Return URL-decoded file name from UrlResource#getFilename()

Prior to this commit, UrlResource#getFilename() returned the filename
of the resource URL-encoded which is in contrast to what
FileSystemResource#getFilename() returns for an equivalent resource.

In addition, users most likely expect that a filename returned from a
method defined in the Resource interface is unencoded.

This commit therefore revises UrlResource#getFilename() so that it
always returns the filename URL-decoded.

Closes gh-29261

spring-core/src/main/java/org/springframework/core/io/Resource.java

@@ -158,10 +158,11 @@ default ReadableByteChannel readableChannel() throws IOException {
 	Resource createRelative(String relativePath) throws IOException;
 
 	/**
-	 * Determine a filename for this resource, i.e. typically the last
-	 * part of the path: for example, "myfile.txt".
+	 * Determine the filename for this resource — typically the last
+	 * part of the path — for example, {@code "myfile.txt"}.
 	 * <p>Returns {@code null} if this type of resource does not
 	 * have a filename.
+	 * <p>Implementations are encouraged to return the filename unencoded.
 	 */
 	@Nullable
 	String getFilename();

spring-core/src/main/java/org/springframework/core/io/UrlResource.java

@@ -26,6 +26,8 @@
 import java.net.URISyntaxException;
 import java.net.URL;
 import java.net.URLConnection;
+import java.net.URLDecoder;
+import java.nio.charset.StandardCharsets;
 
 import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
@@ -316,12 +318,15 @@ protected URL createRelativeURL(String relativePath) throws MalformedURLExceptio
 	}
 
 	/**
-	 * This implementation returns the name of the file that this URL refers to.
+	 * This implementation returns the URL-decoded name of the file that this URL
+	 * refers to.
 	 * @see java.net.URL#getPath()
+	 * @see java.net.URLDecoder#decode(String, java.nio.charset.Charset)
 	 */
 	@Override
 	public String getFilename() {
-		return StringUtils.getFilename(getCleanedUrl().getPath());
+		String filename = StringUtils.getFilename(getCleanedUrl().getPath());
+		return URLDecoder.decode(filename, StandardCharsets.UTF_8);
 	}
 
 	/**

spring-core/src/test/java/org/springframework/core/io/ResourceTests.java

@@ -24,6 +24,7 @@
 import java.io.InputStreamReader;
 import java.net.HttpURLConnection;
 import java.net.MalformedURLException;
+import java.net.URI;
 import java.net.URISyntaxException;
 import java.net.URL;
 import java.nio.ByteBuffer;
@@ -59,7 +60,6 @@
  */
 class ResourceTests {
 
-
 	@ParameterizedTest(name = "{index}: {0}")
 	@MethodSource("resource")
 	void resourceIsValid(Resource resource) throws Exception {
@@ -272,6 +272,22 @@ void filenameIsExtractedFromFilePath() throws Exception {
 			assertThat(new UrlResource("file:\\dir/test.txt?argh").getFilename()).isEqualTo("test.txt");
 		}
 
+		@Test
+		void filenameContainingHashTagIsExtractedFromFilePathUnencoded() throws Exception {
+			String unencodedPath = "/dir/test#1.txt";
+			String encodedPath = "/dir/test%231.txt";
+
+			URI uri = new URI("file", unencodedPath, null);
+			URL url = uri.toURL();
+			assertThat(uri.getPath()).isEqualTo(unencodedPath);
+			assertThat(uri.getRawPath()).isEqualTo(encodedPath);
+			assertThat(url.getPath()).isEqualTo(encodedPath);
+
+			UrlResource urlResource = new UrlResource(url);
+			assertThat(urlResource.getURI().getPath()).isEqualTo(unencodedPath);
+			assertThat(urlResource.getFilename()).isEqualTo("test#1.txt");
+		}
+
 		@Test
 		void factoryMethodsProduceEqualResources() throws Exception {
 			Resource resource1 = new UrlResource("file:core/io/Resource.class");