Java Socket not working on LAN

Question

There are two computers, A and B, each one of them is waiting for the other one to tell him that is ready, when they receive the message they'll start doing something.

public class SyncClientImpl implements SyncClient, Runnable {

private Socket s;
private String ipAddress;
private int port;
private boolean otherIsReady;
private Thread thread;
private OutputStream os;
private ObjectOutputStream oos;

public Thread getThread() {
    return thread;
}

public void setThread(Thread thread) {
    this.thread = thread;
}

public void start() {
    thread = new Thread(this);
    thread.start();
}

public boolean isOtherIsReady() {
    return otherIsReady;
}

public void setOtherIsReady(boolean otherIsReady) {
    this.otherIsReady = otherIsReady;
}

public Socket getS() {
    if (s == null) {
        try {
            s = new Socket(ipAddress, port);
        } catch (UnknownHostException ex) {
            Logger.getLogger(SyncClientImpl.class.getName()).log(Level.SEVERE, null, ex);
        } catch (IOException ex) {
            Logger.getLogger(SyncClientImpl.class.getName()).log(Level.SEVERE, null, ex);
        }
    }
    return s;
}

public void setS(Socket s) {
    this.s = s;
}

public String getIpAddress() {
    return ipAddress;
}

public void setIpAddress(String ipAddress) {
    this.ipAddress = ipAddress;
}

public int getPort() {
    return port;
}

public void setPort(int port) {
    this.port = port;
}

@Override
public void send(Object o, int port, String ipAdrress) {
    try {
        os = this.getS().getOutputStream();
        oos = new ObjectOutputStream(os);
        oos.flush();
        oos.writeObject(o);
        oos.flush();
    } catch (IOException ex) {
        Logger.getLogger(SyncClientImpl.class.getName()).log(Level.SEVERE, null, ex);
    }
}

@Override
public void update() {
    otherIsReady = true;
}

@Override
public void run() {
    try {
        while (!otherIsReady) {
            try {
                this.send("ready", port, ipAddress);
                Thread.sleep(500);
            } catch (InterruptedException ex) {
                Logger.getLogger(SyncClientImpl.class.getName()).log(Level.SEVERE, null, ex);
            }
        }
        oos.close();
        os.close();
        s.close();
    } catch (IOException ex) {
        Logger.getLogger(SyncClientImpl.class.getName()).log(Level.SEVERE, null, ex);
    }
}
}

This first class sends the message "ready" to a server, it will stop doing it until someone else notify it. The class that will notify it is this one:

public class SyncServerImpl implements SyncServer, Runnable {

private ServerSocket ss;
private Socket s;
private String ipAddress;
private int port;
private InputStream is;
private ObjectInputStream ois;
private boolean confirmReceived;
private Thread thread;
private transient List<Observer> list = new ArrayList<Observer>();
private Object lock;

public boolean isConfirmReceived() {
    return confirmReceived;
}

public void setConfirmReceived(boolean confirmReceived) {
    this.confirmReceived = confirmReceived;
}

@Override
public void setLock(Object lock) {
    this.lock = lock;
}

public void start() {
    thread = new Thread(this);
    thread.start();
}

public Socket getS() {
    if (s == null) {
        try {
            s = this.getSS().accept();
        } catch (UnknownHostException ex) {
            Logger.getLogger(SyncClientImpl.class.getName()).log(Level.SEVERE, null, ex);
        } catch (IOException ex) {
            Logger.getLogger(SyncClientImpl.class.getName()).log(Level.SEVERE, null, ex);
        }
    }
    return s;
}

public void setS(Socket s) {
    this.s = s;
}

public String getIpAddress() {
    return ipAddress;
}

public void setIpAddress(String ipAddress) {
    this.ipAddress = ipAddress;
}

public int getPort() {
    return port;
}

public void setPort(int port) {
    this.port = port;
}

public ServerSocket getSS() {
    if (ss == null) {
        try {
            ss = new ServerSocket(port);
        } catch (IOException ex) {
            Logger.getLogger(SyncServerImpl.class.getName()).log(Level.SEVERE, null, ex);
        }
    }
    return ss;
}

public void setSS(ServerSocket ss) {
    this.ss = ss;
}

@Override
public void addObserver(Observer observer) {
    list.add(observer);
}

@Override
public void removeObserver(Observer observer) {
    list.remove(observer);
}

@Override
public void notifyObservers() {
    for (Observer observer : list) {
        observer.update();
    }
}

public void receive() {
    try {
        is = this.getS().getInputStream();
        ois = new ObjectInputStream(is);
        String to = (String) ois.readObject();
        if (to.equalsIgnoreCase("ready")) {

            synchronized (lock) {
                confirmReceived = true;
                this.notifyObservers();
                lock.notifyAll();
            }
            System.out.println("packet received");

        }
    } catch (IOException ex) {
        Logger.getLogger(SyncServerImpl.class.getName()).log(Level.SEVERE, null, ex);
    } catch (ClassNotFoundException ex) {
        Logger.getLogger(SyncServerImpl.class.getName()).log(Level.SEVERE, null, ex);
    }
}

@Override
public void run() {
    try {
        while (!confirmReceived) {
            this.receive();
        }
        ois.close();
        is.close();
        s.close();
        ss.close();
    } catch (Exception ex) {
        Logger.getLogger(SyncServerImpl.class.getName()).log(Level.SEVERE, null, ex);
    }
}

public static void main(String args[]) {
    final Object lock = new Object();
    SyncServerImpl ss = new SyncServerImpl();
    SyncClientImpl sc = new SyncClientImpl();
    ss.setLock(lock);
    ss.addObserver(sc);
    ss.setPort(2002);
    ss.start();


    sc.setIpAddress("192.168.1.101");
    sc.setPort(2002);
    sc.start();

    synchronized (lock) {
        while (!ss.isConfirmReceived()) {
            try {
                lock.wait();
            } catch (InterruptedException ex) {
            }
        }
    }

    System.out.println("Ok");
}
}

This Server is waiting for the message "ready" to arrive, when it comes it will notify the other class which will stop sending packets, and will notify the main thread waiting on the lock. It works fine on the localhost but not on my LAN. I have a mac and a pc, if I start the main method first from the pc and then from the mac, I get this error (from the mac, which will iterate endlessly).

sync.SyncClientImpl send
GRAVE: null
java.net.SocketException: Broken pipe
at java.net.SocketOutputStream.socketWrite0(Native Method)
at java.net.SocketOutputStream.socketWrite(SocketOutputStream.java:92)
at java.net.SocketOutputStream.write(SocketOutputStream.java:136)
at java.io.ObjectOutputStream$BlockDataOutputStream.drain(ObjectOutputStream.java:1864)
at java.io.ObjectOutputStream$BlockDataOutputStream.setBlockDataMode(ObjectOutputStream.java:1773)
at java.io.ObjectOutputStream.<init>(ObjectOutputStream.java:229)
at tetris.logic.online.sync.SyncClientImpl.send(SyncClientImpl.java:87)
at tetris.logic.online.sync.SyncClientImpl.run(SyncClientImpl.java:106)
at java.lang.Thread.run(Thread.java:695)

while of the pc it reports me that the connection is refused (but it's ok because it starts first)

If I start first on the mac and the on the pc, I get this error (from the pc) which will iterate endlessly too:

sync.SyncClientImpl send
GRAVE: null
java.net.SocketException: Software caused connection abort: socket write error
...
at tetris.logic.online.sync.SyncClientImpl.send(SyncClientImpl.java:87)
at tetris.logic.online.sync.SyncClientImpl.run(SyncClientImpl.java:106)
at java.lang.Thread.run(Thread.java:695)

This error looks like to be the same of one above but described in a different manner.

Does any one knows what is causing this error?

Don't create a new `ObjectOutputStream` for every send. Create it once for the life of the socket. Ditto the `ObjectInputStream.` — user207421, Dec 01 '13 at 22:42

score 0 · Answer 1 · answered Dec 01 '13 at 22:15

Try to simplify your solution, and take a look at the following article on socket programming: Writing the Server Side of a Socket.

Try to make it work one way first before attempting to do it in both directions (although the need for that feature isn't quite clear to me). Right now the client & server threads within the same applications are interfering with the client/server pair you're trying to set up over the network.

If you only want to send text over the socket just use BufferedReader and PrintWriter instead of ObjectStreams (latter could get you into memory issues if not managed properly).

@Override
public void send(String line, int port, String ipAdrress) {
    try {
        Socket clientSocket = new Socket(ipAddress, port);
        os = clientSocket.getOutputStream();
        PrintWriter out= new PrintWriter(os, true);
        out.println(line);
        out.close();
        clientSocket.close();
    } catch (IOException ex) {
        Logger.getLogger(SyncClientImpl.class.getName()).log(Level.SEVERE, null, ex);
    }
}

If you only want to use the connection for checking if the other is ready than closing the Socket is ok, but if you'd want to keep the connection open you need to keep the OutputStream (not the Socket itself) for further processing in the Thread. Again, take a look at the article above and work from there.

Java Socket not working on LAN

1 Answers1