package com.ronsoft.books.nio.channels;
import java.nio.ByteBuffer;
import java.nio.channels.ServerSocketChannel;
import java.nio.channels.SocketChannel;
import java.nio.channels.Selector;
import java.nio.channels.SelectionKey;
import java.nio.channels.SelectableChannel;
import java.net.Socket;
import java.net.ServerSocket;
import java.net.InetSocketAddress;
import java.util.Iterator;
/**
* Simple echo-back server which listens for incoming stream connections
* and echoes back whatever it reads. A single Selector object is used to
* listen to the server socket (to accept new connections) and all the
* active socket channels.
*
* @author Ron Hitchens (ron@ronsoft.com)
* @version $Id: SelectSockets.java,v 1.5 2002/05/20 07:24:29 ron Exp $
*/
public class SelectSockets
{
public static int PORT_NUMBER = 1234;
public static void main (String [] argv)
throws Exception
{
new SelectSockets().go (argv);
}
public void go (String [] argv)
throws Exception
{
int port = PORT_NUMBER;
if (argv.length > 0) { // override default listen port
port = Integer.parseInt (argv [0]);
}
System.out.println ("Listening on port " + port);
// allocate an unbound server socket channel
ServerSocketChannel serverChannel = ServerSocketChannel.open();
// Get the associated ServerSocket to bind it with
ServerSocket serverSocket = serverChannel.socket();
// create a new Selector for use below
Selector selector = Selector.open();
// set the port the server channel will listen to
serverSocket.bind (new InetSocketAddress (port));
// set non-blocking mode for the listening socket
serverChannel.configureBlocking (false);
// register the ServerSocketChannel with the Selector
serverChannel.register (selector, SelectionKey.OP_ACCEPT);
while (true) {
// this may block for a long time, upon return the
// selected set contains keys of the ready channels
int n = selector.select();
if (n == 0) {
continue; // nothing to do
}
// get an iterator over the set of selected keys
Iterator it = selector.selectedKeys().iterator();
// look at each key in the selected set
while (it.hasNext()) {
SelectionKey key = (SelectionKey) it.next();
// Is a new connection coming in?
if (key.isAcceptable()) {
ServerSocketChannel server =
(ServerSocketChannel) key.channel();
SocketChannel channel = server.accept();
registerChannel (selector, channel,
SelectionKey.OP_READ);
sayHello (channel);
}
// is there data to read on this channel?
if (key.isReadable()) {
readDataFromSocket (key);
}
// remove key from selected set, it's been handled
it.remove();
}
}
}
// ----------------------------------------------------------
/**
* Register the given channel with the given selector for
* the given operations of interest
*/
protected void registerChannel (Selector selector,
SelectableChannel channel, int ops)
throws Exception
{
if (channel == null) {
return; // could happen
}
// set the new channel non-blocking
channel.configureBlocking (false);
// register it with the selector
channel.register (selector, ops);
}
// ----------------------------------------------------------
// Use the same byte buffer for all channels. A single thread is
// servicing all the channels, so no danger of concurrent acccess.
private ByteBuffer buffer = ByteBuffer.allocateDirect (1024);
/**
* Sample data handler method for a channel with data ready to read.
* @param key A SelectionKey object associated with a channel
* determined by the selector to be ready for reading. If the
* channel returns an EOF condition, it is closed here, which
* automatically invalidates the associated key. The selector
* will then de-register the channel on the next select call.
*/
protected void readDataFromSocket (SelectionKey key)
throws Exception
{
SocketChannel socketChannel = (SocketChannel) key.channel();
int count;
buffer.clear(); // make buffer empty
// loop while data available, channel is non-blocking
while ((count = socketChannel.read (buffer)) > 0) {
buffer.flip(); // make buffer readable
// send the data, don't assume it goes all at once
while (buffer.hasRemaining()) {
socketChannel.write (buffer);
}
// WARNING: the above loop is evil. Because
// it's writing back to the same non-blocking
// channel it read the data from, this code can
// potentially spin in a busy loop. In real life
// you'd do something more useful than this.
buffer.clear(); // make buffer empty
}
if (count < 0) {
// close channel on EOF, invalidates the key
socketChannel.close();
}
}
// ----------------------------------------------------------
/**
* Spew a greeting to the incoming client connection.
* @param channel The newly connected SocketChannel to say hello to.
*/
private void sayHello (SocketChannel channel)
throws Exception
{
buffer.clear();
buffer.put ("Hi there!\r\n".getBytes());
buffer.flip();
channel.write (buffer);
}
}
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