We will implement a new HandlerFilterFunction, SampleHandlerFilterFunction, in which we will look at a path variable (pathVariable) and check for its value. If the value is equal to value2, we will mark the status as BAD_REQUEST. It's important to note that since HandlerFilterFunction applies only to functional-based, even though the path variable value is equal to value2, the status is not stamped as BAD_REQUEST, and the response received is OK:

public class SampleHandlerFilterFunction implements 
        HandlerFilterFunction<ServerResponse, ServerResponse> {
    @Override
    public Mono<ServerResponse> filter(ServerRequest serverRequest, 
        HandlerFunction<ServerResponse> handlerFunction) {
        if (serverRequest.pathVariable("pathVariable")
                .equalsIgnoreCase("value2")) {
            return ServerResponse.status(BAD_REQUEST).build();
        }
        return handlerFunction.handle(serverRequest);
    }
}

SampleHandlerFilterFunction implements the HandlerFilterFunction class, and also implements the filter method. In this class, we will explicitly set the response status as a bad request, if a condition is met:

@Test
public void filtertest1_with_pathVariable_equalTo_value2_apply_HandlerFilterFunction() {
    webTestClient.get().uri("/filtertest1/value2")
        .exchange()
        .expectStatus().isOk();
}
@Test
public void filtertest2_with_pathVariable_equalTo_value2_apply_HandlerFilterFunction() {
    webTestClient.get().uri("/filtertest2/value2")
        .exchange()
        .expectStatus().isBadRequest();
}

In the preceding test cases, the path tested is different, and since HandlerFilterFunction applies only to functional-based, the response is OK when the path is filtertest1, and it's BAD_REQUEST when the path is filtertest2.