为什么我的 FTP 客户端无法连接到服务器？

Question

我创建了一个无法连接到服务器的 FTP 客户端（被动）。我使用的 FTP 服务器是 Filezilla；我只是用它来测试。每次我运行 java 程序（FTP 客户端）时，Filezilla 都会断开连接，并且在 Eclipse 中出现这些错误：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);
        //}
 }

}

这是我连接的程序：

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");

    }

}

我也试过写我的局域网ip而不是"localhost"

Answer 1

... 220-FileZilla 服务器版本 0.9.50 beta

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

您期望以220<space> 开头的响应，而服务器向您发送以220- 开头的响应。请阅读standard 了解如何处理多行回复。