how can I get the extension from a file in java?

Question

I have a problem. I have some file without extension and I need discover the extension. How can I do that? I think the only way is to read the file, but i don't know how I can understand the extension. Thanks

@Arpit: They didn't mean to get the file extension, rather recognize the file format without having the extension — wonderb0lt, May 28 '15 at 15:08
You could use [Apache Commons IO](http://stackoverflow.com/a/16202288/284538) for this. — Mike Thomsen, May 28 '15 at 15:09
Perhaps you could edit the question to clarify that you want **to check the file type** of a file, not just substring the extension out of the file name. — nuno, May 28 '15 at 15:14

score 1 · Answer 1 · answered May 28 '15 at 15:09

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To probe the content of a File you could use the nio Java API and the method probeContentType

answered May 28 '15 at 15:09

nuno

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Simulant · Answer 2 · 2015-05-28T15:10:19.347

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If your file has no extension (as you said) you cannot read the extension, because it is not present.

You could read the start of the file and look for some indicators of the content. E.g. most .pdf files start with %PDF-1.5 (or a different version number) in the content.

edited May 28 '15 at 15:10

answered May 28 '15 at 15:09

Simulant

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score 0 · Answer 3 · edited May 23 '17 at 12:21

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I think that the only way is read the magic number of the file...how?

Check this thread Reading the header of a file in java

Hope that help you!

edited May 23 '17 at 12:21

Community

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answered May 28 '15 at 15:09

appersiano

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score 0 · Answer 4 · answered May 28 '15 at 15:10

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Without extension, it's tough to find the format (but it's possible).

Even Windows asks you What to do when you click on Open With.. on a file without extension.

answered May 28 '15 at 15:10

K139

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how can I get the extension from a file in java?

4 Answers4