sun.net.ftp.FtpClient 获取FTP指定文件大小

private FtpClient ftpClient = new FtpClient();

    public long getFileSize(String filename) {
        long fileSize = -1;
        try {
            ftpClient.openServer("IP","PORT");
            ftpClient.login("USER","PASSWORD");  
            String s = "SIZE " + filename + "\r\n";
            ftpClient.sendServer(s);
            int status = ftpClient.readServerResponse();
            if (status == 213) {
                String msg = ftpClient.getResponseString();
                fileSize = Long.parseLong(msg.substring(3).trim());
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
        return fileSize;
    }