public String download(String ftpUrl,String sfzh){

        FTPClient ftpClient = new FTPClient();

        InputStream inputStream = null;

        String re=null;

        try {

            ftpClient.connect(ftp_ip,ftp_port);

            ftpClient.login(ftp_username, ftp_password);

            ftpClient.setFileType(FTPClient.BINARY_FILE_TYPE);

            //是否成功登录服务器

            int reply = ftpClient.getReplyCode();

            if (!FTPReply.isPositiveCompletion(reply)) {

                ftpClient.disconnect();

            }

            //跳转到指定目录

            ftpClient.changeWorkingDirectory(ftpUrl);

            //5.遍历下载的目录

            FTPFile[] fs = ftpClient.listFiles();

            for (FTPFile ff : fs){

                //解决中文乱码问题，两次解码

                byte[] bytes=ff.getName().getBytes("iso-8859-1");

                String fileName=new String(bytes,"utf-8");

                if(sfzh.equals(fileName)){

                    inputStream = ftpClient.retrieveFileStream(fileName);

                }

            }

            if (inputStream != null) {

                byte[] data=null;

                data=new byte[inputStream.available()];

                BASE64Encoder encoder=new BASE64Encoder();

                re=encoder.encode(data);

            }

        } catch (Exception e) {

            e.printStackTrace();

        }finally{

            if(ftpClient.isConnected()){

                try{

                    ftpClient.disconnect();

                }catch(IOException e){

                    e.printStackTrace();

                }

            }

            if(null != inputStream){

                try {

                    inputStream.close();

                } catch (IOException e) {

                    e.printStackTrace();

                }

            }

        }

        return re;

    }