Java client socket using writeBytes

Question

I'm reading a string from a buffer and writing it to a server. The problem I'm having is that the string never gets received by the server when I leave the socket open and write in a loop. When I use this:

    try {       
        Socket send = new Socket("localhost", 1490);
        DataOutputStream out = new DataOutputStream(send.getOutputStream());
        String message = null;
        while ((message = buffer.get()) != null){
            out.writeBytes(message);
        }
        out.close();
        send.close();
    } catch (IOException ex) {
        ex.printStackTrace();
    }
}

the server doesn't receive the string, but when I do this it works properly:

    try {       

        String message = null;
        while ((message = buffer.get()) != null){
            Socket send = new Socket("localhost", 1490);
            DataOutputStream out = new DataOutputStream(send.getOutputStream());
                    out.writeBytes(message);
            out.close();
            send.close();
        }

    } catch (IOException ex) {
        ex.printStackTrace();
    }
}

Obviously I don't want to keep opening and closing the socket, though. What is the problem?

GETah · Accepted Answer · 2012-02-18 14:32:13Z

1

You need to flush your socket every time you want to send a data packet. Closing a socket forces an automatic flush and that explains why your data is getting sent on socket close.

answered Feb 18, 2012 at 14:32

GETah

21.5k7 gold badges67 silver badges110 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Nitzan Tomer · Accepted Answer · 2012-02-18 14:18:31Z

0

The data is not being written to the socket even when you close it? (in your first snippet that is)

Also, have you tried to use the flush method? You can read about it here: http://docs.oracle.com/javase/1.4.2/docs/api/java/io/DataOutputStream.html#flush() and your code will look like:

try {       
    Socket send = new Socket("localhost", 1490);
    DataOutputStream out = new DataOutputStream(send.getOutputStream());
    String message = null;
    while ((message = buffer.get()) != null){
        out.writeBytes(message);
        out.flush();
    }
    out.close();
    send.close();
} catch (IOException ex) {
    ex.printStackTrace();
}

answered Feb 18, 2012 at 14:18

Nitzan Tomer

166k51 gold badges330 silver badges307 bronze badges

1 Comment

user1190650 Over a year ago

Yes, I did try flush and I still have the same problem. The buffer always has strings, so I don't think the socket actually closes. But why are my message still not received?

Stephen C · Accepted Answer · 2012-02-18 14:33:34Z

0

Let me make a guess.

Does the buffer.get() method block? If so, then the problem is that out.writeBytes(message) does not guarantee that the entire byte representation to be pushed to the server. Instead. there is a good chance that your client has buffered bytes waiting to be flushed through to the server.

If this is what is going on, then calling flush after each call to writeBytes will fix the problem.

But if the buffer.get() method doesn't block, then calling flush won't make any difference. In fact, it will just increase the network traffic. So adding the flush "just in case" is a bad idea.

Another possibility is that there is something wrong with the server-side code.

answered Feb 18, 2012 at 14:33

Stephen C

723k95 gold badges849 silver badges1.3k bronze badges

1 Comment

user1190650 Over a year ago

Thanks. Yes, buffer.get() does block, but I did try flushing the buffer after each call to writeBytes and I still have the same problem. Any other ideas?

Collectives™ on Stack Overflow

Java client socket using writeBytes

3 Answers 3

Comments

1 Comment

1 Comment

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

1 Comment

1 Comment

Your Answer

Sign up or log in

Post as a guest

Linked

Related