WebExceptionHandler : How to write a body with Spring Webflux

Question

I want to handle the Exception of my api by adding a WebExceptionHandler. I can change the status code, but I am stuck when i want to change the body of the response : ex adding the exception message or a custom object.

Does anyone have exemple ?

How I add my WebExceptionHandler :

HttpHandler httpHandler = WebHttpHandlerBuilder.webHandler(toHttpHandler(routerFunction))
  .prependExceptionHandler((serverWebExchange, exception) -> {

      exchange.getResponse().setStatusCode(myStatusGivenTheException);
      exchange.getResponse().writeAndFlushWith(??)
      return Mono.empty();

  }).build();

Answer 1

WebExceptionHandler is rather low level, so you have to directly deal with the request/response exchange.

Note that:

• the Mono<Void> return type should signal the end of the response handling; this is why it should be connected to the Publisher writing the response
• at this level, you're dealing directly with data buffers (no serialization support available)

Your WebExceptionHandler could look like this:

(serverWebExchange, exception) -> {

  exchange.getResponse().setStatusCode(myStatusGivenTheException);
  byte[] bytes = "Some text".getBytes(StandardCharsets.UTF_8);
  DataBuffer buffer = exchange.getResponse().bufferFactory().wrap(bytes);
  return exchange.getResponse().writeWith(Flux.just(buffer));
}