Java到FileZilla FTP客戶端：套接字寫入錯誤

Question

這些天，另一個挑戰使我頭痛不已。我正在嘗試在Java中創建一個應該能夠與FileZilla FTP客戶端進行通信的FTP服務器。代碼不是最好的，因爲我嘗試了很多事情來了解發生了什麼。

這裏的FileZilla記錄來自德國

Status: Connect to 127.0.0.1:21... 
Status: Connected!Waiting for welcome message. 
Response: 220 localhost connected 
Error: Establishing connection to server failed. 

主要問題到目前爲止轉化是建立真正的聯繫。套接字已連接，我可以向客戶端發送至少一條消息，但沒有機會獲得客戶端輸入，例如用於PASV，USER和PASS。

import java.awt.BorderLayout; 
import java.awt.Container; 
import java.awt.event.ActionEvent; 
import java.awt.event.ActionListener; 
import java.awt.event.WindowEvent; 
import java.awt.event.WindowListener; 
import java.io.DataInputStream; 
import java.io.DataOutputStream; 
import java.io.IOException; 
import java.io.InputStream; 
import java.io.OutputStream; 
import java.net.ServerSocket; 
import java.net.Socket; 
import java.net.SocketException; 

import javax.swing.JButton; 
import javax.swing.JFrame; 

public class FTP_Server extends JFrame implements ActionListener, WindowListener { 
    private static final long serialVersionUID = 1L; 

    private Container cp; 
    private JButton btncon; 
    private ServerSocket listenSocket; 
    private Socket connectionSocket; 
    private DataOutputStream dos; 
    private DataInputStream dis; 
    private OutputStream os; 
    private InputStream is; 

    public FTP_Server() { 
     super("FTP Server"); 

     this.setDefaultCloseOperation(EXIT_ON_CLOSE); 

     cp = this.getContentPane(); 
     cp.setLayout(new BorderLayout()); 

     btncon = new JButton("Connect"); 
     btncon.addActionListener(this); 

     cp.add(btncon, BorderLayout.CENTER); 

     this.pack(); 
     this.setVisible(true); 
    } 

    @Override 
    public void actionPerformed(ActionEvent e) { 
     if(e.getSource().equals(btncon)){ 
      createConnection(); 
     } 
    } 

    public void createConnection() { 
     System.out.println("Connecting..."); 
     try { 
      listenSocket = new ServerSocket(21); 
      listenSocket.setSoTimeout(0); 
      connectionSocket = listenSocket.accept(); 
      connectionSocket.setSoLinger(true, 0); 
      connectionSocket.setSoTimeout(0); 
      connectionSocket.setKeepAlive(true); 
      System.out.println("Connected!"); 

      os = connectionSocket.getOutputStream(); 
      dos = new DataOutputStream(os); 

      is = connectionSocket.getInputStream(); 
      dis = new DataInputStream(is); 

      while(connectionSocket.isConnected() == true) { 
       dos.writeUTF("220 localhost connected\r\n"); 
       //Will cause socket write error soon! 
       dos.flush(); 
       dos.writeUTF("331 Anonym no password needed\r\n"); 
       System.out.println(is.read()); 
      } 
     } catch (SocketException exp) { 
      try { 
       listenSocket.close(); 
       System.out.println("Disconnected"); 
       exp.printStackTrace(); 
      } catch (IOException exp2) { 
       exp2.printStackTrace(); 
      } 
     } catch (IOException exp) { 
      exp.printStackTrace(); 
     } 
    } 

    @Override 
    public void windowOpened(WindowEvent e) { 
     // TODO Auto-generated method stub 

    } 

    @Override 
    public void windowClosing(WindowEvent e) { 
     System.exit(0); 
    } 

    @Override 
    public void windowClosed(WindowEvent e) { 
     // TODO Auto-generated method stub 

    } 

    @Override 
    public void windowIconified(WindowEvent e) { 
     // TODO Auto-generated method stub 

    } 

    @Override 
    public void windowDeiconified(WindowEvent e) { 
     // TODO Auto-generated method stub 

    } 

    @Override 
    public void windowActivated(WindowEvent e) { 
     // TODO Auto-generated method stub 

    } 

    @Override 
    public void windowDeactivated(WindowEvent e) { 
     // TODO Auto-generated method stub 

    } 
} 

對於錯誤消息/打印堆棧：

java.net.SocketException: Software caused connection abort: socket write error 
    at java.net.SocketOutputStream.socketWrite0(Native Method) 
    at java.net.SocketOutputStream.socketWrite(SocketOutputStream.java:109) 
    at java.net.SocketOutputStream.write(SocketOutputStream.java:153) 
    at java.io.DataOutputStream.write(DataOutputStream.java:107) 
    at java.io.DataOutputStream.writeUTF(DataOutputStream.java:401) 
    at java.io.DataOutputStream.writeUTF(DataOutputStream.java:323) 
    at ftp.FTP_Server.createConnection(FTP_Server.java:82) 
    at ftp.FTP_Server.actionPerformed(FTP_Server.java:58) 
    at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2018) 
    at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2341) 
    at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402) 
    at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259) 
    at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:252) 
    at java.awt.Component.processMouseEvent(Component.java:6505) 
    at javax.swing.JComponent.processMouseEvent(JComponent.java:3321) 
    at java.awt.Component.processEvent(Component.java:6270) 
    at java.awt.Container.processEvent(Container.java:2229) 
    at java.awt.Component.dispatchEventImpl(Component.java:4861) 
    at java.awt.Container.dispatchEventImpl(Container.java:2287) 
    at java.awt.Component.dispatchEvent(Component.java:4687) 
    at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4832) 
    at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4492) 
    at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4422) 
    at java.awt.Container.dispatchEventImpl(Container.java:2273) 
    at java.awt.Window.dispatchEventImpl(Window.java:2719) 
    at java.awt.Component.dispatchEvent(Component.java:4687) 
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:723) 
    at java.awt.EventQueue.access$200(EventQueue.java:103) 
    at java.awt.EventQueue$3.run(EventQueue.java:682) 
    at java.awt.EventQueue$3.run(EventQueue.java:680) 
    at java.security.AccessController.doPrivileged(Native Method) 
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76) 
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:87) 
    at java.awt.EventQueue$4.run(EventQueue.java:696) 
    at java.awt.EventQueue$4.run(EventQueue.java:694) 
    at java.security.AccessController.doPrivileged(Native Method) 
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76) 
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:693) 
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:244) 
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:163) 
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:151) 
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:147) 
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:139) 
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:97) 

Answer 1

我仍然遇到消息傳遞的問題。我現在做的是爲每個連接的套接字以及現在的每個輸出流創建一個新的線程。

package ftp; 

import java.io.DataOutputStream; 
import java.io.IOException; 

public class MultiIO implements Runnable{ 
    private DataOutputStream dos; 

    public MultiIO(DataOutputStream stream) { 
     dos = stream; 
     System.out.println("Set OutputStream."); 
    } 

    @Override 
    public void run() { 
     try { 
      dos.writeBytes("220"); 
      dos.flush(); 
      System.out.println("tried once"); 
     } catch (IOException e) { 
      System.exit(-1); 
     } 
    } 
} 

現在的問題是FileZilla客戶端不會得到220消息。

這裏是新的套接字處理類。我有點從甲骨文網頁複製它。

package ftp; 

import java.io.DataOutputStream; 
import java.io.IOException; 
import java.io.OutputStream; 
import java.net.Socket; 
import java.net.SocketException; 

public class MultiConnection implements Runnable{ 
    private Socket cSocket; 

    public MultiConnection(Socket client) { 
     cSocket = client; 
     System.out.println("Connected!"); 
    } 

    @Override 
    public void run() { 
     OutputStream os = null; 
     DataOutputStream dos = null; 
     try { 
      os = cSocket.getOutputStream(); 
      dos = new DataOutputStream(os); 
     } catch (SocketException es) { 
      es.printStackTrace(); 
     } catch (IOException e) { 
      System.exit(-1); 
     } 

     MultiIO mio; 
     mio = new MultiIO(dos); 
     Thread thio = new Thread(mio); 
     thio.start(); 
    } 
} 

Answer 2

許多錯誤這裏。

1. 不要亂用SO_LINGER。這是沒有必要的，它只會導致更多的不必要的痛苦。
2. writeUTF（）寫入只讀readUTF（）可以讀取的格式。這不是與非Java客戶端進行通信的一種方式。
3. 您不是在單獨的線程中處理接受的套接字，因此您一次只能處理一個客戶端。
4. isConnected（）不是連接狀態的有效測試。它會告訴你你是否連接過這個插座。你做到了，所以它會迴歸真實。當對方斷開連接時，這不會改變。您需要以通常的方式測試EOS，並在各種讀取API中進行記錄。
5. 當您在接受的套接字上發生IOException時，不需要關閉偵聽套接字。
6. 我不明白爲什麼一個FTP服務器需要一個GUI，但是如果這樣做，它必須執行所有的網絡I/O，包括接受連接，在一個單獨的線程從AWT線程。
7. 您只需要告訴客戶端他已成功連接一次，而不是無限次數。

這就足夠了。