为什么套接字连接到端口 23 不起作用？

发布于 2024-07-29 06:05:07 字数 942 浏览 4 评论 0原文

我有这个小的测试套接字连接类：-

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

public class TestTelnet {

public static void main(String args[]) throws Exception {
    Telnet telnet = new Telnet(); 
    Socket socket = null ;
    socket = new Socket("localhost", 23);
    socket.setKeepAlive(true);
    BufferedReader r = new BufferedReader(new InputStreamReader(socket.getInputStream()));

        BufferedWriter w = new BufferedWriter(new OutputStreamWriter(socket.getOutputStream()));
    System.out.println(r.readLine());
    socket.close();
}
}

当我使用另一个端口（例如 SMTP 的 25）时它工作得很好，并且 r.readLine 的 println 工作得非常好。我还可以通过命令提示符 (telnet localhost 23) 连接到端口 23，并得到以下返回信息：-

Ubuntu 8.10 my-laptop 登录：

但是当我尝试使用 java 类连接到端口 23 时，它只是挂在 readLine println 上。有人知道为什么吗？

原文

I have this small test socket connection class:-

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

public class TestTelnet {

public static void main(String args[]) throws Exception {
    Telnet telnet = new Telnet(); 
    Socket socket = null ;
    socket = new Socket("localhost", 23);
    socket.setKeepAlive(true);
    BufferedReader r = new BufferedReader(new InputStreamReader(socket.getInputStream()));

        BufferedWriter w = new BufferedWriter(new OutputStreamWriter(socket.getOutputStream()));
    System.out.println(r.readLine());
    socket.close();
}
}

It works perfectly well when I use another port (for example 25 for SMTP) and the println of r.readLine works brilliantly. I can also connect to port 23 via the command prompt (telnet localhost 23) and I get the following returned:-

Ubuntu 8.10
my-laptop login:

But when I try and connect to port 23 using my java class, it just hangs on the readLine println. Does anyone know why this is?

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