java套接字编程问题

Question

客户端:

  import java.io.*;
  import java.net.*;
  public class Requester
  {
        Socket requestSocket;
        ObjectOutputStream out;
        ObjectInputStream in;
        String message;
        BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
        Requester(){}
        void run() throws IOException
        {
            try{
                //1. creating a socket to connect to the server
                requestSocket = new Socket("172.16.3.219", 2004);
                System.out.println("Connected to localhost in port 2004");

                //2. get Input and Output streams
                out = new ObjectOutputStream(requestSocket.getOutputStream());
                out.flush();
                in = new ObjectInputStream(requestSocket.getInputStream());

                //3: Communicating with the server
                do{
                     try{
                        message = (String)in.readObject();
                        System.out.println("server>" + message);
                        message=br.readLine();
                        sendMessage(message);
                     }
                        catch(ClassNotFoundException classNot)
                        {
                           System.err.println("data received in unknown format");
                    }
                }while(!message.equals("bye"));
               }
               catch(UnknownHostException unknownHost)
               {
                System.err.println("You are trying to connect to an unknown host!");
               }
               catch(IOException ioException)
               {
                ioException.printStackTrace();
               }
               finally
               {
                //4: Closing connection
                try{
                    in.close();
                    out.close();
                    requestSocket.close();
                   }
                  catch(IOException ioException)
                  {
                    ioException.printStackTrace();
                  }
               }
        }
        void sendMessage(String msg)
        {
            try{
                out.writeObject(msg);
                out.flush();
                System.out.println("client1>" + msg);
               }
              catch(IOException ioException)
              {
                ioException.printStackTrace();
              }
        }
        public static void main(String args[]) throws IOException
        {
            Requester client = new Requester();
            client.run();
        }
    }

服务器:

import java.io.*;
import java.net.*;
public class Provider
{
    ServerSocket providerSocket;
    Socket connection = null;
    ObjectOutputStream out;
    ObjectInputStream in;
    String message;
    Provider(){}
    BufferedReader br=new BufferedReader(new InputStreamReader(System.in));

    void run()
    {
        try{
            //1. creating a server socket
            providerSocket = new ServerSocket(2004, 10);

            //2. Wait for connection
            System.out.println("Waiting for connection");

              connection = providerSocket.accept();
              System.out.println("Connection received from" + connection.getInetAddress().getHostName());

            //3. get Input and Output streams
                out = new ObjectOutputStream(connection.getOutputStream());
            out.flush();
            in = new ObjectInputStream(connection.getInputStream());
            sendMessage("Connection successful");

            //4. The two parts communicate via the input and output streams
            do
            {
               try
               {
                    message = (String)in.readObject();
                    System.out.println("client>" + message);

                    if (message.equals("bye"))
                    {
                        sendMessage("bye");
                    }
                        else
                    {
                        message=br.readLine();
                        sendMessage(message);
                    }
              }
              catch(ClassNotFoundException classnot)
              {
                System.err.println("Data received in unknown format");
              }
            }while(!message.equals("bye"));
        }
        catch(IOException ioException)
        {
            ioException.printStackTrace();
        }
        finally
        {
            //4: Closing connection
            try{
                        in.close();
                        out.close();
                        providerSocket.close();
               }
              catch(IOException ioException)
              {
                            ioException.printStackTrace();
              }
            }
    }

        void sendMessage(String msg)
    {
        try
        {
            out.writeObject(msg);
            out.flush();
            System.out.println("server>" + msg);
        }
        catch(IOException ioException)
        {
            ioException.printStackTrace();
        }
    }
    public static void main(String args[])throws IOException
    {
       Provider server = new Provider();
       while(true)
       {
        server.run();
       }
    }
}                                                                                                                                                                                                               

服务器程序位于172.16.3.219。如果服务器和客户端都在一个系统(172.16.3.219)中，程序正在工作。如果将我的客户端程序放在其他系统中，让我们说172.16.3.30，我会收到异常(服务器仍然位于172.16.3.219)。我应该更改 socket() 构造函数吗？如果问题出在构造函数上，当客户端和服务器位于不同系统时，建议我使用合适的构造函数

Answer 1

代码看起来不错；您的客户端或服务器上有防火墙吗？

我试图测试发送邮件的代码。为此，我安装了本地邮件服务器，但无法连接:管理员已禁用 SMTP 端口以阻止垃圾邮件发送者。

[编辑]“连接被拒绝”意味着没有服务器在该服务器上的该端口上运行。运行 netstat -tan (Linux) 或 netstat -tn (Windows) 并查找带有 LISTEN 的行。这些是正在运行的服务器进程。输出将如下所示:

 Active Internet connections (servers and established)
 Proto Recv-Q Send-Q Local Address           Foreign Address         State      
 tcp        0      0 0.0.0.0:8080            0.0.0.0:*               LISTEN     
 tcp        0      0 127.0.0.1:631           0.0.0.0:*               LISTEN     

有趣的部分是“本地地址”。它包含服务器正在监听的网络接口(interface)(IP 地址)。第一个条目监听所有网络接口(interface)，而第二个条目附加到“localhost”(也称为“本地环回”)。它将忽略来自 LAN 的任何连接尝试。

确保您的服务器以 0.0.0.0:2004 列出。如果不是，请尝试:

 providerSocket = ServerSocket(2004, 10, InetAddress.getByName("0.0.0.0"));

如果不起作用，请尝试服务器网卡的公共(public)IP地址。