Check if file with "ftp" url exists using java

Check if file with "ftp" url exists using java

please, could anyone tell me, how can i check if file exists on URL where
is only FTP protocol? Im using this code:
public boolean exists(String URLName) throws IOException {
input = null;
boolean result = false;
try {
input = new URL(URLName).openStream();
System.out.println("SUCCESS");
result = true;
} catch (Exception e) {
System.out.println("FAIL");
} finally {
if (input != null) {
input.close();
input = null;
}
}
return result;
}
It doesnt work when i send there more then one or two, it just sais
sun.net.ftp.FtpProtocolException: Welcome message: 421 Too many
connections (2) from this IP
at sun.net.ftp.FtpClient.openServer(FtpClient.java:490)
at sun.net.ftp.FtpClient.openServer(FtpClient.java:475)
at
sun.net.www.protocol.ftp.FtpURLConnection.connect(FtpURLConnection.java:270)
at
sun.net.www.protocol.ftp.FtpURLConnection.getInputStream(FtpURLConnection.java:352)
at java.net.URL.openStream(URL.java:1010)
at bibparsing.PDFImage.exists(PDFImage.java:168)
at bibparsing.PDFImage.main(PDFImage.java:189)
It works great when the protocol is HTTP. I mean adresses like:
http://stackoverflow.com/ftp://cmp.felk.cvut.cz/pub/cmp/articles/chum/Chum-TR-2001-27.pdf
http://stackoverflow.com/ftp://cmp.felk.cvut.cz/pub/cmp/articles/martinec/Kamberov-ISVC2006.pdf
and something like that