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(\'.\');
Strin         


        

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

Maybe you could use String#split

To answer your comment:

I'm not sure if there can be more than one . in a filename, but whatever, even if there are more dots you can use the split. Consider e.g. that:

String input = "boo.and.foo";

String[] result = input.split(".");

This will return an array containing:

{ "boo", "and", "foo" }

So you will know that the last index in the array is the extension and all others are the base.