Simplify UrlFileNameViewController#getViewNameForUrlPath()

Closes gh-24419

spring-webmvc/src/main/java/org/springframework/web/servlet/mvc/UrlFilenameViewController.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2020 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.
@@ -125,13 +125,7 @@ public class UrlFilenameViewController extends AbstractUrlViewController {
 	 * @see #postProcessViewName
 	 */
 	protected String getViewNameForUrlPath(String uri) {
-		String viewName = this.viewNameCache.get(uri);
-		if (viewName == null) {
-			viewName = extractViewNameFromUrlPath(uri);
-			viewName = postProcessViewName(viewName);
-			this.viewNameCache.put(uri, viewName);
-		}
-		return viewName;
+		return this.viewNameCache.computeIfAbsent(uri, u -> postProcessViewName(extractViewNameFromUrlPath(u)));
 	}
 
 	/**