Sometimes it is useful to be able to read from or write to the FTP server as if it were a InputStream or OutputStream. This is possible using FTPInputStream and FTPOutputStream. These classes directly subclass Java's InputStream and OutputStream, and can be used in exactly the same manner. 

An instance of FTPClient or a subclass must be supplied to the stream's constructor. Currently SSHFTPClient is not supported, but will be in a future version. 

An instance of FTPInputStream or FTPOutputStream can only be used for one data transfer. It is essential that the stream is closed when the transfer is complete, even if an exception was thrown. Otherwise, server acknowledgements may get out of order, and the connection will need to be closed.

All of the stream's transfer parameters are taken from the FTPClient instance that is supplied to the constructor. For example, if the stream is to be a binary mode transfer, binary mode must be set in the FTPClient instance before it is supplied to the constructor.  

try {
    out = new BufferedOutputStream(new FileOutputStream("myfile.zip"));
    while ((count = in.read(chunk)) >= 0) {
        out.write(chunk, 0, count);
    }
}
finally {
    try {
        in.close();
    }
    catch (Exception ex) {
        ex.printStackTrace();
    }
    if (out != null) {
        try {
            out.close();
        }
        catch (Exception e) {
            e.printStackTrace();
        }
    }
}

Note that care must be taken via a finally block to ensure that the FTP stream is closed (and, of course, the file stream). 

FTPInputStream can be especially useful when a large file is being downloaded and the stream needs to be processed as it arrives. For example, if an XML file was being downloaded, a SAX parser could parse the stream as data arrived.