如何使用 ftpclient java 从 ftp 下载前 20 个文件

Question

假设 FTP 位置有 100 个文件。每次调用该函数时，我想从 100 个文件中下载 20 个文件。当我调用 readFTP 函数时，我该如何实现？

ReadFTPread(String host, String userName, String password,String ftpDirectory,String downloadDir)

public static String read(String host, String userName, String password,String ftpDirectory,String downloadDir) {
    Logger logger = Logger.getLogger("LCAlertLog");
    // get an ftpClient object
    FTPClient ftpClient = new FTPClient();

    FileOutputStream fos = null;

    String fileName = "";

    try {

        ftpClient.connect(host);

        //boolean login = ftpClient.login(username,password);
        boolean login = ftpClient.login(userName, password);
        if (login) {
            //Logger.info(Connection established.####..");
            ftpClient.changeWorkingDirectory(ftpDirectory);

            int  returnCode = ftpClient.getReplyCode();
            logger.info("### FTP RETURN CODE for change to: "+ ftpDirectory+" :"+returnCode);
            ////System.out.println("### FTP RETURN CODE for change to: "+ ftpDirectory+" :"+returnCode);

            FTPFile[] files = ftpClient.listFiles();

            for (FTPFile file : files) {
                if (file.getType() == FTPFile.FILE_TYPE) {

                    logger.info("File Name: "+ file.getName());

                    fileName = file.getName();

                    Date lastModified = file.getTimestamp().getTime();

                    Calendar today = Calendar.getInstance();
                    // Subtract 1 day to get yesterday
                    // today.add(Calendar.DATE, -8);
                    today.add(Calendar.DATE, -0); // TODAYS DATE , put -1 to
                                                    // get YESTERDAY

                    Date yesterday = new java.sql.Date(
                            today.getTimeInMillis());

                    int flag = 0;
                    int searchDateRange = 1;

                    if (searchDateRange == 1) {

                        fos = new FileOutputStream(downloadDir + fileName);
                        boolean download = ftpClient.retrieveFile(fileName,fos);
                        logger.info("#### IS DOWNLOAD: "+download);
                        ////System.out.println("#### IS DOWNLOAD: "+download);
                        if (download) {
                            String existingFilepath = ftpDirectory;
                            String newFilepath = "backup/";
                            //ftpClient.makeDirectory(newFilepath)
                        //  //System.out.println("### FILE Current: "+existingFilepath+fileName+"### FILE NEW :"+newFilepath+fileName);

                            /*  ftpClient.rename(existingFilepath+fileName,newFilepath+fileName);*/

                            ByteArrayOutputStream outputStream = new ByteArrayOutputStream();

                            ftpClient.retrieveFile(fileName, outputStream);
                            InputStream is = new ByteArrayInputStream(outputStream.toByteArray());
                            //now, store this stream to backup directory. First we need to change working directory to backup directory.

                            // assuming backup directory is with in current working directory
                            ftpClient.setFileType(FTP.BINARY_FILE_TYPE);//binary files
                            ftpClient.changeWorkingDirectory(newFilepath);


                             returnCode = ftpClient.getReplyCode();
                             logger.info("### FTP RETURN CODE for : "+newFilepath+" :"+returnCode);
                             ////System.out.println("### FTP RETURN CODE for : "+newFilepath+" :"+returnCode);
                                if (returnCode == 550) {
                                    logger.warn("### Change dir failed return code"+returnCode);
                                    ////System.out.println("Change dir failed");
                                }

                            //this overwrites the existing file
                                logger.info("#### FTP CLIENT STORE FILE: "+ftpClient.storeFile(fileName, is));
                            ////System.out.println("#### FTP CLIENT STORE FILE: "+ftpClient.storeFile(fileName, is));
                            ftpClient.changeWorkingDirectory("../");
                            logger.info("### FTP RETURN CODE for Previous Dir :"+returnCode);
                            ////System.out.println("### FTP RETURN CODE for Previous Dir :"+returnCode);
                            ftpClient.deleteFile(fileName);
                            returnCode = ftpClient.getReplyCode();
                            logger.info("### FTP RETURN CODE for delete : "+ftpDirectory + fileName+" :"+returnCode);
                        //  //System.out.println("### FTP RETURN CODE for delete : "+ftpDirectory + fileName+" :"+returnCode);
                            //if you don't want to overwrite it use storeUniqueFile

                            fos.close();
                        }

                    } else if (searchDateRange == 0) {

                    }

                }
            }

            // logout the user, returned true if logout successfully
            boolean logout = ftpClient.logout();
            if (logout) {
                // //Logger.info(Connection close...");
            }
        } else {
            logger.warn("Connection failed ");
        }
        // testing.closeFile();

    } catch (SocketException e) {

        logger.warn("EXCEPTION ",e);
        return "Socket Exception";
    } catch (IOException e) {
        logger.warn("EXCEPTION ",e);

        return "IOException";
    } catch (Exception e) {
        logger.warn("EXCEPTION ",e);
        return "exception";
    }

    return "Success";
}

Answer 1

据我了解，您想在第一次通话中下载前 20 个项目。在第二次通话中，您想下载第 20 到第 40 项，就这样。

    FTPFile[] files = ftpClient.listFiles();

此方法是列出 FTP 中的所有项目。因此，您必须选择要下载的项目。

我的建议你可以调用函数，如 ;

    public static String read(String host, String userName, String password,String ftpDirectory,String downloadDir, int index) {
            ...
            for (int i = index; i<index+20; i++) {
                    FTPFile file = files[index];//you have the file

例如，您可以传递索引值 = 0,20,40,60,80；

           for(int i = 0;i<5;i++){
              read(userName,password,ftpDirectory,downloadDir,i*20);
           }

Answer 2

您可以使用迭代变量，例如。 G。一个我，每次你下载一个特定的文件时，你计算 i 加一，如果 i >= 20 则中止该功能。