improve performance of getHandlerInternal

[ShijunDeng]

In some scenarios, we need to get HandlerMethod ahead of org.springframework.web.reactive.DispatcherHandler, such as an implement of authentication by WebFilter

public class AuthFilter implements WebFilter, Ordered {

    @Autowired
    private RequestMappingHandlerMapping handlerMapping;

    @Override
    public Mono<Void> filter(ServerWebExchange exchange, WebFilterChain chain) {
        return handlerMapping.getHandler(exchange).switchIfEmpty(chain.filter(exchange))
            .flatMap(handler -> {
                    if (handler instanceof HandlerMethod) {
                        HandlerMethod methodHandle = (HandlerMethod) handler;
                        CheckPermission permission = methodHandle.getMethodAnnotation(CheckPermission.class);
                        if (Objects.isNull(permission)) {
                            permission = AnnotationUtils.findAnnotation(methodHandle.getBeanType(), CheckPermission.class);
                        }

                        if (Objects.nonNull(permission)) {
                            // TODO  do something..
                        }
                    }
                    return chain.filter(exchange);
                }
            );
    }
}

HandlerMethod is necessary but there is no alternative way to get it withon WebFilter, which limited the capabilities of WebFilter. so, we need call getHandler, however this may lead to repeated call of lookupHandlerMethod as issue:

spring-framework/spring-webflux/src/main/java/org/springframework/web/reactive/result/method/AbstractHandlerMethodMapping.java

Line 293 in 00da70e

public Mono<HandlerMethod> getHandlerInternal(ServerWebExchange exchange) {

To avoid duplicate search for HandlerMethod in mapping.getHandler , I suggest implementing a improved getHandlerInternal, in which HandlerMethod would be searched in attributes at first.

Object handlerMethod = exchange.getAttributes().get(BEST_MATCHING_HANDLER_ATTRIBUTE);
if (handlerMethod instanceof HandlerMethod) {
	return Mono.just((HandlerMethod) handlerMethod);
}

related issue：#29591

[rstoyanchev]

WebFilters are called first and are not meant to know what the DispatcherHandler will do or what controller method it will choose. You can of course call a HandlerMapping from a WebFilter, but that is not something that we recommend or support.