Communication deadlock in single server and multiple clients

Question

I am beginner in Java and programming a chat-server application. The application facilitates chat among n number of clients

Current Problem
In my code below the Chatinterface classis the client class. After I open my 2 instances of Chatinterfaceclass, when I try to communicate by entering a message in the text area. I do not receive the message in the another client instance window and vice versa. Either my socket is not communicating or there is some other problem.

Expected Output

Both the clients must communicate and the messages must be displayed in the respective window.

Could any one tell me what's going on wrong and where can I correct my code ?

Anyways I am pasting both my client and server code for a detailed analysis.

package stack;

import java.awt.EventQueue;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.Insets;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.Socket;
import java.net.UnknownHostException;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JPasswordField;
import javax.swing.JTextArea;
import javax.swing.JTextField;
import javax.swing.SpringLayout;
import javax.swing.SwingUtilities;
import javax.swing.WindowConstants;
class Chatinterface implements ActionListener {
    private JFrame frame;
    JTextArea textArea_1;
    JTextArea textArea_2;
    JButton btnNewButton;
    JButton btnNewButton_1;
    Socket client;
    BufferedReader read;
    PrintWriter write;
    String getmsg;
    String gettext;
    public Chatinterface(){
        communicate();
        displaygui();
    }
    private void communicate() {
        // TODO Auto-generated method stub
        try {
            client = new Socket("localhost",3420);
            read = new BufferedReader(new InputStreamReader(client.getInputStream()));
            write = new PrintWriter(client.getOutputStream(),true);
            if(getmsg!=null)
            {
                while(true)
                {
                    textArea_2.setText(getmsg);
                }
            }

        } catch (UnknownHostException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

    private void displaygui() {
        frame = new JFrame();
        frame.setResizable(false);
        frame.setBounds(100, 100, 450, 300);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        SpringLayout springLayout = new SpringLayout();
        frame.getContentPane().setLayout(springLayout);
        textArea_1 = new JTextArea();
        springLayout.putConstraint(SpringLayout.NORTH, textArea_1, 171, SpringLayout.NORTH, frame.getContentPane());
        springLayout.putConstraint(SpringLayout.WEST, textArea_1, 10, SpringLayout.WEST, frame.getContentPane());
        springLayout.putConstraint(SpringLayout.SOUTH, textArea_1, -10, SpringLayout.SOUTH, frame.getContentPane());
        springLayout.putConstraint(SpringLayout.EAST, textArea_1, 340, SpringLayout.WEST, frame.getContentPane());
        frame.getContentPane().add(textArea_1);
        textArea_2 = new JTextArea();
        textArea_2.setWrapStyleWord(true);
        textArea_2.setEditable(false);
        springLayout.putConstraint(SpringLayout.NORTH, textArea_2, 10, SpringLayout.NORTH, frame.getContentPane());
        springLayout.putConstraint(SpringLayout.WEST, textArea_2, 0, SpringLayout.WEST, textArea_1);
        springLayout.putConstraint(SpringLayout.SOUTH, textArea_2, 160, SpringLayout.NORTH, frame.getContentPane());
        springLayout.putConstraint(SpringLayout.EAST, textArea_2, 0, SpringLayout.EAST, textArea_1);
        frame.getContentPane().add(textArea_2);
        btnNewButton = new JButton("Send");
        springLayout.putConstraint(SpringLayout.NORTH, btnNewButton, -76, SpringLayout.SOUTH, frame.getContentPane());
        springLayout.putConstraint(SpringLayout.WEST, btnNewButton, 5, SpringLayout.EAST, textArea_1);
        springLayout.putConstraint(SpringLayout.SOUTH, btnNewButton, -27, SpringLayout.SOUTH, frame.getContentPane());
        springLayout.putConstraint(SpringLayout.EAST, btnNewButton, 82, SpringLayout.EAST, textArea_1);
        frame.getContentPane().add(btnNewButton);
        btnNewButton.addActionListener(this);
        btnNewButton.setActionCommand("S");
        btnNewButton_1 = new JButton("Logout");
        springLayout.putConstraint(SpringLayout.NORTH, btnNewButton_1, 50, SpringLayout.NORTH, frame.getContentPane());
        springLayout.putConstraint(SpringLayout.WEST, btnNewButton_1, -65, SpringLayout.EAST, btnNewButton);
        springLayout.putConstraint(SpringLayout.SOUTH, btnNewButton_1, 108, SpringLayout.NORTH, frame.getContentPane());
        springLayout.putConstraint(SpringLayout.EAST, btnNewButton_1, 0, SpringLayout.EAST, btnNewButton);
        frame.getContentPane().add(btnNewButton_1);
        btnNewButton_1.addActionListener(this);
        btnNewButton_1.setActionCommand("L");
        frame.setVisible(true);
    }
    public static void main(String args[])
    {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                try {
                    new Chatinterface();
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }

    @Override
    public void actionPerformed(ActionEvent arg0) {

        if(arg0.getActionCommand().equals("S"))
        {   
            String gettext2;
            gettext2 = textArea_1.getText();
            textArea_2.append(gettext2);
            textArea_1.setText("");
            write.println(gettext2);
        }

        if(arg0.getActionCommand().equals("L")){
            try {
                read.close();
                write.close();
                client.close();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
    }
}

Here is the code for the server class

package stack;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.*;
public class Server1  {
    public static void main(String[] args) throws Exception {
        Socket s;
        ServerSocket server = new ServerSocket(3420);
        while(true)
        {
            s = server.accept();
            Handler handler1 = new Handler(s);
            Thread t1 = new Thread(handler1);
            t1.start();


        }
    }
}

Here is the handler class

package stack;

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

public class Handler implements Runnable {

    Socket s;

    String getmsg = null;
    String sendmsg;

    public Handler(Socket s) {
        this.s = s;

    }

    public void run() {

        try {
            BufferedReader reader1;
            PrintWriter writer1;
            reader1 = new BufferedReader(new InputStreamReader(
                    s.getInputStream()));
            writer1 = new PrintWriter(s.getOutputStream(), true);
            sendmsg = reader1.readLine();

            while (true) {
                if (reader1 == null) {

                    s.close();
                } else {
                    writer1.println(sendmsg);
                }
            }

        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

    }

}

score 2 · Answer 1 · edited May 23 '17 at 10:26

2

Your code is complex to read and understand. Try to use relevant variable names. Try to focus on code relevant to the question.

I don't know what your problem is, but I'm sure there is something wrong here :

e.getActionCommand() == "s"

and here

if (e.getActionCommand() == "L")

None of those will be true (it test for pointer equality, not content) (read more here).

So write this :

e.getActionCommand().equals("s")

and

if (e.getActionCommand().equals("L"))

For any further problem :

use debugger
use logs

edited May 23 '17 at 10:26

Community

1
1

answered Aug 02 '14 at 10:32

ben75

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I have edited my question and provided a clear description above. I have also simplified the code. – Memory bot Aug 02 '14 at 15:14

score 0 · Answer 2 · answered Aug 03 '14 at 02:04

As said by ben75 the code is very difficult to read and has some errors. Let me provide some suggestions to be able to help you:

1-Do not create functionality within the constructor. This is what you do in Chatinterface. The constructor should only create the object. Then you can add a method called "execute" to do the work.

private void execute()
{
    ...
}

2-I haven't tested the communication part but it should communicate alright between client and server. I run Chatinterface and the code reaches correctly this line:

write.println(gettext2);

3-The error why you don't see the message is because, in the constructor, it is calling communicate and the displaygui. The code in communicate is the one that should display the message received back form server:

        if(getmsg!=null)
        {
            while(true)
            {
                textArea_2.setText(getmsg);
            }
        }

But this code is executed only once at the beginning, getmsg is null, and execution control never comes back again to this code. I assume you are trying to create a different thread in the client that is going to execute this code and enter the infinite loop.

If you doubt about the communication client-server you can use Wireshark or tcpdump to sniff the communication.

There is not deadlock here.

Communication deadlock in single server and multiple clients

2 Answers2