrown from the upstream handlers
• Finishes the request handling by sending a response

Error handlers are called when

• an exception is thrown from a handler

• req.next(ex) is called, where ex is an instance of Throwable

As with the standard handlers, the error handler must either

• send a response

  .error(MyException.class, (req, res, ex) -> {
      res.status(Http.Status.BAD_REQUEST_400);
      res.send("Unable to parse request. Message: " + ex.getMessage());
  })

  content_copy Copied

• or, forward the error handling to the downstream error handlers

  .error(Throwable.class, (req, res, ex) -> {
      // some logic
      req.next(ex);
  })

  content_copy Copied

Error handling can’t be forwarded to the standard handlers. In fact, invoking req.next(ex) or req.next() in an error handler are equivalent.

.error(Throwable.class, (req, res, ex) -> {
    if (condition) {
        req.next(ex); 
    } else {
        req.next(); 
    }
})

• Call a downstream error handler with the Throwable instance.
• Here, req.next() is the same as req.next(ex). In both cases, the downstream error handler is called.

Default error handling