Exception in "helloworld" server and client program in socket programming

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?

When it's a question you use a question mark not three exclamation marks — L_Church
– L_Church, Commented Apr 11, 2018 at 11:52

piy26 · Accepted Answer · 2018-04-11 11:58:21Z

1

The Client and Server Program runs perfectly fine for me.

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

answered Apr 11, 2018 at 11:58

piy26

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8 Comments

Rainer Over a year ago

Was about to say the same. Copy&Past --> Works just fine. Under Windows you can use the "netstat" cmd line tool to check if the port is used. With "-b" it will even tell you which application (requires admin privileges)

Lahari Over a year ago

No, I've checked

Lahari Over a year ago

I am getting "The requested operation requires elevation." when I am using <netstat -b> @Rainer

piy26 Over a year ago

Can you check again if your server program is indeed running. I guess server program is not even starting in your case. When i terminated my server program and then ran the client, I got the same stack as yours.

Lahari Over a year ago

When I run my server program there is no response it is running still... @piy26

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