Regex to get filename with or without extension from a path

Question

Looking for a regex to extract out the filename part excluding the extension from a path in this code

String filename = fullpath.replaceFirst(regex, "$1")

e.g. for starter, here is the most simple case and what I have done:

Here are some more advance cases that I need help with:

Edited: There is no actual file here and the fullpath does not lead to any file. It is coming from a URL request.

cause you say that a folder is no file. Once you filter out the folders, it works 100%. But folders are files and have names too tho. Also the extension is usually part of the name — XtremeBaumer, Nov 15 '19 at 08:16
@XtremeBaumer I am not too sure what you are talking about? And I tried your code, it did not give correct answers. And I did not mention folder anywhere, why are you saying folder? — user1589188, Nov 15 '19 at 08:21
`/path_a/path.b/` is a valid path to a folder instead of a file. Yet it still has a name — XtremeBaumer, Nov 15 '19 at 08:25
https://stackoverflow.com/a/990408/7109162 + `new File(fullpath).getName()` — XtremeBaumer, Nov 15 '19 at 08:25
@XtremeBaumer you confuse me a lot here. I said I tried your code, it did not give correct result already, why are you still promoting it? `new File("/path/filename.ext").getName()` gives "filename.ext" not "filename" that I required in the question. — user1589188, Nov 15 '19 at 08:29
Possible duplicate of [How do I trim a file extension from a String in Java?](https://stackoverflow.com/questions/941272/how-do-i-trim-a-file-extension-from-a-string-in-java) — XtremeBaumer, Nov 15 '19 at 08:35
@XtremeBaumer I read the link, but no I am not dealing with actual file here. Its an incoming request in URL that I need to extract the filename part from it. — user1589188, Nov 15 '19 at 08:40

revo · Accepted Answer · 2019-11-15T08:38:15.060

9

The following regex will match desired parts:

^(?:.*\/)?([^\/]+?|)(?=(?:\.[^\/.]*)?$)

Explanation:

^ Match start of the line
(?: Start of a non-capturing group
- .*\/ Match up to last / character
)? End of the non-capturing (optional)
([^\/]+?|) Capture anything but / ungreedily or nothing
(?= Start of a positive lookahead
- (?:\.[^\/.]*)? Match an extension (optional)
- $ Assert end of the line
) End of the positive lookahead

but if you are dealing with a multi-line input string and need a bit faster regex try this one instead (with m flag on) :

^(?:[^\/\r\n]*\/)*([^\/\r\n]+?|)(?=(?:\.[^\/\r\n.]*)?$)

Filename would be captured in the first capturing group.

edited Nov 15 '19 at 08:38

answered Nov 15 '19 at 08:28

revo

Thanks a lot, it seems yours is working in the demo, but I can't put it in my java code, it seems the syntax is a bit different? – user1589188 Nov 15 '19 at 08:38
2

@user1589188 Yes, where is one backslash you need two. – revo Nov 15 '19 at 08:39
Yes I did that. Please help me out here `"/path/filename.ext".replaceFirst("^(?:.*\\/)?([^\\/]+?|)(?=(?:\\.[^\\/.]*)?$)", "$1")` this does not print "filename" but "filename.ext". What am I doing wrong? – user1589188 Nov 15 '19 at 08:46
2

@user1589188 You shouldn't use a replacement method here but if you have to, you should change positive lookahead to a simple matching cluster: `"/path/filename.ext".replaceFirst("^(?:.*\\/)?([^\\/]+?|)(?:\\.[^\\/.]*)?$", "$1")` – revo Nov 15 '19 at 08:52
2

@user1589188 This also can be helpful https://regex101.com/r/9FUtDb/1/codegen?language=java – revo Nov 15 '19 at 08:53
Thank you, the code in the comment did it. Although I don't understand why the difference, but there you go, points for you! – user1589188 Nov 15 '19 at 08:54
3

Very impressive ! Great job @revo ! That's working well and your explanation are perfect, thank you. – Gosfly Nov 15 '19 at 09:30

score 3 · Answer 2 · answered Nov 15 '19 at 08:17

3

You can use the getName() function on a File object and then remove the extension using a Regex and you can check if it's a file too:

File file = new File(fullpath);
if (file.isFile()) return file.getName().replace("\..*", "");
else return "";

answered Nov 15 '19 at 08:17

SteapStepper69

1

Thanks but I am not working on actual files. In fact, I am dealing with a request URL, so there is no file for me to check. – user1589188 Nov 15 '19 at 08:31
No worries, thanks for the input. Should be helpful to others if they have files to work on. – user1589188 Nov 15 '19 at 08:57
@XtremeBaumer would the `isFile()` check actually work with a path that is non-existent on the file system? – SteapStepper69 Nov 15 '19 at 11:16
If the file doesn't actually exists, then `isFile()` and `isDirectory()` both return `false` – XtremeBaumer Nov 15 '19 at 11:20
But then the OP is right, if he doesn't have the file on disk, this method won't work. – SteapStepper69 Nov 15 '19 at 12:15

score 3 · Answer 3 · edited Nov 15 '19 at 08:40

3

Use the path file (String pathFile) to get the name file with extension and remove it with FilenameUtils.removeExtension

String nameDocument = pathFile.substring(pathFile.lastIndexOf("/") + 1);

String fileNameWithOutExt = FilenameUtils.removeExtension(nameDocument);

edited Nov 15 '19 at 08:40

geisterfurz007

answered Nov 15 '19 at 08:26

Hey thank you. I guess it is helpful for others. But in my case, it seems "/path/.filename" does not give ".filename" using that util. – user1589188 Nov 15 '19 at 08:56

3 Answers3