java - 使用 apache FTPClient 从 FTP 服务器下载文件

Question

我正在使用 apache 的 FTPClient 从 FTP 服务器下载文件。我的情况是 - FTP 服务器可能会失去网络连接，并且可能会保持断开状态最多 1 天。当它重新连接时，文件的下载应该从原来的位置开始。我使用以下代码连接到服务器，然后从服务器下载文件

public void retrieve(String server, int port, String username,
        String password, String remote, String local, int fileType,
        ProgressHandler progressHandler) throws Exception {     
    final FTPClient ftp = new FTPClient();
    Date date = new Date();
    long startTime_ms = date.getTime();
    if (progressHandler != null) {
        ftp.setCopyStreamListener(new FtpCopyStreamListener(progressHandler));
    }

    ftpConnect(server,ftp, port,startTime_ms);


    if(ftp.getReplyCode()==0 || !String.valueOf(ftp.getReplyCode()).startsWith("2")){
        cleanup(ftp, "Could not log into server: " + server, null);
        return;
    }

    boolean loggedIn = false;
    try {
        if (username == null || username.isEmpty()) {
            username = "anonymous";
            password = System.getProperty("user.name") + "@"
                    + InetAddress.getLocalHost().getHostName();
        }
        if (!ftp.login(username, password)) {
            ftp.logout();
            cleanup(ftp, "Could not log into server: " + server, null);
        }
        loggedIn = true;

        ftp.setFileType(fileType);
        ftp.enterLocalPassiveMode();
        OutputStream output = null;
        try {
            output = new FileOutputStream(local);
            LOGGER.info("About to download " + remote + " from " + server
                    + " on " + (port > 0 ? port : ftp.getDefaultPort())
                    + " to " + local);              
            ftp.setControlKeepAliveTimeout(300);
            boolean isFileDownloaded = false;
            try{
                isFileDownloaded = ftp.retrieveFile(remote, output);

            }
            catch(IOException ex){
                if(ftp.isConnected()){

                    try{
                        int retryCode = 0;
                        while (!String.valueOf(retryCode).startsWith("2") && (new Date().getTime() < (startTime_ms + TOTAL_DURATION_MSECS))){
                            try{

                                 retryCode = ftp.retr(local);
                            }catch(Exception e1){
                                Thread.sleep(1000);
                                System.out.println("File not downloaded !! " + e1.toString());
                                ftpConnect(server, ftp, port, startTime_ms);
                            }

                        }
                    }catch(Exception e){
                        //ftp.getReplyCode()
                        //throw e;
                        //disconnect(ftp);
                        //ftpConnect(server, ftp, port, startTime_ms);

                        System.out.println("File not downloaded !! " + e.toString());
                    }                   
                }
            }
            if(isFileDownloaded){
                LOGGER.info("Finished downloading " + remote + " from "
                        + server + " on "
                        + (port > 0 ? port : ftp.getDefaultPort()) + " to "
                        + local);
            }
            else{
                System.out.println("File not downloaded !! ");
            }           

        }catch(IOException io){
            io.printStackTrace();

            throw io;
        }           
        finally {
            if (output != null) {
                try {
                    output.close();
                } catch (IOException f) {
                    LOGGER.severe("output.close() error: "
                            + ServiceUtils.stackToString(f));
                }
            }
        }
    }       
    catch (FTPConnectionClosedException e) {
        LOGGER.severe("Server closed connection: " + server + " "
                + ServiceUtils.stackToString(e));
        throw e;
    } catch (IOException e) {
        LOGGER.severe("IOException, server: " + server + " "
                + ServiceUtils.stackToString(e));
        throw e;
    } finally {
        if (loggedIn) {
            try {
                ftp.logout();
            } catch (IOException f) {
                LOGGER.severe("ftp.logout() error: "
                        + ServiceUtils.stackToString(f));
            }
        }
        disconnect(ftp);
    }
}

我的问题基本上是，如果retrieveFile()方法失败，我是否可以重新连接并从断开连接的位置开始下载。

现在我使用 Microsoft IIS 服务器作为我的 FTP 服务器，但在生产环境中它将是 FileZilla FTP 服务器。

感谢任何帮助。谢谢

Answer 1

很抱歉回复得太晚了。这是我为解决问题所做的:

1. 设置 FileZilla 服务器
2. 使用retrieveFileStream而不是retrieveFile。

3. 保留写入的字节数并使用相同的输出流进行写入。

       BufferedInputStream inputStream = null;
       BufferedOutputStream outputStream = null;
       InputStream in = null;
       int osCount = 0;
       in = ftp.retrieveFileStream(remote);
               inputStream = new BufferedInputStream(in);
               File localFile = new File(local, fileName);
               outputStream = new BufferedOutputStream(new FileOutputStream(localFile));
               for (int read = inputStream.read(); read != -1; read = inputStream.read()) {
                   outputStream.write(read);
                   osCount++;
               }           
               outputStream.flush();
               if (osCount < fileSize) {                       
                   System.out.println(fileName + ": Errored out !!!");
                   BufferedInputStream inputStream1 = null;
                   InputStream in1 = null;
                   if (ftp.isConnected()) {
                       try {
                           while (osCount < fileSize && new Date().getTime() < (startTime_ms + TOTAL_DURATION_MSECS)) {
                               try {                                       
                                       disconnect(ftp);
                                       ftpConnect(server, ftp, port, startTime_ms);
                                       ftp.login(username, password);
                                       ftp.setRestartOffset(osCount);                                      
                                       System.out.println(fileName + ": Re reading from position " + osCount);
                                       in1 = ftp.retrieveFileStream(remote);
                                       inputStream1 = new BufferedInputStream(in1);
                                       for (int read = inputStream1.read(); read != -1; read = inputStream1.read()) {
                                           outputStream.write(read);
                                           osCount++;
                                       }
                                       outputStream.flush();
                                       if(FTPReply.isPositiveCompletion(ftp.getReplyCode())){
                                           isErrored = true;
                                           break;
                                       }
                               } catch (Exception e1) {
                                   Thread.sleep(1000);
                                   LOGGER.severe(fileName + ": File not downloaded " + server + " " + ServiceUtils.stackToString(e1));
                               }
                           }
   
                       } catch (Exception e) {
                           LOGGER.severe(fileName + ": File not downloaded " + server + " " + ServiceUtils.stackToString(e));
                       }
                   }
               }