为什么我无法将我的FTP客户端连接到服务器？

Question

我制作了一个不能连接到服务器的FTP客户端（被动）。我使用的FTP服务器是Filezilla;我只是用它进行测试。我每次运行Java程序（FTP客户端）FileZilla中断开，我在Eclipse中得到这些错误：Exception in thread "main" java.io.IOException: SimpleFTP received an unknown response when connecting to the FTP server: 220-FileZilla Server version 0.9.50 beta at ftp.ftp.connect(ftp.java:25) at ftp.test.main(test.java:12)

这是FTP客户端：

package ftp; 

import java.io.BufferedReader; 
import java.io.BufferedWriter; 
import java.io.IOException; 
import java.io.InputStreamReader; 
import java.io.OutputStreamWriter; 
import java.net.Socket; 

public class ftp 
{ 

public synchronized void connect(String host, int port, String user, 
      String pass) throws IOException { 
    Socket socket = new Socket(host, port); 
    // if (socket != null) { 
    //  throw new IOException("SimpleFTP is already connected. Disconnect first."); 
    // } 
     // socket = new Socket(host, port); 
     BufferedReader reader = new BufferedReader(new InputStreamReader(socket.getInputStream())); 
     BufferedWriter writer = new BufferedWriter(
      new OutputStreamWriter(socket.getOutputStream())); 

     String response = reader.readLine(); 
     if (!response.startsWith("220-")) { 
      throw new IOException(
       "SimpleFTP received an unknown response when connecting to the FTP server: " 
        + response); 
     } else System.out.println("1:"+response); 

     writer.write("user geek"+"\r\n"); 
     writer.flush(); 
     response= reader.readLine(); 
     System.out.println("2"+response); 
     // response = reader.readLine(); 
     /* if (!response.startsWith("331 ")) { 
      throw new IOException(
       "SimpleFTP received an unknown response after sending the user: " 
        + response); 
     } 
     else {*/ 
     writer.write("PASS hello" +"\r\n"); 
     writer.flush(); 
      response= reader.readLine(); 
      System.out.println("3"+response); 
     //} 


     response = reader.readLine(); 
     /*if (!response.startsWith("230 ")) { 
      throw new IOException(
       "SimpleFTP was unable to log in with the supplied password: " 
        + response); 
     } 
     else {*/ 
      System.out.println("4"+response); 
     //} 
} 

} 

而这正是我连接程序：

package ftp; 

import java.util.Scanner; 

public class test { 
private static Scanner scan; 

public static void main(String args[]) throws Exception 
    { 

     ftp s = new ftp(); 
      s.connect("localhost",21,"geek", "hello"); 

    } 

} 

也试图写我的局域网IP，而不是"localhost"

Answer 1

... 220-的FileZilla Server版本0.9.50 Beta版

if (!response.startsWith("220 ")) { 

你期待与220<space>开始，而服务器发送你开始220-一个响应的响应。请阅读standard以了解如何处理多行回复。