套接字编程中“ helloworld”服务器和客户端程序中的异常

Question

I am getting this error when I'm running my client program. I was unable to recognise the problem yet.I've changed the port numbers but there is no use. I saw the previous posts regarding the same error but I didn't figured it out.

Server.java

import java.io.*;
import java.net.*;
class Server{

 public static void main(String argv[]) throws Exception 
 {

   String clientSentence;
   String capitalizedSentence;
   ServerSocket welcomeSocket = new ServerSocket(8080);

   while (true) 
   {
      Socket connectionSocket = welcomeSocket.accept();
       BufferedReader inFromClient = new BufferedReader(new 
      InputStreamReader(connectionSocket.getInputStream()));
       DataOutputStream outToClient = new 
       DataOutputStream(connectionSocket.getOutputStream());
       clientSentence = inFromClient.readLine();
        System.out.println("Received: " + clientSentence);
        capitalizedSentence = clientSentence.toUpperCase() + '\n';
         outToClient.writeBytes(capitalizedSentence);
     }
  }
  }

Client.java

import java.io.*;
import java.net.*;

class Client
{
 public static void main(String argv[]) throws Exception 
 {
      String sentence;
      String modifiedSentence;
      BufferedReader inFromUser = new BufferedReader(new InputStreamReader(System.in));
      Socket clientSocket = new Socket("localhost", 8080);    
      DataOutputStream outToServer = new DataOutputStream(clientSocket.getOutputStream());
      BufferedReader inFromServer = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
      sentence = inFromUser.readLine();
      outToServer.writeBytes(sentence + '\n');
      modifiedSentence = inFromServer.readLine();
      System.out.println("FROM SERVER: " + modifiedSentence);
      clientSocket.close();
 }
 }

I am getting an error when I run the client.java

Exception in thread "main" java.net.ConnectException: Connection refused: connect
at java.net.DualStackPlainSocketImpl.connect0(Native Method)
at java.net.DualStackPlainSocketImpl.socketConnect(Unknown Source)
at java.net.AbstractPlainSocketImpl.doConnect(Unknown Source)
at java.net.AbstractPlainSocketImpl.connectToAddress(Unknown Source)
at java.net.AbstractPlainSocketImpl.connect(Unknown Source)
at java.net.PlainSocketImpl.connect(Unknown Source)
at java.net.SocksSocketImpl.connect(Unknown Source)
at java.net.Socket.connect(Unknown Source)
at java.net.Socket.connect(Unknown Source)
at java.net.Socket.<init>(Unknown Source)
at java.net.Socket.<init>(Unknown Source)
at Client.main(Client.java:11)

Can anyone help with this error?

Answer 1

The Client and Server Program runs perfectly fine for me.

1. Can you check if there is some process already listening on that port.