Filter non-existing static resource locations

Same as a2c52a9, on the WebFlux side.

See gh-27538

spring-webflux/src/main/java/org/springframework/web/reactive/resource/ResourceWebHandler.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2020 the original author or authors.
+ * Copyright 2002-2021 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.
@@ -96,7 +96,9 @@ public class ResourceWebHandler implements WebHandler, InitializingBean {
 
 	private final List<String> locationValues = new ArrayList<>(4);
 
-	private final List<Resource> locations = new ArrayList<>(4);
+	private final List<Resource> locationResources = new ArrayList<>(4);
+
+	private final List<Resource> locationsToUse = new ArrayList<>(4);
 
 	private final List<ResourceResolver> resourceResolvers = new ArrayList<>(4);
 
@@ -147,9 +149,9 @@ public List<String> getLocationValues() {
 	 * for serving static resources.
 	 */
 	public void setLocations(@Nullable List<Resource> locations) {
-		this.locations.clear();
+		this.locationResources.clear();
 		if (locations != null) {
-			this.locations.addAll(locations);
+			this.locationResources.addAll(locations);
 		}
 	}
 
@@ -159,11 +161,18 @@ public void setLocations(@Nullable List<Resource> locations) {
 	 * <p>Note that if {@link #setLocationValues(List) locationValues} are provided,
 	 * instead of loaded Resource-based locations, this method will return
 	 * empty until after initialization via {@link #afterPropertiesSet()}.
+	 * <p><strong>Note:</strong> As of 5.3.11 the list of locations is filtered
+	 * to exclude those that don't actually exist and therefore the list returned
+	 * from this method may be a subset of all given locations.
 	 * @see #setLocationValues
 	 * @see #setLocations
 	 */
 	public List<Resource> getLocations() {
-		return this.locations;
+		if (this.locationsToUse.isEmpty()) {
+			// Possibly not yet initialized, return only what we have so far
+			return this.locationResources;
+		}
+		return this.locationsToUse;
 	}
 
 	/**
@@ -295,7 +304,7 @@ public void setUseLastModified(boolean useLastModified) {
 	public void afterPropertiesSet() throws Exception {
 		resolveResourceLocations();
 
-		if (logger.isWarnEnabled() && CollectionUtils.isEmpty(this.locations)) {
+		if (logger.isWarnEnabled() && CollectionUtils.isEmpty(getLocations())) {
 			logger.warn("Locations list is empty. No resources will be served unless a " +
 					"custom ResourceResolver is configured as an alternative to PathResourceResolver.");
 		}
@@ -316,21 +325,22 @@ public void afterPropertiesSet() throws Exception {
 	}
 
 	private void resolveResourceLocations() {
-		if (CollectionUtils.isEmpty(this.locationValues)) {
-			return;
-		}
-		else if (!CollectionUtils.isEmpty(this.locations)) {
-			throw new IllegalArgumentException("Please set either Resource-based \"locations\" or " +
-					"String-based \"locationValues\", but not both.");
+		List<Resource> result = new ArrayList<>(this.locationResources);
+
+		if (!this.locationValues.isEmpty()) {
+			Assert.notNull(this.resourceLoader,
+					"ResourceLoader is required when \"locationValues\" are configured.");
+			Assert.isTrue(CollectionUtils.isEmpty(this.locationResources), "Please set " +
+					"either Resource-based \"locations\" or String-based \"locationValues\", but not both.");
+			for (String location : this.locationValues) {
+				result.add(this.resourceLoader.getResource(location));
+			}
 		}
 
-		Assert.notNull(this.resourceLoader,
-				"ResourceLoader is required when \"locationValues\" are configured.");
+		result = result.stream().filter(Resource::exists).collect(Collectors.toList());
 
-		for (String location : this.locationValues) {
-			Resource resource = this.resourceLoader.getResource(location);
-			this.locations.add(resource);
-		}
+		this.locationsToUse.clear();
+		this.locationsToUse.addAll(result);
 	}
 
 	/**
@@ -339,7 +349,7 @@ else if (!CollectionUtils.isEmpty(this.locations)) {
 	 * match the {@link #setLocations locations} configured on this class.
 	 */
 	protected void initAllowedLocations() {
-		if (CollectionUtils.isEmpty(this.locations)) {
+		if (CollectionUtils.isEmpty(getLocations())) {
 			if (logger.isInfoEnabled()) {
 				logger.info("Locations list is empty. No resources will be served unless a " +
 						"custom ResourceResolver is configured as an alternative to PathResourceResolver.");
@@ -618,8 +628,8 @@ private Object formatLocations() {
 		if (!this.locationValues.isEmpty()) {
 			return this.locationValues.stream().collect(Collectors.joining("\", \"", "[\"", "\"]"));
 		}
-		else if (!this.locations.isEmpty()) {
-			return "[" + this.locations.toString()
+		if (!getLocations().isEmpty()) {
+			return "[" + getLocations().toString()
 					.replaceAll("class path resource", "Classpath")
 					.replaceAll("ServletContext resource", "ServletContext") + "]";
 		}

spring-webflux/src/test/java/org/springframework/web/reactive/resource/ResourceWebHandlerTests.java

@@ -253,6 +253,23 @@ public void getResourceFromFileSystem() throws Exception {
 		assertResponseBody(exchange, "h1 { color:red; }");
 	}
 
+	@Test  // gh-27538
+	public void filterNonExistingLocations() throws Exception {
+		List<Resource> inputLocations = Arrays.asList(
+				new ClassPathResource("test/", getClass()),
+				new ClassPathResource("testalternatepath/", getClass()),
+				new ClassPathResource("nosuchpath/", getClass()));
+
+		ResourceWebHandler handler = new ResourceWebHandler();
+		handler.setLocations(inputLocations);
+		handler.afterPropertiesSet();
+
+		List<Resource> actual = handler.getLocations();
+		assertThat(actual).hasSize(2);
+		assertThat(actual.get(0).getURL().toString()).endsWith("test/");
+		assertThat(actual.get(1).getURL().toString()).endsWith("testalternatepath/");
+	}
+
 	@Test // SPR-14577
 	public void getMediaTypeWithFavorPathExtensionOff() throws Exception {
 		List<Resource> paths = Collections.singletonList(new ClassPathResource("test/", getClass()));

spring-webmvc/src/main/java/org/springframework/web/servlet/resource/ResourceHttpRequestHandler.java

@@ -189,6 +189,9 @@ public void setLocations(List<Resource> locations) {
 	 * locations provided via {@link #setLocations(List) setLocations}.
 	 * <p>Note that the returned list is fully initialized only after
 	 * initialization via {@link #afterPropertiesSet()}.
+	 * <p><strong>Note:</strong> As of 5.3.11 the list of locations is filtered
+	 * to exclude those that don't actually exist and therefore the list returned
+	 * from this method may be a subset of all given locations.
 	 * @see #setLocationValues
 	 * @see #setLocations
 	 */
@@ -467,6 +470,7 @@ private void resolveResourceLocations() {
 		result.addAll(this.locationResources);
 		result = result.stream().filter(Resource::exists).collect(Collectors.toList());
 
+		this.locationsToUse.clear();
 		this.locationsToUse.addAll(result);
 	}