public static ExchangeFilterFunction errorHandler() {

    return ExchangeFilterFunction.ofResponseProcessor(clientResponse -> {

        if (clientResponse.statusCode().is5xxServerError()) {

            return clientResponse.bodyToMono(String.class)

                    .flatMap(errorBody -> Mono.error(new UserDefinedException1(errorBody)));

        } else if (clientResponse.statusCode().is4xxClientError()) {

            return clientResponse.bodyToMono(String.class)

                    .flatMap(errorBody -> Mono.error(new UserDefinedException2(errorBody)));

        } else {

            return Mono.just(clientResponse);

        }

    });

}

try {

UserDefinedResponse response = webClient

        .post()

        .body(Mono.just(userDefinedRequest), Map.class)

        .retrieve()

        .bodyToMono(UserDefinedResponse.class)

        .onErrorResume(Mono::error)

        .retryWhen(Retry.backoff(3, Duration.of(2, ChronoUnit.SECONDS))

                .onRetryExhaustedThrow((retryBackoffSpec, retrySignal) ->

new UserDefinedException(retrySignal.failure())))

        .block();

} catch(UserDefinedException userDefinedException){

//Error Handling logic

}