Java: splitting the filename into a base and extension

Question

Is there a better way to get file basename and extension than something like

File f = ... String name = f.getName(); int dot = name.lastIndexOf('.'); String base = (dot == -1) ? name : name.substring(0, dot); String extension = (dot == -1) ? "" : name.substring(dot+1); 

Answer 1

I know others have mentioned String.split, but here is a variant that only yields two tokens (the base and the extension):

String[] tokens = fileName.split("\\.(?=[^\\.]+$)"); 

For example:

"test.cool.awesome.txt".split("\\.(?=[^\\.]+$)"); 

Yields:

["test.cool.awesome", "txt"] 

The regular expression tells Java to split on any period that is followed by any number of non-periods, followed by the end of input. There is only one period that matches this definition (namely, the last period).

Technically Regexically speaking, this technique is called zero-width positive lookahead.

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BTW, if you want to split a path and get the full filename including but not limited to the dot extension, using a path with forward slashes,

    String[] tokens = dir.split(".+?/(?=[^/]+$)"); 

For example:

    String dir = "/foo/bar/bam/boozled";      String[] tokens = dir.split(".+?/(?=[^/]+$)");     // [ "/foo/bar/bam/" "boozled" ]  

Answer 2

Old question but I usually use this solution:

import org.apache.commons.io.FilenameUtils;  String fileName = "/abc/defg/file.txt";  String basename = FilenameUtils.getBaseName(fileName); String extension = FilenameUtils.getExtension(fileName); System.out.println(basename); // file System.out.println(extension); // txt (NOT ".txt" !)