Merge pull request #44535 from nosan

* pr/44535:
  Refactor ApplicationResourceLoader `preferFileResolution` support
  Improve ApplicationResourceLoader `preferFileResolution` support

Closes gh-44535

Author: philwebb

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/io/ApplicationResourceLoader.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2024 the original author or authors.
+ * Copyright 2012-2025 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.
@@ -16,9 +16,9 @@
 
 package org.springframework.boot.io;
 
+import java.util.Collections;
 import java.util.List;
 
-import org.springframework.core.io.ClassPathResource;
 import org.springframework.core.io.ContextResource;
 import org.springframework.core.io.DefaultResourceLoader;
 import org.springframework.core.io.FileSystemResource;
@@ -27,7 +27,6 @@
 import org.springframework.core.io.ResourceLoader;
 import org.springframework.core.io.support.SpringFactoriesLoader;
 import org.springframework.util.Assert;
-import org.springframework.util.ClassUtils;
 import org.springframework.util.StringUtils;
 
 /**
@@ -131,9 +130,8 @@ public static ResourceLoader get(ResourceLoader resourceLoader) {
 	 * {@code spring.factories}. The factories file will be resolved using the default
 	 * class loader at the time this call is made.
 	 * @param resourceLoader the delegate resource loader
-	 * @param preferFileResolution if file based resolution is preferred over
-	 * {@code ServletContextResource} or {@link ClassPathResource} when no resource prefix
-	 * is provided.
+	 * @param preferFileResolution if file based resolution is preferred when a suitable
+	 * {@link ResourceFilePathResolver} support the resource
 	 * @return a {@link ResourceLoader} instance
 	 * @since 3.4.1
 	 */
@@ -161,8 +159,10 @@ private static ResourceLoader get(ResourceLoader resourceLoader, SpringFactories
 			boolean preferFileResolution) {
 		Assert.notNull(resourceLoader, "'resourceLoader' must not be null");
 		Assert.notNull(springFactoriesLoader, "'springFactoriesLoader' must not be null");
-		return new ProtocolResolvingResourceLoader(resourceLoader, springFactoriesLoader.load(ProtocolResolver.class),
-				preferFileResolution);
+		List<ProtocolResolver> protocolResolvers = springFactoriesLoader.load(ProtocolResolver.class);
+		List<ResourceFilePathResolver> filePathResolvers = (preferFileResolution)
+				? springFactoriesLoader.load(ResourceFilePathResolver.class) : Collections.emptyList();
+		return new ProtocolResolvingResourceLoader(resourceLoader, protocolResolvers, filePathResolvers);
 	}
 
 	/**
@@ -210,30 +210,22 @@ public String getPathWithinContext() {
 	 */
 	private static class ProtocolResolvingResourceLoader implements ResourceLoader {
 
-		private static final String SERVLET_CONTEXT_RESOURCE_CLASS_NAME = "org.springframework.web.context.support.ServletContextResource";
-
 		private final ResourceLoader resourceLoader;
 
 		private final List<ProtocolResolver> protocolResolvers;
 
-		private final boolean preferFileResolution;
-
-		private Class<?> servletContextResourceClass;
+		private final List<ResourceFilePathResolver> filePathResolvers;
 
 		ProtocolResolvingResourceLoader(ResourceLoader resourceLoader, List<ProtocolResolver> protocolResolvers,
-				boolean preferFileResolution) {
+				List<ResourceFilePathResolver> filePathResolvers) {
 			this.resourceLoader = resourceLoader;
 			this.protocolResolvers = protocolResolvers;
-			this.preferFileResolution = preferFileResolution;
-			this.servletContextResourceClass = resolveServletContextResourceClass(
-					resourceLoader.getClass().getClassLoader());
+			this.filePathResolvers = filePathResolvers;
 		}
 
-		private static Class<?> resolveServletContextResourceClass(ClassLoader classLoader) {
-			if (!ClassUtils.isPresent(SERVLET_CONTEXT_RESOURCE_CLASS_NAME, classLoader)) {
-				return null;
-			}
-			return ClassUtils.resolveClassName(SERVLET_CONTEXT_RESOURCE_CLASS_NAME, classLoader);
+		@Override
+		public ClassLoader getClassLoader() {
+			return this.resourceLoader.getClassLoader();
 		}
 
 		@Override
@@ -247,24 +239,18 @@ public Resource getResource(String location) {
 				}
 			}
 			Resource resource = this.resourceLoader.getResource(location);
-			if (this.preferFileResolution
-					&& (isClassPathResourceByPath(location, resource) || isServletResource(resource))) {
-				resource = new ApplicationResource(location);
-			}
-			return resource;
+			String fileSystemPath = getFileSystemPath(location, resource);
+			return (fileSystemPath != null) ? new ApplicationResource(fileSystemPath) : resource;
 		}
 
-		private boolean isClassPathResourceByPath(String location, Resource resource) {
-			return (resource instanceof ClassPathResource) && !location.startsWith(CLASSPATH_URL_PREFIX);
-		}
-
-		private boolean isServletResource(Resource resource) {
-			return this.servletContextResourceClass != null && this.servletContextResourceClass.isInstance(resource);
-		}
-
-		@Override
-		public ClassLoader getClassLoader() {
-			return this.resourceLoader.getClassLoader();
+		private String getFileSystemPath(String location, Resource resource) {
+			for (ResourceFilePathResolver filePathResolver : this.filePathResolvers) {
+				String filePath = filePathResolver.resolveFilePath(location, resource);
+				if (filePath != null) {
+					return filePath;
+				}
+			}
+			return null;
 		}
 
 	}

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/io/ClassPathResourceFilePathResolver.java

@@ -0,0 +1,39 @@
+/*
+ * Copyright 2012-2025 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.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.io;
+
+import org.springframework.core.io.ClassPathResource;
+import org.springframework.core.io.Resource;
+import org.springframework.core.io.ResourceLoader;
+
+/**
+ * {@link ResourceFilePathResolver} for {@link ClassPathResource}.
+ *
+ * @author Phillip Webb
+ */
+class ClassPathResourceFilePathResolver implements ResourceFilePathResolver {
+
+	@Override
+	public String resolveFilePath(String location, Resource resource) {
+		return (resource instanceof ClassPathResource && !isClassPathUrl(location)) ? location : null;
+	}
+
+	private boolean isClassPathUrl(String location) {
+		return location.startsWith(ResourceLoader.CLASSPATH_URL_PREFIX);
+	}
+
+}

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/io/ResourceFilePathResolver.java

@@ -0,0 +1,42 @@
+/*
+ * Copyright 2012-2025 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.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.io;
+
+import org.springframework.core.io.FileSystemResource;
+import org.springframework.core.io.Resource;
+
+/**
+ * Strategy interface registered in {@code spring.factories} and used by
+ * {@link ApplicationResourceLoader} to determine the file path of loaded resource when it
+ * can also be represented as a {@link FileSystemResource}.
+ *
+ * @author Phillip Webb
+ * @since 3.4.5
+ */
+public interface ResourceFilePathResolver {
+
+	/**
+	 * Return the {@code path} of the given resource if it can also be represented as a
+	 * {@link FileSystemResource}.
+	 * @param location the location used to create the resource
+	 * @param resource the resource to check
+	 * @return the file path of the resource or {@code null} if the it is not possible to
+	 * represent the resource as a {@link FileSystemResource}.
+	 */
+	String resolveFilePath(String location, Resource resource);
+
+}

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/web/context/ServletContextResourceFilePathResolver.java

@@ -0,0 +1,46 @@
+/*
+ * Copyright 2012-2025 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.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.web.context;
+
+import org.springframework.boot.io.ResourceFilePathResolver;
+import org.springframework.core.io.Resource;
+import org.springframework.util.ClassUtils;
+import org.springframework.web.context.support.ServletContextResource;
+
+/**
+ * {@link ResourceFilePathResolver} for {@link ServletContextResource}.
+ *
+ * @author Phillip Webb
+ */
+class ServletContextResourceFilePathResolver implements ResourceFilePathResolver {
+
+	private static final String RESOURCE_CLASS_NAME = "org.springframework.web.context.support.ServletContextResource";
+
+	private final Class<?> resourceClass;
+
+	ServletContextResourceFilePathResolver() {
+		ClassLoader classLoader = getClass().getClassLoader();
+		this.resourceClass = ClassUtils.isPresent(RESOURCE_CLASS_NAME, classLoader)
+				? ClassUtils.resolveClassName(RESOURCE_CLASS_NAME, classLoader) : null;
+	}
+
+	@Override
+	public String resolveFilePath(String location, Resource resource) {
+		return (this.resourceClass != null && this.resourceClass.isInstance(resource)) ? location : null;
+	}
+
+}

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/web/reactive/context/FilteredReactiveWebContextResourceFilePathResolver.java

@@ -0,0 +1,34 @@
+/*
+ * Copyright 2012-2025 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.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.web.reactive.context;
+
+import org.springframework.boot.io.ResourceFilePathResolver;
+import org.springframework.core.io.Resource;
+
+/**
+ * {@link ResourceFilePathResolver} for {@link FilteredReactiveWebContextResource}.
+ *
+ * @author Dmytro Nosan
+ */
+class FilteredReactiveWebContextResourceFilePathResolver implements ResourceFilePathResolver {
+
+	@Override
+	public String resolveFilePath(String location, Resource resource) {
+		return (resource instanceof FilteredReactiveWebContextResource) ? location : null;
+	}
+
+}

spring-boot-project/spring-boot/src/main/resources/META-INF/spring.factories

@@ -105,3 +105,9 @@ org.springframework.boot.sql.init.dependency.AnnotationDependsOnDatabaseInitiali
 # Resource Locator Protocol Resolvers
 org.springframework.core.io.ProtocolResolver=\
 org.springframework.boot.io.Base64ProtocolResolver
+
+# Resource File Path Resolvers
+org.springframework.boot.io.ResourceFilePathResolver=\
+org.springframework.boot.io.ClassPathResourceFilePathResolver,\
+org.springframework.boot.web.context.ServletContextResourceFilePathResolver,\
+org.springframework.boot.web.reactive.context.FilteredReactiveWebContextResourceFilePathResolver

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/io/ApplicationResourceLoaderTests.java

@@ -24,7 +24,6 @@
 import java.util.Enumeration;
 import java.util.function.UnaryOperator;
 
-import jakarta.servlet.ServletContext;
 import org.junit.jupiter.api.Test;
 
 import org.springframework.boot.testsupport.classpath.resources.ResourcePath;
@@ -36,9 +35,6 @@
 import org.springframework.core.io.Resource;
 import org.springframework.core.io.ResourceLoader;
 import org.springframework.core.io.support.SpringFactoriesLoader;
-import org.springframework.mock.web.MockServletContext;
-import org.springframework.web.context.support.ServletContextResource;
-import org.springframework.web.context.support.ServletContextResourceLoader;
 
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatIllegalArgumentException;
@@ -196,19 +192,6 @@ void getResourceWithPreferFileResolutionWhenExplicitClassPathPrefix() {
 		assertThat(resource).isInstanceOf(ClassPathResource.class);
 	}
 
-	@Test
-	void getResourceWithPreferFileResolutionWhenPathWithServletContextResource() throws Exception {
-		ServletContext servletContext = new MockServletContext();
-		ServletContextResourceLoader servletContextResourceLoader = new ServletContextResourceLoader(servletContext);
-		ResourceLoader loader = ApplicationResourceLoader.get(servletContextResourceLoader, true);
-		Resource resource = loader.getResource("src/main/resources/a-file");
-		assertThat(resource).isInstanceOf(FileSystemResource.class);
-		assertThat(resource.getFile().getAbsoluteFile())
-			.isEqualTo(new File("src/main/resources/a-file").getAbsoluteFile());
-		ResourceLoader regularLoader = ApplicationResourceLoader.get(servletContextResourceLoader, false);
-		assertThat(regularLoader.getResource("src/main/resources/a-file")).isInstanceOf(ServletContextResource.class);
-	}
-
 	@Test
 	void getClassLoaderReturnsDelegateClassLoader() {
 		ClassLoader classLoader = new TestClassLoader(this::useTestProtocolResolversFactories);

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/web/context/ServletContextResourceFilePathResolverIntegrationTests.java

@@ -0,0 +1,54 @@
+/*
+ * Copyright 2012-2025 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.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.web.context;
+
+import java.io.File;
+
+import jakarta.servlet.ServletContext;
+import org.junit.jupiter.api.Test;
+
+import org.springframework.boot.io.ApplicationResourceLoader;
+import org.springframework.core.io.FileSystemResource;
+import org.springframework.core.io.Resource;
+import org.springframework.core.io.ResourceLoader;
+import org.springframework.mock.web.MockServletContext;
+import org.springframework.web.context.support.ServletContextResource;
+import org.springframework.web.context.support.ServletContextResourceLoader;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Integration tests for {@link ServletContextResourceFilePathResolver}.
+ *
+ * @author Phillip Webb
+ */
+class ServletContextResourceFilePathResolverIntegrationTests {
+
+	@Test
+	void getResourceWithPreferFileResolutionWhenPathWithServletContextResource() throws Exception {
+		ServletContext servletContext = new MockServletContext();
+		ServletContextResourceLoader servletContextResourceLoader = new ServletContextResourceLoader(servletContext);
+		ResourceLoader loader = ApplicationResourceLoader.get(servletContextResourceLoader, true);
+		Resource resource = loader.getResource("src/main/resources/a-file");
+		assertThat(resource).isInstanceOf(FileSystemResource.class);
+		assertThat(resource.getFile().getAbsoluteFile())
+			.isEqualTo(new File("src/main/resources/a-file").getAbsoluteFile());
+		ResourceLoader regularLoader = ApplicationResourceLoader.get(servletContextResourceLoader, false);
+		assertThat(regularLoader.getResource("src/main/resources/a-file")).isInstanceOf(ServletContextResource.class);
+	}
+
+}