Java FTP file get issue

I have a application that runs as a schedule.It connect to ftp server and get files from remote folder.scheduler runs in every 5min time.Sometimes when there are lot of files in remote location, scheduler runs again while first cycle is running.In such situation some times it download 0 size files even actual file size is greater than 0 in remote location.Does anyone have any idea why this happen?

below is the code to import files.

private void importEDIFiles(String host, String user, String password, String path, String road) {
        try {
            String edi824Path = path + "/" + EDI_824_FOLDER;
            FTPBroker ftpBroker = new FTPBroker(host, user, password, edi824Path);

            FTPClient client = ftpBroker.makeFTPConeection();
            String os = client.getSystemName();
            client.setFileTransferMode(FTP.ASCII_FILE_TYPE);
            File edi824File = null;
            File edi824Filebak = null;
            ArrayList<FTPFile> files;
            try {

                FTPFile[] ftpfiles = client.listFiles();

                logger.info("\t" + ftpfiles.length + " files are in ftp location ");
                if (ftpfiles.length > 0) {
                    files = removeZeroFiles(ftpfiles);
                     for(int x=0;x<files.size();x++){
                         logger.info("name  ---"+files.get(x).getNa开发者_StackOverflow社区me());
                         logger.info("size ----"+files.get(x).getSize());
                     }
                    String ftpFile = null;
                    logger.info("\t" + files.size() + " downloading from " + road + " rail road.");
                    for (int i = 0; i < files.size(); i++) {
                        ftpFile = files.get(i).getName();
                        logger.info("\t" + ftpFile + " is downloading....");
//                        logger.info("\t" + ftpFile + " size ...." + ftpFile.isEmpty());

                        String source = destinationFilePath + pathSeparator + road + pathSeparator + ftpFile;
                        String target = edi_824backupFilePath + pathSeparator + road + pathSeparator + ftpFile;
                        edi824File = new File(source);
                        edi824Filebak = new File(target);
                        FileOutputStream fosout = new FileOutputStream(source);

                        boolean isRetrieved = client.retrieveFile(ftpFile, fosout);
                        logger.debug("isRetrieved : " + isRetrieved);
                        FileUtils.copyFile(edi824File,edi824Filebak);
                        fosout.flush();
                        fosout.close();


                        boolean isDelete = client.deleteFile(ftpFile);
                        logger.debug("isDelete : " + isDelete);

                    }

                } else {
                    logger.info("No files to Pull in the FTP Location for " + user);
                    //throw new RuntimeException("No files to Pull in  FTP Location.");
                }
            } catch (Exception e) {
                logger.error(e,e);
                e.printStackTrace();
            } finally {
                client.logout();
                client.disconnect();


            }


        } catch (Exception ex) {
            logger.error(ex, ex);
            ex.printStackTrace();
        }


    }

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you can use a flag boolean isRunning(), setRunning(boolean ), and synchronize your code so that two or more threads would not run the same method at the same time