CommonsMultipartFile removes mixed separator paths from original filename

Issue: SPR-13662

spring-web/src/main/java/org/springframework/web/multipart/commons/CommonsMultipartFile.java

@@ -78,12 +78,13 @@ public class CommonsMultipartFile implements MultipartFile, Serializable {
 			// Should never happen.
 			return "";
 		}
+
 		// Check for Unix-style path
-		int pos = filename.lastIndexOf("/");
-		if (pos == -1) {
+		int unixSep = filename.lastIndexOf("/");
 		// Check for Windows-style path
-			pos = filename.lastIndexOf("\\");
-		}
+		int winSep = filename.lastIndexOf("\\");
+		// Cut off at latest possible point
+		int pos = (winSep > unixSep ? winSep : unixSep);
 		if (pos != -1)  {
 			// Any sort of path separator found...
 			return filename.substring(pos + 1);

spring-web/src/test/java/org/springframework/web/multipart/commons/CommonsMultipartResolverTests.java

@@ -383,9 +383,9 @@ public class CommonsMultipartResolverTests {
 					MockFileItem fileItem1x = new MockFileItem(
 						"field1", "type1", empty ? "" : "field1.txt", empty ? "" : "text1");
 					MockFileItem fileItem2 = new MockFileItem(
-						"field2", "type2", empty ? "" : "C:/field2.txt", empty ? "" : "text2");
+						"field2", "type2", empty ? "" : "C:\\mypath/field2.txt", empty ? "" : "text2");
 					MockFileItem fileItem2x = new MockFileItem(
-						"field2x", "type2", empty ? "" : "C:\\field2x.txt", empty ? "" : "text2");
+						"field2x", "type2", empty ? "" : "C:/mypath\\field2x.txt", empty ? "" : "text2");
 					MockFileItem fileItem3 = new MockFileItem("field3", null, null, "value3");
 					MockFileItem fileItem4 = new MockFileItem("field4", "text/html; charset=iso-8859-1", null, "value4");
 					MockFileItem fileItem5 = new MockFileItem("field4", null, null, "value5");