Add support for double backslashes to StringUtils#cleanPath

Closes gh-32962

Author: sdeleuze

spring-core/src/main/java/org/springframework/util/StringUtils.java

@@ -58,6 +58,7 @@
  * @author Arjen Poutsma
  * @author Sam Brannen
  * @author Brian Clozel
+ * @author Sebastien Deleuze
  * @since 16 April 2001
  */
 public abstract class StringUtils {
@@ -70,6 +71,8 @@ public abstract class StringUtils {
 
 	private static final String WINDOWS_FOLDER_SEPARATOR = "\\";
 
+	private static final String DOUBLE_BACKLASHES = "\\\\";
+
 	private static final String TOP_PATH = "..";
 
 	private static final String CURRENT_PATH = ".";
@@ -690,7 +693,7 @@ public static String applyRelativePath(String path, String relativePath) {
 	 * Normalize the path by suppressing sequences like "path/.." and
 	 * inner simple dots.
 	 * <p>The result is convenient for path comparison. For other uses,
-	 * notice that Windows separators ("\") are replaced by simple slashes.
+	 * notice that Windows separators ("\" and "\\") are replaced by simple slashes.
 	 * <p><strong>NOTE</strong> that {@code cleanPath} should not be depended
 	 * upon in a security context. Other mechanisms should be used to prevent
 	 * path-traversal issues.
@@ -702,7 +705,15 @@ public static String cleanPath(String path) {
 			return path;
 		}
 
-		String normalizedPath = replace(path, WINDOWS_FOLDER_SEPARATOR, FOLDER_SEPARATOR);
+		String normalizedPath;
+		// Optimize when there is no backslash
+		if (path.indexOf('\\') != -1) {
+			normalizedPath = replace(path, DOUBLE_BACKLASHES, FOLDER_SEPARATOR);
+			normalizedPath = replace(normalizedPath, WINDOWS_FOLDER_SEPARATOR, FOLDER_SEPARATOR);
+		}
+		else {
+			normalizedPath = path;
+		}
 		String pathToUse = normalizedPath;
 
 		// Shortcut if there is no work to do

spring-core/src/test/java/org/springframework/util/StringUtilsTests.java

@@ -419,6 +419,7 @@ void cleanPath() {
 		assertThat(StringUtils.cleanPath("file:///c:/some/../path/the%20file.txt")).isEqualTo("file:///c:/path/the%20file.txt");
 		assertThat(StringUtils.cleanPath("jar:file:///c:\\some\\..\\path\\.\\the%20file.txt")).isEqualTo("jar:file:///c:/path/the%20file.txt");
 		assertThat(StringUtils.cleanPath("jar:file:///c:/some/../path/./the%20file.txt")).isEqualTo("jar:file:///c:/path/the%20file.txt");
+		assertThat(StringUtils.cleanPath("jar:file:///c:\\\\some\\\\..\\\\path\\\\.\\\\the%20file.txt")).isEqualTo("jar:file:///c:/path/the%20file.txt");
 	}
 
 	@Test