How to make a Simple NIO Scalable Server?

Question

I want to learn NIO for a project, but first want to start out simple. I want to figure out how to send a string across from clients to a server using NIO. I tried looking up stuff, but got caught in the terminology and such. How can I make a simple scalable server (agh tripple S) to send strings across? (like a chat server or something). All I know is I need to use a Selector and some Threaded loops to do stuff.
I found http://gee.cs.oswego.edu/dl/cpjslides/nio.pdf and tweaked the code to make (what I thought was) a simple server, but I do not know how to make client code or even whether or not my Server code works.
This is what I have so far:
import java.io.*;
import java.nio.*;
import java.nio.channels.*;
import java.nio.channels.spi.*;
import java.net.*;
import java.util.*;
import static java.lang.System.*;
public class NIOTest {
public static void main(String args[]) throws Throwable
try {
new Thread(new NIOTestServer()).start();
} catch(Exception e) {
e.printStackTrace();       
class NIOTestServer implements Runnable
final Selector selector;
final ServerSocketChannel serverSocket;
int chatPort=9990;
public NIOTestServer() throws Exception
selector=Selector.open();
serverSocket = ServerSocketChannel.open();
serverSocket.socket().bind(
new InetSocketAddress(chatPort));
serverSocket.configureBlocking(false);
SelectionKey sk =
serverSocket.register(selector,
SelectionKey.OP_ACCEPT);
sk.attach(new Acceptor());
public void run()
try
while(!Thread.interrupted())
selector.select(); //Blocks until atleast one I/O event has occured
Iterator<SelectionKey> it=selector.selectedKeys().iterator();
while(it.hasNext())
dispatch(it.next());
catch(Throwable lol)
lol.printStackTrace();
void dispatch(SelectionKey k)
Runnable r = (Runnable)(k.attachment());
if (r != null)
r.run();
class Acceptor implements Runnable
{ // inner class to accept the event
public void run()
try
SocketChannel c = serverSocket.accept();
if (c != null)
new Handler(selector, c);
catch(IOException ex) {ex.printStackTrace();}
import java.io.*;
import java.nio.*;
import java.nio.channels.*;
import java.nio.channels.spi.*;
import java.net.*;
import java.util.*;
import static java.lang.System.*;
final class Handler implements Runnable {
final SocketChannel socket;
final SelectionKey sk;
ByteBuffer input = ByteBuffer.allocate(1024);
ByteBuffer output = ByteBuffer.allocate(1024);
static final byte READING = 0, SENDING = 1;
byte state = READING;
Handler(Selector sel, SocketChannel c) throws IOException
socket = c; c.configureBlocking(false); //makes it non blocking
// Optionally try first read now
sk = socket.register(sel, 0);
sk.attach(this);
sk.interestOps(SelectionKey.OP_READ);
sel.wakeup();
boolean inputIsComplete()
return input.hasRemaining();
boolean outputIsComplete()
return output.hasRemaining();
void process()
CharBuffer buf=input.asCharBuffer();
buf.flip();
out.println(buf);
public void run()
try {
if (state == READING) read();
else if (state == SENDING) send();
catch (IOException ex) { ex.printStackTrace(); }
void read() throws IOException
socket.read(input);
if (inputIsComplete())
process();
state = SENDING;
// Normally also do first write now
sk.interestOps(SelectionKey.OP_WRITE);
void send() throws IOException
socket.write(output);
if (outputIsComplete()) sk.cancel();
}again this is a rough incomplete code test.

Answer 1

See http://forum.java.sun.com/thread.jspa?forumID=536&threadID=5277053. You can use Telnet as a test client. When you come to write your own client, use java.net, not java.nio.