Question

我使用以下库...

org.apache.commons.net.telnet.TelnetClient;

我有这段代码用于连接服务器。

import org.apache.commons.net.*;
import org.apache.commons.net.ProtocolCommandListener
import org.apache.commons.net.ftp.FTPSClient
import org.apache.commons.net.telnet.TelnetClient;


String server = "some server";
String result = '';

//Create the telnet client and connect on port 43
TelnetClient telnetClient = new TelnetClient();
telnetClient.addProtocolCommandListener(new PrintCommandListener(new PrintWriter(System.out)));
telnetClient.connect(server, 43);

当我到达....

telnetClient.addProtocolCommandListener(new PrintCommandListener(new PrintWriter(System.out)));

我得到以下异常....

抓住：java.lang.NullPointerException 断开与目标VM的连接，地址：＆＃39; 127.0.0.1：3140＆＃39;，transport：＆＃39; socket＆＃39; 显示java.lang.NullPointerException 在org.apache.commons.net.SocketClient.addProtocolCommandListener（SocketClient.java:772）在org.apache.commons.net.SocketClient $ addProtocolCommandListener.call（未知来源）

有人知道为什么我会得到这个例外吗？如果我删除了该行，那么异常就是这一行。如果我使用FTPS客户端，我在同一个库中没有SFTP这个问题！

嗨，感谢您的回复，这是图书馆中一些支持的客户端的简单示例，我猜测whois和ftp客户端可能不支持列表器！？

   import org.apache.commons.net.*;
   import org.apache.commons.net.ProtocolCommandListener;
   import org.apache.commons.net.ftp.FTPClient;
   import org.apache.commons.net.telnet.TelnetClient;
   import org.apache.commons.net.whois.WhoisClient;
   import java.io.PrintWriter;

   public class WhoisExample
   {
       public static void main(String args[])
       {
           try {
               WhoisClient whoisClient = new WhoisClient();
               whoisClient.addProtocolCommandListener(new PrintCommandListener(new PrintWriter(System.out)));
           }
           catch(Exception e) {
               System.out.println("whois client exception" + e);
           }

           try {
               TelnetClient telnetClient = new TelnetClient();
               telnetClient.addProtocolCommandListener(new PrintCommandListener(new PrintWriter(System.out)));
           }
           catch(Exception e) {
               System.out.println("telnet client exception" + e);
           }

           try {
               FTPClient ftpClient = new FTPClient();
               ftpClient.addProtocolCommandListener(new PrintCommandListener(new PrintWriter(System.out)));

               System.out.println("no ftp client exception here !");
           }
           catch(Exception e)
           {
               System.out.println("ftp client exception" + e);
           }
       }
   }

Answer 1

我记录了Apache commons net的一个错误，它已被解决为没问题。

基本上......有些客户目前不支持ProtocolCommand Listener。＆＃39;

您可以从以下链接中找到更多信息....

https://issues.apache.org/jira/browse/NET-608

将addProtocolCommandListener与库org.apache.commons.net.telnet.TelnetClient一起使用时出现未知来源异常

1 个答案: