Remove concatMap in lookupRoute to improve throughput

Fixes gh-3291

Author: spencergibb

spring-cloud-gateway-server/src/main/java/org/springframework/cloud/gateway/handler/RoutePredicateHandlerMapping.java

@@ -128,21 +128,17 @@ private String getExchangeDesc(ServerWebExchange exchange) {
 	}
 
 	protected Mono<Route> lookupRoute(ServerWebExchange exchange) {
-		return this.routeLocator.getRoutes()
-			// individually filter routes so that filterWhen error delaying is not a
-			// problem
-			.concatMap(route -> Mono.just(route).filterWhen(r -> {
-				// add the current route we are testing
-				exchange.getAttributes().put(GATEWAY_PREDICATE_ROUTE_ATTR, r.getId());
-				return r.getPredicate().apply(exchange);
-			})
-				// instead of immediately stopping main flux due to error, log and
-				// swallow it
-				.doOnError(e -> logger.error("Error applying predicate for route: " + route.getId(), e))
-				.onErrorResume(e -> Mono.empty()))
-			// .defaultIfEmpty() put a static Route not found
-			// or .switchIfEmpty()
-			// .switchIfEmpty(Mono.<Route>empty().log("noroute"))
+		return this.routeLocator.getRoutes().filterWhen(route -> {
+			// add the current route we are testing
+			exchange.getAttributes().put(GATEWAY_PREDICATE_ROUTE_ATTR, route.getId());
+			try {
+				return route.getPredicate().apply(exchange);
+			}
+			catch (Exception e) {
+				logger.error("Error applying predicate for route: " + route.getId(), e);
+			}
+			return Mono.just(false);
+		})
 			.next()
 			// TODO: error handling
 			.map(route -> {

spring-cloud-gateway-server/src/test/java/org/springframework/cloud/gateway/handler/RoutePredicateHandlerMappingTests.java

@@ -71,7 +71,7 @@ public void lookupRouteFromAsyncPredicates(CapturedOutput capturedOutput) {
 		Route routeError = Route.async()
 			.id("routeError")
 			.uri("http://localhost")
-			.asyncPredicate(swe -> Mono.error(new IllegalStateException("boom1")))
+			.asyncPredicate(swe -> Mono.just(boom1()))
 			.build();
 		Route routeFail = Route.async().id("routeFail").uri("http://localhost").asyncPredicate(swe -> {
 			throw new IllegalStateException("boom2");
@@ -96,4 +96,8 @@ public void lookupRouteFromAsyncPredicates(CapturedOutput capturedOutput) {
 		Assertions.assertTrue(capturedOutput.getOut().contains("java.lang.IllegalStateException: boom2"));
 	}
 
+	boolean boom1() {
+		throw new IllegalStateException("boom1");
+	}
+
 }