Convert between URL and windows filename (Java)?

Question

Is there a standard/good way of converting between urls and windows filenames, in Java?

I am trying to download files, but I want the windows filename to be convertible back to the original filename. Note that the query portion of the url is vital, as I will be downloading different pages that differ only in query.

My current hacky solution is to replace illegal characters (such as '?') with a specific string (such as 'QQ'), but this makes conversion back to url less transparent. Is there a better way?

Answer 1

You could do worse than use URLEncoder to encode the URL:

String url = "http://172.0.0.1:80/foo/bar/baz.txt?black=white";
String filename = URLEncoder.encode(url, "UTF-8");
File file = new File(filename);

The filename becomes the legal win32 name:

http%3A%2F%2F172.0.0.1%3A80%2Ffoo%2Fbar%2Fbaz.txt%3Fblack%3Dwhite

This is a reversible operation:

String original = URLDecoder.decode(filename, "UTF-8");

Answer 2

The java.io.File class takes a URI &| filename as a constructor, but contains toURI() & toURL() methods as well as getName() & getPath(). I assume this would be a valid conversion for you?

Answer 3

But is it possible to encode url to filename at all? I mean, can there be the 100% valid solution? I think that converting url to filename is the wrong idea in general, because of different limitations set on urls and filenames:

Max filename length (NTFS filesystem, Unicode, using UTF-16 encoding) - 255

Max URL length (using UTF-8 encoding?) - 2000 chars