Fall back to HTTP GET in case of 405 from HTTP HEAD

Closes gh-34217

spring-core/src/main/java/org/springframework/core/io/AbstractFileResolvingResource.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.
@@ -66,6 +66,20 @@ public abstract class AbstractFileResolvingResource extends AbstractResource {
 					else if (code == HttpURLConnection.HTTP_NOT_FOUND) {
 						return false;
 					}
+					else if (code == HttpURLConnection.HTTP_BAD_METHOD) {
+						con = url.openConnection();
+						customizeConnection(con);
+						if (con instanceof HttpURLConnection newHttpCon) {
+							code = newHttpCon.getResponseCode();
+							if (code == HttpURLConnection.HTTP_OK) {
+								return true;
+							}
+							else if (code == HttpURLConnection.HTTP_NOT_FOUND) {
+								return false;
+							}
+							httpCon = newHttpCon;
+						}
+					}
 				}
 				if (con.getContentLengthLong() > 0) {
 					return true;
@@ -111,6 +125,15 @@ public abstract class AbstractFileResolvingResource extends AbstractResource {
 				if (con instanceof HttpURLConnection httpCon) {
 					httpCon.setRequestMethod("HEAD");
 					int code = httpCon.getResponseCode();
+					if (code == HttpURLConnection.HTTP_BAD_METHOD) {
+						con = url.openConnection();
+						customizeConnection(con);
+						if (!(con instanceof HttpURLConnection newHttpCon)) {
+							return false;
+						}
+						code = newHttpCon.getResponseCode();
+						httpCon = newHttpCon;
+					}
 					if (code != HttpURLConnection.HTTP_OK) {
 						httpCon.disconnect();
 						return false;
@@ -259,7 +282,14 @@ public abstract class AbstractFileResolvingResource extends AbstractResource {
 			if (con instanceof HttpURLConnection httpCon) {
 				httpCon.setRequestMethod("HEAD");
 			}
-			return con.getContentLengthLong();
+			long length = con.getContentLengthLong();
+			if (length <= 0 && con instanceof HttpURLConnection httpCon &&
+					httpCon.getResponseCode() == HttpURLConnection.HTTP_BAD_METHOD) {
+				con = url.openConnection();
+				customizeConnection(con);
+				length = con.getContentLengthLong();
+			}
+			return length;
 		}
 	}
 
@@ -288,9 +318,17 @@ public abstract class AbstractFileResolvingResource extends AbstractResource {
 			httpCon.setRequestMethod("HEAD");
 		}
 		long lastModified = con.getLastModified();
-		if (fileCheck && lastModified == 0 && con.getContentLengthLong() <= 0) {
+		if (lastModified == 0) {
-			throw new FileNotFoundException(getDescription() +
+			if (con instanceof HttpURLConnection httpCon &&
-					" cannot be resolved in the file system for checking its last-modified timestamp");
+					httpCon.getResponseCode() == HttpURLConnection.HTTP_BAD_METHOD) {
+				con = url.openConnection();
+				customizeConnection(con);
+				lastModified = con.getLastModified();
+			}
+			if (fileCheck && con.getContentLengthLong() <= 0) {
+				throw new FileNotFoundException(getDescription() +
+						" cannot be resolved in the file system for checking its last-modified timestamp");
+			}
 		}
 		return lastModified;
 	}

spring-core/src/test/java/org/springframework/core/io/ResourceTests.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.
@@ -306,7 +306,9 @@ class ResourceTests {
 	@Nested
 	class UrlResourceTests {
 
-		private MockWebServer server = new MockWebServer();
+		private static final String LAST_MODIFIED = "Wed, 09 Apr 2014 09:57:42 GMT";
+
+		private final MockWebServer server = new MockWebServer();
 
 		@Test
 		void sameResourceWithRelativePathIsEqual() throws Exception {
@@ -385,22 +387,44 @@ class ResourceTests {
 
 		@Test
 		void missingRemoteResourceDoesNotExist() throws Exception {
-			String baseUrl = startServer();
+			String baseUrl = startServer(true);
 			UrlResource resource = new UrlResource(baseUrl + "/missing");
 			assertThat(resource.exists()).isFalse();
 		}
 
 		@Test
 		void remoteResourceExists() throws Exception {
-			String baseUrl = startServer();
+			String baseUrl = startServer(true);
 			UrlResource resource = new UrlResource(baseUrl + "/resource");
 			assertThat(resource.exists()).isTrue();
+			assertThat(resource.isReadable()).isTrue();
 			assertThat(resource.contentLength()).isEqualTo(6);
+			assertThat(resource.lastModified()).isGreaterThan(0);
+		}
+
+		@Test
+		void remoteResourceExistsFallback() throws Exception {
+			String baseUrl = startServer(false);
+			UrlResource resource = new UrlResource(baseUrl + "/resource");
+			assertThat(resource.exists()).isTrue();
+			assertThat(resource.isReadable()).isTrue();
+			assertThat(resource.contentLength()).isEqualTo(6);
+			assertThat(resource.lastModified()).isGreaterThan(0);
 		}
 
 		@Test
 		void canCustomizeHttpUrlConnectionForExists() throws Exception {
-			String baseUrl = startServer();
+			String baseUrl = startServer(true);
+			CustomResource resource = new CustomResource(baseUrl + "/resource");
+			assertThat(resource.exists()).isTrue();
+			RecordedRequest request = this.server.takeRequest();
+			assertThat(request.getMethod()).isEqualTo("HEAD");
+			assertThat(request.getHeader("Framework-Name")).isEqualTo("Spring");
+		}
+
+		@Test
+		void canCustomizeHttpUrlConnectionForExistsFallback() throws Exception {
+			String baseUrl = startServer(false);
 			CustomResource resource = new CustomResource(baseUrl + "/resource");
 			assertThat(resource.exists()).isTrue();
 			RecordedRequest request = this.server.takeRequest();
@@ -410,7 +434,7 @@ class ResourceTests {
 
 		@Test
 		void canCustomizeHttpUrlConnectionForRead() throws Exception {
-			String baseUrl = startServer();
+			String baseUrl = startServer(true);
 			CustomResource resource = new CustomResource(baseUrl + "/resource");
 			assertThat(resource.getInputStream()).hasContent("Spring");
 			RecordedRequest request = this.server.takeRequest();
@@ -420,7 +444,7 @@ class ResourceTests {
 
 		@Test
 		void useUserInfoToSetBasicAuth() throws Exception {
-			startServer();
+			startServer(true);
 			UrlResource resource = new UrlResource(
 					"http://alice:secret@localhost:" + this.server.getPort() + "/resource");
 			assertThat(resource.getInputStream()).hasContent("Spring");
@@ -436,8 +460,8 @@ class ResourceTests {
 			this.server.shutdown();
 		}
 
-		private String startServer() throws Exception {
+		private String startServer(boolean withHeadSupport) throws Exception {
-			this.server.setDispatcher(new ResourceDispatcher());
+			this.server.setDispatcher(new ResourceDispatcher(withHeadSupport));
 			this.server.start();
 			return "http://localhost:" + this.server.getPort();
 		}
@@ -456,15 +480,26 @@ class ResourceTests {
 
 		class ResourceDispatcher extends Dispatcher {
 
+			boolean withHeadSupport;
+
+			public ResourceDispatcher(boolean withHeadSupport) {
+				this.withHeadSupport = withHeadSupport;
+			}
+
 			@Override
 			public MockResponse dispatch(RecordedRequest request) {
 				if (request.getPath().equals("/resource")) {
 					return switch (request.getMethod()) {
-						case "HEAD" -> new MockResponse()
+						case "HEAD" -> (this.withHeadSupport ?
-									.addHeader("Content-Length", "6");
+								new MockResponse()
+										.addHeader("Content-Type", "text/plain")
+										.addHeader("Content-Length", "6")
+										.addHeader("Last-Modified", LAST_MODIFIED) :
+								new MockResponse().setResponseCode(405));
 						case "GET" -> new MockResponse()
-									.addHeader("Content-Length", "6")
 									.addHeader("Content-Type", "text/plain")
+									.addHeader("Content-Length", "6")
+									.addHeader("Last-Modified", LAST_MODIFIED)
 									.setBody("Spring");
 						default -> new MockResponse().setResponseCode(404);
 					};