Updates for optional hystrix deps

pom.xml

@@ -22,6 +22,7 @@
 		<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
 		<project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
 		<java.version>1.8</java.version>
+		<reactor.version>3.0.4.RELEASE</reactor.version>
 	</properties>
 
 	<dependencies>
@@ -69,10 +70,12 @@
 			<artifactId>spring-cloud-starter-hystrix</artifactId>
 			<optional>true</optional>
 		</dependency>
+		<!-- TODO: should be part of spring-cloud-starter-hystrix -->
 		<dependency>
 			<groupId>io.reactivex</groupId>
 			<artifactId>rxjava-reactive-streams</artifactId>
 			<version>1.2.1</version>
+			<optional>true</optional>
 		</dependency>
 		<dependency>
 			<groupId>org.springframework.boot</groupId>

src/main/java/org/springframework/cloud/gateway/config/GatewayAutoConfiguration.java

@@ -41,7 +41,10 @@ import org.springframework.cloud.gateway.handler.predicate.UrlRoutePredicate;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 
+import com.netflix.hystrix.HystrixObservableCommand;
+
 import reactor.ipc.netty.http.client.HttpClient;
+import rx.RxReactiveStreams;
 
 /**
  * @author Spencer Gibb
@@ -163,6 +166,7 @@ public class GatewayAutoConfiguration {
 	}
 
 	@Bean(name = "HystrixRouteFilter")
+	@ConditionalOnClass({HystrixObservableCommand.class, RxReactiveStreams.class})
 	public HystrixRouteFilter hystrixRouteFilter() {
 		return new HystrixRouteFilter();
 	}