Polish embedded tomcat setup

See gh-16446

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

@@ -55,7 +55,7 @@ class TomcatEmbeddedContext extends StandardContext {
 	@Override
 	public void setManager(Manager manager) {
 		if (manager instanceof ManagerBase) {
-			((ManagerBase) manager).setSessionIdGenerator(new LazySessionIdGenerator());
+			manager.setSessionIdGenerator(new LazySessionIdGenerator());
 		}
 		super.setManager(manager);
 	}

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

@@ -66,7 +66,7 @@ public class TomcatReactiveWebServerFactory extends AbstractReactiveWebServerFac
 
 	private File baseDirectory;
 
-	private List<Valve> engineValves = new ArrayList<>();
+	private final List<Valve> engineValves = new ArrayList<>();
 
 	private List<LifecycleListener> contextLifecycleListeners = getDefaultLifecycleListeners();
 

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

@@ -121,7 +121,7 @@ public class TomcatServletWebServerFactory extends AbstractServletWebServerFacto
 
 	private List<TomcatProtocolHandlerCustomizer<?>> tomcatProtocolHandlerCustomizers = new ArrayList<>();
 
-	private List<Connector> additionalTomcatConnectors = new ArrayList<>();
+	private final List<Connector> additionalTomcatConnectors = new ArrayList<>();
 
 	private ResourceLoader resourceLoader;
 
@@ -717,7 +717,7 @@ public class TomcatServletWebServerFactory extends AbstractServletWebServerFacto
 			if (event.getType().equals(Lifecycle.START_EVENT)) {
 				Context context = (Context) event.getLifecycle();
 				Manager manager = context.getManager();
-				if (manager != null && manager instanceof StandardManager) {
+				if (manager instanceof StandardManager) {
 					((StandardManager) manager).setPathname(null);
 				}
 			}