readLine() not working.

[space.puffin]

Hi All.

I'm building a simple Chat client / server. The Client connects to the server and both write to each other, but no output is displayed by each after the readLine() statement. I'm using Threads.

ChatServer.java:

/*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */
package chatserver;

import java.io.BufferedReader;
import java.io.DataInputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.logging.Level;
import java.util.logging.Logger;

/**
 *
 * @author Rob
 */
public class ChatServer implements Runnable {
    int x[] = new int[4];
    int y[] = new int[4];
    BufferedReader reader;
    PrintWriter writer;
    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        ChatServer server = new ChatServer();
        server.run();
        
        
     
    }

    
    public void run() {
        System.out.println("hello");
        connect();
        Thread readerThread = new Thread(new IncomingReader());
        Thread writerThread = new Thread(new OutgoingWriter());
        readerThread.start();
        writerThread.start();
    }
    
    public  void connect() {
          try {
            ServerSocket serverSock = new ServerSocket(4242);
            
            while (true) {
                Socket sock = serverSock.accept();
                writer = new PrintWriter(sock.getOutputStream());
                reader = new BufferedReader(new InputStreamReader(sock.getInputStream()));
                System.out.println("NEtowrking established");
             }
        } catch (IOException ex) {
           ex.printStackTrace();
        }
        
    }

        public class IncomingReader implements Runnable {
            public void run() {
            try {
                String result = reader.readLine();
                reader.close();
                System.out.println("read " + result);
                writer.close();
            } catch (IOException ex) {
                ex.printStackTrace();
            }
            }
        }

        public class OutgoingWriter implements Runnable {
            public void run() {
                
                writer.println("hello");
                System.out.println("Written");
                
                
                }
                              
            }
}

ChatClient.java

/*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */
package chatclient;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.Socket;

/**
 *
 * @author Rob
 */
public class ChatClient {

    BufferedReader reader;
    PrintWriter writer;
    Socket sock;

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        ChatClient client = new ChatClient();
        client.SetUpNetworking();
    }

    private void SetUpNetworking() {
        try {
            sock = new Socket("127.0.0.1", 4242);
            InputStreamReader streamReader = new InputStreamReader(sock.getInputStream());
            reader = new BufferedReader(streamReader);
            writer = new PrintWriter(sock.getOutputStream());
            System.out.println("Netowrking Established");
            Thread readerThread = new Thread(new IncomingReader(reader));
            Thread writerThread = new Thread(new OutgoingWriter(writer));
            readerThread.start();
            writerThread.start();
        } catch (Exception ex) {
            ex.printStackTrace();
        }
    }
    class IncomingReader implements Runnable{
        private BufferedReader reader;
        
        public IncomingReader(BufferedReader reader) {
        this.reader = reader;
    }
        
            public void run() {   
            try {   
                String result = reader.readLine();   
                reader.close();   
                System.out.println("read " + result);   
                   
            } catch (IOException ex) {   
                ex.printStackTrace();   
            }   
        
    }
    }
            public class OutgoingWriter implements Runnable {   
            private PrintWriter writer;

            public OutgoingWriter(PrintWriter writer) {
                this.writer = writer;
            }

            public void run() {   
                writer.println("hello");   
                System.out.println("Written");   
                }   
                                 
            }   
    }

[space.puffin]

Just realised the thread IncomingReader won't execute, if the OutgoingWriter thread is run before the incomingReader thread it won't execute. No idea as to why.

Thanks in advance.

[Norm]

You need to add lots more printlns so you can see where the execution flow goes and where it is getting hung.

[space.puffin]

Odd.

After the try / catch block of connect() System.out.println won't show.

[Norm]

Try flushing the writer after writing.

[space.puffin]

writer.flush() makes no difference. IncomingReader won't execute.

[Norm]

Remove all the close statements.

[space.puffin]

^ tried that already.

[Norm]

Here is what is printed when I execute the code:

CS - Starting
CC- Netowrking Established
CS - Waiting on connnect
CC - IR waiting
CC - writing
CC Written
CS - NetWorking established
CS back from connect
CS - IR waiting
CS read hello from CC<<<<<<<<<<<<<<<<
CS - sending message
CC - read hello from CS>>>>>>>>>>>>>>>
CS Written

0 error(s)

[space.puffin]

Must be an error in my environment. Have tried compiling and running both classes from the commandline. I have the latest version of the jdk installed.

[Norm]

Did you notice these lines in my print out?

CS back from connect
CS - IR waiting


Did you add print statements at those locations in the code?

[space.puffin]

Thanks Norm.

I have println statements after connect in ChatServer.main after connect() .and at the start of IR. neither is printed.

[space.puffin]

ChatServer.java.

/*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */

import java.io.BufferedReader;
import java.io.DataInputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.logging.Level;
import java.util.logging.Logger;

/**
 *
 * @author Rob
 */
public class ChatServer implements Runnable {
    int x[] = new int[4];
    int y[] = new int[4];
    BufferedReader reader;
    PrintWriter writer;
    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        ChatServer server = new ChatServer();
        server.run();
        
        
     
    }

    
    public void run() {
        System.out.println("hello");
        connect();
        System.out.println("going to start thread");
        Thread readerThread = new Thread(new IncomingReader());
        System.out.println("reader started");
        Thread writerThread = new Thread(new OutgoingWriter());
        
        writerThread.start();
        readerThread.start();
        
    }
    
    public  void connect() {
          try {
            ServerSocket serverSock = new ServerSocket(4242);
            
            while (true) {
                Socket sock = serverSock.accept();
                writer = new PrintWriter(sock.getOutputStream());
                reader = new BufferedReader(new InputStreamReader(sock.getInputStream()));
                System.out.println("NEtowrking established");
                
             }
        } catch (IOException ex) {
           ex.printStackTrace();
        }
          System.out.println("connect finished");
        
    }

        public class IncomingReader implements Runnable {
            public void run() {
                System.out.println("this far");
            try {
                
                String result = reader.readLine();
                
                reader.close();
                
                System.out.println("read " + result);
                writer.close();
            } catch (IOException ex) {
                ex.printStackTrace();
            }
            }
        }

        public class OutgoingWriter implements Runnable {
            public void run() {
                try {
                writer.println("hello");
                System.out.println("Written");
                Thread.sleep(2000);
                        
                
                } catch (Exception ex) {
                    ex.printStackTrace();
                }
                              
            }
        }
}

ChatClient.java

/*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.Socket;

/**
 *
 * @author Rob
 */
public class ChatClient {

    BufferedReader reader;
    PrintWriter writer;
    Socket sock;

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        ChatClient client = new ChatClient();
        client.SetUpNetworking();
    }

    private void SetUpNetworking() {
        try {
            sock = new Socket("127.0.0.1", 4242);
            InputStreamReader streamReader = new InputStreamReader(sock.getInputStream());
            reader = new BufferedReader(streamReader);
            writer = new PrintWriter(sock.getOutputStream());
            System.out.println("Netowrking Established");
            Thread readerThread = new Thread(new IncomingReader(reader));
            Thread writerThread = new Thread(new OutgoingWriter(writer));
            readerThread.start();
            writerThread.start();
        } catch (Exception ex) {
            ex.printStackTrace();
        }
    }
    class IncomingReader implements Runnable{
        private BufferedReader reader;
        
        public IncomingReader(BufferedReader reader) {
        this.reader = reader;
    }
        
            public void run() {   
            try {   
                String result = reader.readLine();   
                reader.close();   
                System.out.println("read " + result);   
                   
            } catch (IOException ex) {   
                ex.printStackTrace();   
            }   
        
    }
    }
            public class OutgoingWriter implements Runnable {   
            private PrintWriter writer;

            public OutgoingWriter(PrintWriter writer) {
                this.writer = writer;
            }

            public void run() {   
                writer.println("hello");   
                writer.flush();
                System.out.println("Written");   
                }   
                                 
            }   
    }

Output:
ChatServer:
hello
NEtowrking established
ChatClient:

Netowrking Established
Written

[Norm]

neither is printed.

That means those statements were never executed.
I think they do need to be executed, so you need to see why they weren't

[space.puffin]

Thanks again Norm.

If it runs fine on your machine is it not an environment problem. I've tried running the files on windows and linux to no avail. As for the threads not running i have no idea why they don't.

[Norm]

Have you looked at your code to see why this print statement is NOT being executed?

System.out.println("going to start thread");