Normalize URIs returned from FileSystemResource.getURI()

Prior to this commit, if a FileSystemResource was created from a
java.nio.file.Path or java.nio.file.FileSystem, the URI returned from
getURI() was based on the semantics of Path#toUri() which always
includes the "authority component" (i.e., "//") after the scheme (e.g.,
"file://..."). In contrast, if a FileSystemResource is created from a
java.io.File or String, the URI returned from getURI() never includes
the "authority component" due to the semantics of File#toURI().

Consequently, invoking myFileSystemResource.getURI().toString() could
result in "file:/my/path" or "file:///my/path", depending on how the
FileSystemResource was created.

This behavior is not new; however, recent changes in
PathMatchingResourcePatternResolver -- which result in a
FileSystemResource being created from a java.nio.file.Path instead of
from a java.io.File -- make this difference more noticeable to users
and may in fact surface as a breaking change.

To address that issue, this commit revises the implementation of
FileSystemResource.getURI() by normalizing any `file:` URIs that it
returns. Effectively, URIs like "file:///my/path" will now take the
form "file:/my/path".

See gh-29163
Closes gh-29275

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2022 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.
@@ -22,6 +22,7 @@ import java.io.IOException;
 import java.io.InputStream;
 import java.io.OutputStream;
 import java.net.URI;
+import java.net.URISyntaxException;
 import java.net.URL;
 import java.nio.channels.FileChannel;
 import java.nio.channels.ReadableByteChannel;
@@ -34,6 +35,7 @@ import java.nio.file.StandardOpenOption;
 
 import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
+import org.springframework.util.ResourceUtils;
 import org.springframework.util.StringUtils;
 
 /**
@@ -48,6 +50,7 @@ import org.springframework.util.StringUtils;
  * interactions via NIO.2, only resorting to {@link File} on {@link #getFile()}.
  *
  * @author Juergen Hoeller
+ * @author Sam Brannen
  * @since 28.12.2003
  * @see #FileSystemResource(String)
  * @see #FileSystemResource(File)
@@ -226,7 +229,23 @@ public class FileSystemResource extends AbstractResource implements WritableReso
 	 */
 	@Override
 	public URI getURI() throws IOException {
-		return (this.file != null ? this.file.toURI() : this.filePath.toUri());
+		if (this.file != null) {
+			return this.file.toURI();
+		}
+		else {
+			URI uri = this.filePath.toUri();
+			// Normalize URI? See https://github.com/spring-projects/spring-framework/issues/29275
+			String scheme = uri.getScheme();
+			if (ResourceUtils.URL_PROTOCOL_FILE.equals(scheme)) {
+				try {
+					uri = new URI(scheme, uri.getPath(), null);
+				}
+				catch (URISyntaxException ex) {
+					throw new IllegalStateException("Failed to normalize URI: " + uri, ex);
+				}
+			}
+			return uri;
+		}
 	}
 
 	/**

spring-core/src/test/java/org/springframework/core/io/support/PathMatchingResourcePatternResolverTests.java

@@ -23,7 +23,6 @@ import java.nio.file.Path;
 import java.util.Arrays;
 import java.util.List;
 
-import org.junit.jupiter.api.Disabled;
 import org.junit.jupiter.api.Nested;
 import org.junit.jupiter.api.Test;
 
@@ -108,7 +107,6 @@ class PathMatchingResourcePatternResolverTests {
 				assertExactSubPaths(pattern, pathPrefix, "resource#test1.txt", "resource#test2.txt");
 			}
 
-			@Disabled("Disabled until gh-29275 is addressed")
 			@Test
 			void usingFileProtocolAndAssertingUrlAndUriSyntax() throws Exception {
 				Path testResourcesDir = Path.of("src/test/resources").toAbsolutePath();