Enrich error response for invalid filter/predicate requests in actuator

In the previous implementation, server responds 400 Bad Request when no existing predicate or filter matches with the specified in the request (See `GatewayControllerEndpointTests.testPostRouteWithNotExistingFilter` & `GatewayControllerEndpointTests.testPostRouteWithNotExistingPredicate`).

This change replaces the filter by an exception that can take the advantage of the default `ExceptionHandler` including a body with more details specified by the server. In order to get the message that helps the client to diagnose the problem, the property `server.error.include-message=always` is required to be configured.

Example:
`POST /actuator/gateway/routes/invalid-route-test` request

Response
```
HTTP 400 Bad Request
Payload

{
    "timestamp": "2021-07-27T08:55:35.596+00:00",
    "path": "/actuator/gateway/routes/invalid-route-test",
    "status": 400,
    "error": "Bad Request",
    "message": "Invalid FilterDefinition: [InvalidFilter]",
    "requestId": "e5551c86-6, L:/0:0:0:0:0:0:0:1:8080 - R:/0:0:0:0:0:0:0:1:50437"
}
```

Fixes gh-2107
Fixes gh-2311

spring-cloud-gateway-server/src/main/java/org/springframework/cloud/gateway/actuate/AbstractGatewayControllerEndpoint.java

@@ -19,6 +19,8 @@ package org.springframework.cloud.gateway.actuate;
 import java.net.URI;
 import java.util.HashMap;
 import java.util.List;
+import java.util.Set;
+import java.util.stream.Collectors;
 
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
@@ -26,8 +28,10 @@ import reactor.core.publisher.Flux;
 import reactor.core.publisher.Mono;
 
 import org.springframework.cloud.gateway.event.RefreshRoutesEvent;
+import org.springframework.cloud.gateway.filter.FilterDefinition;
 import org.springframework.cloud.gateway.filter.GlobalFilter;
 import org.springframework.cloud.gateway.filter.factory.GatewayFilterFactory;
+import org.springframework.cloud.gateway.handler.predicate.PredicateDefinition;
 import org.springframework.cloud.gateway.handler.predicate.RoutePredicateFactory;
 import org.springframework.cloud.gateway.route.RouteDefinition;
 import org.springframework.cloud.gateway.route.RouteDefinitionLocator;
@@ -37,12 +41,14 @@ import org.springframework.cloud.gateway.support.NotFoundException;
 import org.springframework.context.ApplicationEventPublisher;
 import org.springframework.context.ApplicationEventPublisherAware;
 import org.springframework.core.Ordered;
+import org.springframework.http.HttpStatus;
 import org.springframework.http.ResponseEntity;
 import org.springframework.web.bind.annotation.DeleteMapping;
 import org.springframework.web.bind.annotation.GetMapping;
 import org.springframework.web.bind.annotation.PathVariable;
 import org.springframework.web.bind.annotation.PostMapping;
 import org.springframework.web.bind.annotation.RequestBody;
+import org.springframework.web.server.ResponseStatusException;
 
 /**
  * @author Spencer Gibb
@@ -129,8 +135,9 @@ public class AbstractGatewayControllerEndpoint implements ApplicationEventPublis
 	@SuppressWarnings("unchecked")
 	public Mono<ResponseEntity<Object>> save(@PathVariable String id, @RequestBody RouteDefinition route) {
 
-		return Mono.just(route).filter(this::validateRouteDefinition)
-				.flatMap(routeDefinition -> this.routeDefinitionWriter.save(Mono.just(routeDefinition).map(r -> {
+		return Mono.just(route).doOnNext(this::validateRouteDefinition)
+				.flatMap(routeDefinition -> this.routeDefinitionWriter
+						.save(Mono.just(routeDefinition).map(r -> {
 					r.setId(id);
 					log.debug("Saving route: " + route);
 					return r;
@@ -138,17 +145,40 @@ public class AbstractGatewayControllerEndpoint implements ApplicationEventPublis
 				.switchIfEmpty(Mono.defer(() -> Mono.just(ResponseEntity.badRequest().build())));
 	}
 
-	private boolean validateRouteDefinition(RouteDefinition routeDefinition) {
-		boolean hasValidFilterDefinitions = routeDefinition.getFilters().stream()
-				.allMatch(filterDefinition -> GatewayFilters.stream().anyMatch(
-						gatewayFilterFactory -> filterDefinition.getName().equals(gatewayFilterFactory.name())));
+	private void validateRouteDefinition(RouteDefinition routeDefinition) {
+		Set<String> unavailableFilterDefinitions = routeDefinition.getFilters().stream()
+				.filter(rd -> !isAvailable(rd)).map(FilterDefinition::getName)
+				.collect(Collectors.toSet());
 
-		boolean hasValidPredicateDefinitions = routeDefinition.getPredicates().stream()
-				.allMatch(predicateDefinition -> routePredicates.stream()
-						.anyMatch(routePredicate -> predicateDefinition.getName().equals(routePredicate.name())));
-		log.debug("FilterDefinitions valid: " + hasValidFilterDefinitions);
-		log.debug("PredicateDefinitions valid: " + hasValidPredicateDefinitions);
-		return hasValidFilterDefinitions && hasValidPredicateDefinitions;
+		Set<String> unavailablePredicatesDefinitions = routeDefinition.getPredicates()
+				.stream().filter(rd -> !isAvailable(rd)).map(PredicateDefinition::getName)
+				.collect(Collectors.toSet());
+		if (!unavailableFilterDefinitions.isEmpty()) {
+			handleUnavailableDefinition(FilterDefinition.class.getSimpleName(),
+					unavailableFilterDefinitions);
+		}
+		else if (!unavailablePredicatesDefinitions.isEmpty()) {
+			handleUnavailableDefinition(PredicateDefinition.class.getSimpleName(),
+					unavailablePredicatesDefinitions);
+		}
+	}
+
+	private void handleUnavailableDefinition(String simpleName,
+			Set<String> unavailableDefinitions) {
+		final String errorMessage = String.format("Invalid %s: %s", simpleName,
+				unavailableDefinitions);
+		log.debug(errorMessage);
+		throw new ResponseStatusException(HttpStatus.BAD_REQUEST, errorMessage);
+	}
+
+	private boolean isAvailable(FilterDefinition filterDefinition) {
+		return GatewayFilters.stream().anyMatch(gatewayFilterFactory -> filterDefinition
+				.getName().equals(gatewayFilterFactory.name()));
+	}
+
+	private boolean isAvailable(PredicateDefinition predicateDefinition) {
+		return routePredicates.stream().anyMatch(routePredicate -> predicateDefinition
+				.getName().equals(routePredicate.name()));
 	}
 
 	@DeleteMapping("/routes/{id}")

spring-cloud-gateway-server/src/test/java/org/springframework/cloud/gateway/actuate/GatewayControllerEndpointTests.java

@@ -151,7 +151,8 @@ public class GatewayControllerEndpointTests {
 
 		testClient.post().uri("http://localhost:" + port + "/actuator/gateway/routes/test-route")
 				.accept(MediaType.APPLICATION_JSON).body(BodyInserters.fromValue(testRouteDefinition)).exchange()
-				.expectStatus().isBadRequest();
+				.expectStatus().isBadRequest().expectBody().jsonPath("$.message")
+				.isEqualTo("Invalid FilterDefinition: [NotExistingFilter]");
 	}
 
 	@Test
@@ -165,7 +166,8 @@ public class GatewayControllerEndpointTests {
 
 		testClient.post().uri("http://localhost:" + port + "/actuator/gateway/routes/test-route")
 				.accept(MediaType.APPLICATION_JSON).body(BodyInserters.fromValue(testRouteDefinition)).exchange()
-				.expectStatus().isBadRequest();
+				.expectStatus().isBadRequest().expectBody().jsonPath("$.message")
+				.isEqualTo("Invalid PredicateDefinition: [NotExistingPredicate]");
 	}
 
 	@SpringBootConfiguration