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Sockets

Posted on 2009-07-12
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Last Modified: 2012-05-07
I have written a simple client server program using sockets. There is no compilation and run time error. However the application does not seem to do the logics I have written. Did I miss something?.
Client
-------
 
import java.io.*;
import java.net.*;
 
public class Client
{
	Socket s;
	PrintWriter out;
	BufferedReader in;
	
	public Client()
	{
		try
		{ 
	        s = new Socket("127.0.0.1",1418);
	        out = new PrintWriter(s.getOutputStream());
	        in = new BufferedReader(new InputStreamReader(s.getInputStream()));
	        out.write("Hi");
	        String m = in.readLine();
	        System.out.println(m);
		}
		catch(Exception e)
		{
			System.out.println(e);
		}
	}
	 
    public static void main(String[] args) 
    {
        Client m = new Client();
    }
}
 
 
Server
---------
 
public class Server 
{
	PrintWriter out;
	BufferedReader in;
	ServerSocket ss;
	Socket sc;
	
	public Server()
	{
		try
		{
			ss = new ServerSocket(1418);
			sc = ss.accept();
			out = new PrintWriter(sc.getOutputStream());
			in = new BufferedReader(new InputStreamReader(sc.getInputStream()));
			String m = in.readLine();
			out.write(m);
		}
		catch(Exception e)
		{
			System.out.println(e);
		}
	}
	
    public static void main(String[] args) 
    {
    	Server s = new Server();
    }
}

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Question by:eugene007
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10 Comments
 
LVL 8

Assisted Solution

by:ozlevanon
ozlevanon earned 20 total points
ID: 24834421
Your client is writing just 2 characters "hi", but the server is inovking readLine, which waits for a newline character before it returns.
If you change you client to write "hi\n" it will probably fix it. Also, pay attention that calling write() method doesn't guarantee that the data will be flushed, so in any event, call flush() when you want to make sure the data is actually written.
0
 

Author Comment

by:eugene007
ID: 24834545
I tried and it does not work.
0
 

Author Comment

by:eugene007
ID: 24834566
Also I switched write() method to println() method.
0
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LVL 23

Assisted Solution

by:Ajay-Singh
Ajay-Singh earned 20 total points
ID: 24834583
Try flush after you write to PrintWriter both on the client
and the server side.
0
 

Author Comment

by:eugene007
ID: 24834631
Now it works. This is quite odd. I need to flush the data even when im using the println() method to write.
0
 
LVL 86

Accepted Solution

by:
CEHJ earned 30 total points
ID: 24834891
>>I need to flush the data even when im using the println() method to write.

You won't do if you do

out = new PrintWriter(s.getOutputStream(), true);
0
 

Author Comment

by:eugene007
ID: 24836691
so the purpose of the flush() method is to ensure that what is written are commited.
0
 
LVL 23

Expert Comment

by:Ajay-Singh
ID: 24836950
Yes.
0
 
LVL 86

Expert Comment

by:CEHJ
ID: 24837757
>>so the purpose of the flush() method is to ensure that what is written are commited.

No. It's in no way transactional. There's no 'rollback' for instance. And when you close(), it will get flushed automatically.

Its purpose is to transfer what's held in the buffers to the stream immediately
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Expert Comment

by:CEHJ
ID: 24859071
:-)
0

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