java连接ftp读取图片并转Base64

public String download(String ftpUrl,String sfzh){
        //ftpUrl :文件夹路径  afzh:图片路径
        FTPClient ftpClient = new FTPClient();
        InputStream inputStream = null;
        String re=null;
        try {
            ftpClient.connect(ftp_ip,ftp_port);//ip地址，端口号
            ftpClient.login(ftp_username, ftp_password);//账户，密码
            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;
                   ByteArrayOutputStream outStream =new ByteArrayOutputStream();
                   data=new byte[inputStream.available()];
                   int len=0;
                   while((len=inputStream.read(data))!=-1){
                       outStream.write(data,0,len);
                   }
                   data=outStream.toByteArray();
                   Encoder encoder=Base64.getEncoder();
                   re=encoder.encodeToString(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;
    }
　　

<dependency>
   <groupId>commons-net</groupId>
   <artifactId>commons-net</artifactId>
  <version>3.6</version>
</dependency>