java - ftpClient.retrieveFileStream(filepath) 返回 null

Question

我有一个文件夹，它在 ftp 中有 3 个文件。对于第一个文件，bufferreader 正在成功读取。但是从第二个文件 InputStream 获取为 null。不知道是什么原因。

我的代码是

import java.io.BufferedReader;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
 import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.SocketException;
import java.util.logging.Logger;

import org.apache.commons.net.ftp.FTPClient;
import org.apache.commons.net.ftp.FTPFile;
import org.apache.commons.net.ftp.FTPReply;

public class ExtractFile{

 public static void main(String args[]) {

 // get an ftpClient object
 FTPClient ftpClient = new FTPClient();
 FileOutputStream fos = null;

  try {
  // pass directory path on server to connect
  ftpClient.connect("XXXX");

  // pass username and password, returned true if authentication is
 // successful
  boolean login = ftpClient.login("XXXX", "XXXXX");

 if (login) {
System.out.println("Connection established...");

FTPFile[] files=ftpClient.listDirectories();
for(int i=0;i<files.length;i++){


    FTPFile file=files[i];

    BufferedReader reader = null;
    String firstLine = null;

    try {

        String currentline=null;

        listDirectory(ftpClient, ftpClient.printWorkingDirectory(), "", 0);


    } finally {
        if (reader != null) try { reader.close(); } catch (IOException logOrIgnore) {}
    }



}


   boolean logout = ftpClient.logout();
   if (logout) {
    System.out.println("Connection close...");
    }
   } else {
   System.out.println("Connection fail...");
  }

  } catch (SocketException e) {
   e.printStackTrace();
  } catch (IOException e) {
  e.printStackTrace();
  } finally {
   try {
  ftpClient.disconnect();
  } catch (IOException e) {
  e.printStackTrace();
 }
}
}
 static void listDirectory(FTPClient ftpClient, String parentDir,
        String currentDir, int level) throws IOException {
    String dirToList = parentDir;
    if (!currentDir.equals("")) {
        dirToList += "/" + currentDir;
    }

    FTPFile[] subFiles = ftpClient.listFiles(dirToList);

    if (subFiles != null && subFiles.length > 0) {
        for (FTPFile aFile : subFiles) {
            String currentFileName = aFile.getName();

            if (currentFileName.equals(".")
                    || currentFileName.equals("..")) {

                continue;
            }
            for (int i = 0; i < level; i++) {
                System.out.print("\t");
            }
            if (aFile.isDirectory()) {
                System.out.println("[" + currentFileName + "]");
                listDirectory(ftpClient, dirToList, currentFileName, level + 1);
            } else {
                System.out.println(currentFileName);
                String currentline=null;
                BufferedReader reader = null;
                String firstLine = null;

                /*****here i am getting stream as null**********/
                InputStream stream = ftpClient.retrieveFileStream(dirToList+"/"+currentFileName);                   



                reader = new BufferedReader(new InputStreamReader(stream, "UTF-8"));
                String[] lines=new String[5];
                int i=0;

                    //TODO 

                while((currentline=reader.readLine())!=null){
                    lines[i]=currentline;
                    i++;
                        System.out.println(".."+currentline);
                }

             }

        }
    }
  }
 }

为什么我从第二个文件中得到的 InputStream 为空？？

Answer 1

我遇到了同样的问题，通过调用 completePendingCommand() 并验证传输确实成功解决了这个问题，从而完成了文件传输。

如 documentation 中所述

To finalize the file transfer you must call completePendingCommand and check its return value to verify success. If this is not done, subsequent commands may behave unexpectedly.

如果这不能解决问题，请使用 getReplyCode() 或 getReplyString() 或 getReplyStrings() 查看确切的问题是什么。

编辑:刚注意到这是一篇很旧的帖子。但希望它会对其他人有所帮助。