Use getTomcatWebServer to create TomcatWebServer instance

TomcatReactiveWebServerFactory's getTomcatWebServer is described as
being a hook point the can be overrideden to return a different
TomcatWebServer or to apply additional processing to the Tomcat
server. Previously, this did not work as the method was not called
to create the TomcatWebServer instance. Instead, TomcatWebServer was
instantiated and returned directly.

This commit updates TomcatReactiveWebServerFactory to call
getTomcatWebServer to create the TomcatWebServer instance. A test
has also been added to verify that the method is now used.

Fixes gh-20386

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/web/embedded/tomcat/TomcatReactiveWebServerFactory.java

 /*
- * Copyright 2012-2019 the original author or authors.
+ * Copyright 2012-2020 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -112,7 +112,7 @@ public class TomcatReactiveWebServerFactory extends AbstractReactiveWebServerFac
 		configureEngine(tomcat.getEngine());
 		TomcatHttpHandlerAdapter servlet = new TomcatHttpHandlerAdapter(httpHandler);
 		prepareContext(tomcat.getHost(), servlet);
-		return new TomcatWebServer(tomcat, getPort() >= 0);
+		return getTomcatWebServer(tomcat);
 	}
 
 	private void configureEngine(Engine engine) {

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/web/embedded/tomcat/TomcatReactiveWebServerFactoryTests.java

@@ -17,6 +17,7 @@
 package org.springframework.boot.web.embedded.tomcat;
 
 import java.util.Arrays;
+import java.util.concurrent.atomic.AtomicReference;
 
 import org.apache.catalina.Context;
 import org.apache.catalina.LifecycleEvent;
@@ -184,4 +185,19 @@ public class TomcatReactiveWebServerFactoryTests extends AbstractReactiveWebServ
 				.isInstanceOf(ConnectorStartFailedException.class);
 	}
 
+	@Test
+	public void whenGetTomcatWebServerIsOverriddenThenWebServerCreationCanBeCustomized() {
+		AtomicReference<TomcatWebServer> webServerReference = new AtomicReference<>();
+		TomcatWebServer webServer = (TomcatWebServer) new TomcatReactiveWebServerFactory() {
+
+			@Override
+			protected TomcatWebServer getTomcatWebServer(Tomcat tomcat) {
+				webServerReference.set(new TomcatWebServer(tomcat));
+				return webServerReference.get();
+			}
+
+		}.getWebServer(new EchoHandler());
+		assertThat(webServerReference).hasValue(webServer);
+	}
+
 }