Improve Error Message When Registration Missing

Closes gh-15363

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

@@ -434,7 +434,7 @@ private boolean isDispatcherServlet(ServletRegistration registration) {
 		}
 	}
 
-	private String computeErrorMessage(Collection<? extends ServletRegistration> registrations) {
+	private static String computeErrorMessage(Collection<? extends ServletRegistration> registrations) {
 		String template = "This method cannot decide whether these patterns are Spring MVC patterns or not. "
 				+ "If this endpoint is a Spring MVC endpoint, please use requestMatchers(MvcRequestMatcher); "
 				+ "otherwise, please use requestMatchers(AntPathRequestMatcher).\n\n"
@@ -628,7 +628,7 @@ static class DispatcherServletRequestMatcher implements RequestMatcher {
 		public boolean matches(HttpServletRequest request) {
 			String name = request.getHttpServletMapping().getServletName();
 			ServletRegistration registration = this.servletContext.getServletRegistration(name);
-			Assert.notNull(name, "Failed to find servlet [" + name + "] in the servlet context");
+			Assert.notNull(registration, computeErrorMessage(this.servletContext.getServletRegistrations().values()));
 			try {
 				Class<?> clazz = Class.forName(registration.getClassName());
 				return DispatcherServlet.class.isAssignableFrom(clazz);
@@ -670,18 +670,12 @@ RequestMatcher requestMatcher(HttpServletRequest request) {
 
 		@Override
 		public boolean matches(HttpServletRequest request) {
-			if (this.dispatcherServlet.matches(request)) {
-				return this.mvc.matches(request);
-			}
-			return this.ant.matches(request);
+			return requestMatcher(request).matches(request);
 		}
 
 		@Override
 		public MatchResult matcher(HttpServletRequest request) {
-			if (this.dispatcherServlet.matches(request)) {
-				return this.mvc.matcher(request);
-			}
-			return this.ant.matcher(request);
+			return requestMatcher(request).matcher(request);
 		}
 
 		@Override

config/src/test/java/org/springframework/security/config/annotation/web/AbstractRequestMatcherRegistryTests.java

@@ -400,6 +400,19 @@ public HttpServletMapping getHttpServletMapping() {
 		verifyNoMoreInteractions(mvc);
 	}
 
+	@Test
+	public void matchesWhenNoMappingThenException() {
+		MockServletContext servletContext = new MockServletContext();
+		servletContext.addServlet("default", DispatcherServlet.class).addMapping("/");
+		servletContext.addServlet("path", Servlet.class).addMapping("/services/*");
+		MvcRequestMatcher mvc = mock(MvcRequestMatcher.class);
+		AntPathRequestMatcher ant = mock(AntPathRequestMatcher.class);
+		DispatcherServletDelegatingRequestMatcher requestMatcher = new DispatcherServletDelegatingRequestMatcher(ant,
+				mvc, servletContext);
+		MockHttpServletRequest request = new MockHttpServletRequest("GET", "/services/endpoint");
+		assertThatExceptionOfType(IllegalArgumentException.class).isThrownBy(() -> requestMatcher.matcher(request));
+	}
+
 	private void mockMvcIntrospector(boolean isPresent) {
 		ApplicationContext context = this.matcherRegistry.getApplicationContext();
 		given(context.containsBean("mvcHandlerMappingIntrospector")).willReturn(isPresent);