approach1

/*
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##################################################################################
######### IF YOU FOUND THIS GIST USEFUL, PLEASE LEAVE A STAR. THANKS. ############
##################################################################################
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*/


@ExceptionHandler(WebClientResponseException.class)
  public ResponseEntity handleWebClientException(WebClientResponseException ex){
  /*
  Here we can write complex conditional logic based on the response status, 
  by using methods like getStatusCode(), getRawStatusCode(), getStatusText(), getHeaders() 
  and getResponseBodyAsString(). 
  Also we can get reference of the request that was sent using the method getRequest.
  */
    return ResponseEntity.badRequest().body(ex.getResponseBodyAsString());
  }

approach2

@Bean
  public WebClient buildWebClient() {

    Function<ClientResponse, Mono<ClientResponse>> webclientResponseProcessor =
        clientResponse -> {
          HttpStatus responseStatus = clientResponse.statusCode();
          if (responseStatus.is4xxClientError()) {
            System.out.println("4xx error");
            return Mono.error(new MyCustomClientException());
          } else if (responseStatus.is5xxServerError()) {
            System.out.println("5xx error");
            return Mono.error(new MyCustomClientException());
          }
          return Mono.just(clientResponse);
        };

    return WebClient.builder()
        .filter(ExchangeFilterFunction.ofResponseProcessor(webclientResponseProcessor)).build();
  }

Spring WebClient Global Error Handling.md

Two approaches to handle error responses from Spring WebClient calls globally:

• Exceptions with webclients are all wrapped in WebClientResponseException class. So we can handle that using Spring's ExceptionHandler annotation.

• Using ExchangeFilterFunction while constructing the webclient bean.