Add Logging

Now if the ServletRegistration API available message is shown, it will
also be accompanied with a startup warning in the logs.

Closes gh-14221

config/src/main/java/org/springframework/security/config/annotation/web/AbstractRequestMatcherRegistry.java

@@ -30,6 +30,9 @@
 import javax.servlet.ServletRegistration;
 import javax.servlet.http.HttpServletRequest;
 
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+
 import org.springframework.beans.factory.NoSuchBeanDefinitionException;
 import org.springframework.context.ApplicationContext;
 import org.springframework.http.HttpMethod;
@@ -75,6 +78,8 @@ public abstract class AbstractRequestMatcherRegistry<C> {
 				AbstractRequestMatcherRegistry.class.getClassLoader());
 	}
 
+	private final Log logger = LogFactory.getLog(getClass());
+
 	protected final void setApplicationContext(ApplicationContext context) {
 		this.context = context;
 	}
@@ -326,6 +331,10 @@ public C requestMatchers(HttpMethod method, String... patterns) {
 				matchers.add(resolve(ant, mvc, servletContext));
 			}
 			else {
+				this.logger
+					.warn("The ServletRegistration API was not available at startup time. This may be due to a misconfiguration; "
+							+ "if you are using AbstractSecurityWebApplicationInitializer, please double-check the recommendations outlined in "
+							+ "https://docs.spring.io/spring-security/reference/servlet/configuration/java.html#abstractsecuritywebapplicationinitializer-with-spring-mvc");
 				matchers.add(new DeferredRequestMatcher((request) -> resolve(ant, mvc, request.getServletContext()),
 						mvc, ant));
 			}