How do i get the file extension of a file in Java?

Question

Just to be clear, I'm not looking for the MIME type.

Let's say i have the input: "/path/to/file/foo.txt"

I'd like a way to break this input up, specifically into ".txt" for the extension. Is there any built in ways to do this in Java? I'm still new and would like to avoid writing my own parser... :)

Thanks!

Answer 1

Do you really need a "parser" for this?

String extension = "";

int i = fileName.lastIndexOf('.');
if (i > 0) {
    extension = fileName.substring(i+1);
}

Assuming that you're dealing with simple Windows-like file names, not something like "archive.tar.gz".

Btw, for the case that a directory may have a '.', but the filename itself doesn't (like /path/to.a/file), you can do

String extension = "";

int i = fileName.lastIndexOf('.');
int p = Math.max(fileName.lastIndexOf('/'), fileName.lastIndexOf('\\');

if (i > p) {
    extension = fileName.substring(i+1);
}

Answer 2

// Modified from EboMike's answer

String extension = "/path/to/file/foo.txt".substring("/path/to/file/foo.txt".lastIndexOf('.'));

extension should have ".txt" in it when run.

Answer 3

How about JFileChooser? It is not straightforward as you will need to parse its final output...

JFileChooser filechooser = new JFileChooser();
File file = new File("your.txt");
System.out.println("the extension type:"+filechooser.getTypeDescription(file));

which is a MIME type...

OK...I forget that you don't want to know its MIME type.

Interesting code in the following link: http://download.oracle.com/javase/tutorial/uiswing/components/filechooser.html

/*
 * Get the extension of a file.
 */  
public static String getExtension(File f) {
    String ext = null;
    String s = f.getName();
    int i = s.lastIndexOf('.');

    if (i > 0 &&  i < s.length() - 1) {
        ext = s.substring(i+1).toLowerCase();
    }
    return ext;
}

Related question: http://stackoverflow.com/questions/941272/how-do-i-trim-a-file-extension-from-a-string-in-java