Your regex is fine for matching the input string. Your problem is that you used split(), which expects a regex with a totally different purpose. For split(), the regex you give it matches the delimiters (separators) that separate parts of the input; they don't match the entire input. Thus, in a different situation (not your situation), you could say
String[] parts = s.split("[\\- ]");
The regex matches one character that is either a dash or a space. So this will look for dashes and spaces in your string and return the parts separated by the dashes and spaces.
To use your regex to match the input string, you need something like this:
String filename = "01. Kodaline - Autopilot.mp3";
String regex = "^(.*)\\.(.*)\\-(.*)\\.(mp3|flac)";
Pattern pattern = Pattern.compile(regex);
Matcher matcher = pattern.matcher(filename);
String[] metadata = new String[4];
if (matcher.find()) {
metadata[0] = matcher.group(1); // in real life I'd use a loop
metadata[1] = matcher.group(2);
metadata[2] = matcher.group(3);
metadata[3] = matcher.group(4);
// the rest of your code
}
which sets metadata to the strings "01", " Kodaline ", " Autopilot", "mp3", which is close to what you want except maybe for extra spaces (which you can look for in your regex). Unfortunately, I don't think there's a built-in Matcher function that returns all the groups in one array.
(By the way, in your regex, you don't need the backslashes in front of -, but they're harmless, so I left them in. The - doesn't normally have a special meaning, so it doesn't need to be escaped. Inside square brackets, however, a hyphen is special, so you should use backslashes if you want to match a set of characters and a hyphen is one of those characters. That's why I used backslashes in my split example above.)
