Question

For example, I wanted to get the file Extension from the file URL using the function below:

File name:

Greatest Hits - Lenny Kravitz (Booklet 01) [2000].jpg

Url of the file:

String url = "/mnt/sdcard/mydev/Greatest Hits - Lenny Kravitz (Booklet 01) [2000].jpg";

Function call:

String extension = MimeTypeMap.getFileExtensionFromUrl(url);

But I’m getting an exception on the function call. Is this a bug or a feature?

It works fine for file names that don’t contain that many foreign characters (such as paranthesis).

Is the function buggy? Am I missing something? How am I supposed to differentiate a bug from a feature? I’ve read the function description and it should work properly.

Do you personally use it in your projects? It doesn’t seem reliable.

Answer 1

When I test your code, no exception is thrown for me. Though the proper file extension “jpg” is not returned. I would not advise using MimeTypeMap. An easy way to obtain the file extension instead is as follows:

String file = "/mnt/sdcard/mydev/Greatest Hits - Lenny Kravitz (Booklet 01) [2000].jpg";
String exten = "";

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

As to why MimeTypeMap.getFileExtensionFromUrl(url) fails? It’s expecting a properly formated URL String, which yours is not. You should first encode it using URLEncoder. For example:

String url = "/mnt/sdcard/mydev/Greatest Hits - Lenny Kravitz (Booklet 01) [2000].jpg";
url = URLEncoder.encode(url, "UTF-8");

This should allow MimeTypeMap.getFileExtensionFromUrl(url) to work properly but unfortunately it still doesn’t. Why? URLEncoder will change all spaces to a ‘+’ sign and getFileExtensionFromUrl considers that an invalid character. This part, IMHO, is a bug.

From my experience, most people don’t use this method. In fact, I never heard of it until you posted this question. Probably because finding a file extension is fairly trivial and most people write code similar to what I posted above.