Java getting file extension without substring

Question

How do I get file extension in Java without using that silly lastIndexOf('.') etc.?

possible duplicate of [How do I trim a file extension from a String in Java?](http://stackoverflow.com/questions/941272/how-do-i-trim-a-file-extension-from-a-string-in-java) — pb2q, Jul 22 '12 at 20:23
A little background into why `lastindexof` isn't what you want or isn't working for you - sure I know this is approach has issues as well, but a little understanding as to why you are looking for another approach might help. — MadProgrammer, Jul 22 '12 at 21:08
I guess the other libraries also would follow the same method. In fact FileNameUtils use the same mechanism. But i wonder why you dont want that. Do you think it will fail for some cases. If so can u state an example of failure with this case? — Vivek, Jan 29 '14 at 07:13

score 15 · Accepted Answer · edited Mar 11 '13 at 21:03

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The apache Commons library has FilenameUtils.getExtension().

You can look over the source starting here, and FilenameUtils.

At least look over their implementation. It's pretty simple, they handle dir.ext/file correctly, and to handle something like file.tar.gz you'll need a special case if you want to extract .tar.gz rather than just .gz.

edited Mar 11 '13 at 21:03

sikander

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answered Jul 22 '12 at 20:18

pb2q

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I had interpreted that he wanted the file extension itself, not the name without the extension. There is still a method for that (`getExtension`), but read what it does: *"returns the textual part of the filename after the last dot."* That's exactly what he's already doing; there's no point in adding an entire library/dependency just for the same functionality (unless he's already using Apache Commons). – Jon Newmuis Jul 22 '12 at 20:21
@JonathanNewmuis that is, right about my method mixup. I believe that the implementation of `getExtension` is a bit more thorough that simply wrapping a `lastIndexOf`, for reasons that your own answer addresses, and e.g. _dir.ext/file_. – pb2q Jul 22 '12 at 20:28
Unfortunately this is not a standard library, so it is overkill for the probblem, i used lastIndexOf – Yoda Jul 22 '12 at 20:57

score 2 · Answer 2 · answered Jul 22 '12 at 20:18

That's probably the easiest way (also note that depending on the context, it's not necessarily correct, e.g. ".tar.gz").

You could also split the string based on the . character and take the last piece, but that seems just as difficult.

Is there a particular reason why you're trying to avoid substring and lastIndexOf?

score 1 · Answer 3 · answered Nov 14 '13 at 18:35

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Do not want to include external libraries? Use regular expressions:

String extension = filename.replaceAll("^.*\\.([^.]+)$", "$1");

answered Nov 14 '13 at 18:35

Paul Vargas

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Entea · Answer 4 · 2014-10-14T09:02:41.830

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With guava

Files.getFileExtension("some.txt")

edited Oct 14 '14 at 09:02

answered Oct 03 '14 at 06:49

Entea

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I am afraid there is no such method in [jdk8](http://docs.oracle.com/javase/8/docs/api/java/nio/file/Files.html), I guess you mean google's [guava](http://docs.guava-libraries.googlecode.com/git/javadoc/com/google/common/io/Files.html#getFileExtension%28java.lang.String%29) – A4L Oct 12 '14 at 12:23
@A4L thanks for pointing this out, I got confused by java.lang package of this class ☺ – Entea Oct 12 '14 at 12:47

Java getting file extension without substring

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