Allow RoutePredicateHandlerMapping customization

Allow bean overriding and add a property to set the order.

spring.cloud.gateway.handler-mapping.order=1

Fixes gh-2469

Author: spencergibb

spring-cloud-gateway-server/src/main/java/org/springframework/cloud/gateway/config/GatewayAutoConfiguration.java

@@ -251,6 +251,7 @@ public GlobalCorsProperties globalCorsProperties() {
 	}
 
 	@Bean
+	@ConditionalOnMissingBean
 	public RoutePredicateHandlerMapping routePredicateHandlerMapping(FilteringWebHandler webHandler,
 			RouteLocator routeLocator, GlobalCorsProperties globalCorsProperties, Environment environment) {
 		return new RoutePredicateHandlerMapping(webHandler, routeLocator, globalCorsProperties, environment);

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

@@ -20,6 +20,7 @@
 
 import reactor.core.publisher.Mono;
 
+import org.springframework.cloud.gateway.config.GatewayProperties;
 import org.springframework.cloud.gateway.config.GlobalCorsProperties;
 import org.springframework.cloud.gateway.route.Route;
 import org.springframework.cloud.gateway.route.RouteLocator;
@@ -55,7 +56,7 @@ public RoutePredicateHandlerMapping(FilteringWebHandler webHandler, RouteLocator
 
 		this.managementPort = getPortProperty(environment, "management.server.");
 		this.managementPortType = getManagementPortType(environment);
-		setOrder(1);
+		setOrder(environment.getProperty(GatewayProperties.PREFIX + ".handler-mapping.order", Integer.class, 1));
 		setCorsConfigurations(globalCorsProperties.getCorsConfigurations());
 	}
 

spring-cloud-gateway-server/src/main/resources/META-INF/additional-spring-configuration-metadata.json

@@ -359,6 +359,12 @@
       "type": "java.lang.Boolean",
       "description": "If global CORS config should be added to the URL handler.",
       "defaultValue": "false"
+    },
+    {
+      "name": "spring.cloud.gateway.handler-mapping.order",
+      "type": "java.lang.Integer",
+      "description": "The order of RoutePredicateHandlerMapping.",
+      "defaultValue": "1"
     }
   ]
 }