Add explicit FileSystemResource path check for trailing slash

Closes gh-34509

Author: jhoeller

Diff for: spring-webflux/src/main/java/org/springframework/web/reactive/resource/ResourceHandlerUtils.java

@@ -24,7 +24,7 @@
 import org.apache.commons.logging.LogFactory;
 
 import org.springframework.core.io.ClassPathResource;
-import org.springframework.core.io.PathResource;
+import org.springframework.core.io.FileSystemResource;
 import org.springframework.core.io.Resource;
 import org.springframework.core.io.UrlResource;
 import org.springframework.core.log.LogFormatUtils;
@@ -57,15 +57,18 @@ public static void assertResourceLocation(@Nullable Resource location) {
 		Assert.notNull(location, "Resource location must not be null");
 		try {
 			String path;
-			if (location instanceof PathResource) {
+			if (location instanceof org.springframework.core.io.PathResource) {
 				return;
 			}
-			else if (location instanceof UrlResource) {
-				path = location.getURL().toExternalForm();
+			else if (location instanceof FileSystemResource fileSystemResource) {
+				path = fileSystemResource.getPath();
 			}
 			else if (location instanceof ClassPathResource classPathResource) {
 				path = classPathResource.getPath();
 			}
+			else if (location instanceof UrlResource) {
+				path = location.getURL().toExternalForm();
+			}
 			else {
 				path = location.getURL().getPath();
 			}

Diff for: spring-webflux/src/test/java/org/springframework/web/reactive/function/server/PathResourceLookupFunctionTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2024 the original author or authors.
+ * Copyright 2002-2025 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.
@@ -26,6 +26,7 @@
 import reactor.test.StepVerifier;
 
 import org.springframework.core.io.ClassPathResource;
+import org.springframework.core.io.FileSystemResource;
 import org.springframework.core.io.Resource;
 import org.springframework.web.testfixture.http.server.reactive.MockServerHttpRequest;
 import org.springframework.web.testfixture.server.MockServerWebExchange;
@@ -39,8 +40,7 @@ class PathResourceLookupFunctionTests {
 	void normal() throws Exception {
 		ClassPathResource location = new ClassPathResource("org/springframework/web/reactive/function/server/");
 
-		PathResourceLookupFunction
-				function = new PathResourceLookupFunction("/resources/**", location);
+		PathResourceLookupFunction function = new PathResourceLookupFunction("/resources/**", location);
 		MockServerHttpRequest mockRequest = MockServerHttpRequest.get("https://localhost/resources/response.txt").build();
 		ServerRequest request = new DefaultServerRequest(MockServerWebExchange.from(mockRequest), Collections.emptyList());
 		Mono<Resource> result = function.apply(request);
@@ -124,4 +124,17 @@ void composeResourceLookupFunction() {
 				.verify();
 	}
 
+	@Test
+	@SuppressWarnings("removal")
+	void withPathResource() {
+		org.springframework.core.io.PathResource location = new org.springframework.core.io.PathResource("/static/");
+		PathResourceLookupFunction function = new PathResourceLookupFunction("/resources/**", location);
+	}
+
+	@Test
+	void withFileSystemResource() {
+		FileSystemResource location = new FileSystemResource("/static/");
+		PathResourceLookupFunction function = new PathResourceLookupFunction("/resources/**", location);
+	}
+
 }

Diff for: spring-webmvc/src/main/java/org/springframework/web/servlet/resource/ResourceHandlerUtils.java

@@ -24,7 +24,7 @@
 import org.apache.commons.logging.LogFactory;
 
 import org.springframework.core.io.ClassPathResource;
-import org.springframework.core.io.PathResource;
+import org.springframework.core.io.FileSystemResource;
 import org.springframework.core.io.Resource;
 import org.springframework.core.io.UrlResource;
 import org.springframework.core.log.LogFormatUtils;
@@ -58,15 +58,18 @@ public static void assertResourceLocation(@Nullable Resource location) {
 		Assert.notNull(location, "Resource location must not be null");
 		try {
 			String path;
-			if (location instanceof PathResource) {
+			if (location instanceof org.springframework.core.io.PathResource) {
 				return;
 			}
-			else if (location instanceof UrlResource) {
-				path = location.getURL().toExternalForm();
+			else if (location instanceof FileSystemResource fileSystemResource) {
+				path = fileSystemResource.getPath();
 			}
 			else if (location instanceof ClassPathResource classPathResource) {
 				path = classPathResource.getPath();
 			}
+			else if (location instanceof UrlResource) {
+				path = location.getURL().toExternalForm();
+			}
 			else {
 				path = location.getURL().getPath();
 			}

Diff for: spring-webmvc/src/test/java/org/springframework/web/servlet/function/PathResourceLookupFunctionTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2023 the original author or authors.
+ * Copyright 2002-2025 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.
@@ -24,6 +24,7 @@
 import org.junit.jupiter.api.Test;
 
 import org.springframework.core.io.ClassPathResource;
+import org.springframework.core.io.FileSystemResource;
 import org.springframework.core.io.Resource;
 import org.springframework.web.servlet.handler.PathPatternsTestUtils;
 
@@ -102,4 +103,17 @@ private ServerRequest initRequest(String httpMethod, String requestUri) {
 				Collections.emptyList());
 	}
 
+	@Test
+	@SuppressWarnings("removal")
+	void withPathResource() {
+		org.springframework.core.io.PathResource location = new org.springframework.core.io.PathResource("/static/");
+		PathResourceLookupFunction function = new PathResourceLookupFunction("/resources/**", location);
+	}
+
+	@Test
+	void withFileSystemResource() {
+		FileSystemResource location = new FileSystemResource("/static/");
+		PathResourceLookupFunction function = new PathResourceLookupFunction("/resources/**", location);
+	}
+
 }