参考, 注意最后的评论

FTP Client使用的是Apache Commons Net 3.3

    /**
     * 检查FTP上指定文件是否存在
     * @param remoteFilePartNameList 文件路径
     * @throws BusinessException
     * @throws IOException
     */
    private void checkFtpFileExist(List<String> remoteFilePartNameList) throws BusinessException, IOException {
        FTPClient ftp = new FTPClient();
        String serverIP = "1.1.1.1";
        String serverUserName = "user";
        String serverPassword = "pwd";
        try {
            ftp.connect(serverIP);
            ftp.login(serverUserName, serverPassword);

            if (FTPReply.isPositiveCompletion(ftp.getReplyCode())) {
                ftp.enterLocalPassiveMode();
                ftp.setFileType(FTP.BINARY_FILE_TYPE);
                StringBuilder sb = null;
                
                for (String remoteFileName : remoteFilePartNameList) {
                    InputStream inputStream = ftp.retrieveFileStream(remoteFileName);
                    if (inputStream == null || ftp.getReplyCode() == 550) {
                        // 文件不存在 
                        if (sb == null) {
                            sb = new StringBuilder();
                        }
                        String[] strings = StringUtils.split(remoteFileName, Constants.SLASH);
                        sb.append(strings[strings.length - 1]).append(", ");
                    }
                    
                    if (inputStream != null) {
                        inputStream.close();
                        ftp.completePendingCommand(); // 必须执行，否则在循环检查多个文件时会出错
                    }
                }
                
                if (sb != null && sb.length() > 2) {
                    sb.setLength(sb.length() - 2);
                    String notfoundReportPaymentIdStr = sb.toString();
                    log.error("FTP SERVER上未找到以下文件[" + notfoundReportPaymentIdStr + "]");
                    String exceptionMessage = i18nServiceImpl.queryValue("E374", "文件{0}不存在！");
                    throw new BusinessException(StringUtils.replace(exceptionMessage, "{0}", notfoundReportPaymentIdStr));
                }
            }
            else {
                log.error("连接FTP SERVER失败，SERVER IP[" + serverIP + "], USER NAME[" + serverUserName + "], Ftp response:" + ftp.getReplyString());
                ftp.disconnect();
                throw new BusinessException(i18nServiceImpl.queryValue("E373", "连接FTP失败！"));
            }
            ftp.logout();
        }
        catch (IOException e) {
            log.error("连接FTP SERVER失败，SERVER IP[" + serverIP + "], USER NAME[" + serverUserName + "]", e);
            throw e;
        }
        finally {
            if (ftp.isConnected()) {
                try {
                    ftp.disconnect();
                }
                catch (IOException ioe) {
                    // do nothing
                }
            }
        }
    }