The URL: ftp://user@password@server/file
will cause the constructor for FtpURLConnection to throw
StringIndexOutOfBoundsException. This was not expected.

The code assumes that if a user is specified in the URL
then there will be a colon used to specify the password.

     public FtpURLConnection(URL url) {
         super(url);
         host = url.getHost();
         String userInfo = url.getUserInfo();
 
         if (userInfo != null) { // get the user and password
             int delimiter = userInfo.indexOf(':');
             user = userInfo.substring(0, delimiter++);
             password = userInfo.substring(delimiter);
         }
     }

Bug 4450673 has a stack trace of this problem.

% java -version
java version "1.3.0"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.3.0)
Java HotSpot(TM) Client VM (build 1.3.0, mixed mode)