File	Doc	Category	Size	Date	Package
SelectSockets.java	API Doc	Example	5125	Mon May 20 00:24:28 BST 2002	com.ronsoft.books.nio.channels

SelectSockets

• java.lang.Object

Fields Summary
public static int	PORT_NUMBER
private ByteBuffer	buffer

Constructors Summary

Methods Summary
public void	go(java.lang.String[] argv) 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(); } }
public static void	main(java.lang.String[] argv) new SelectSockets().go (argv);
protected void	readDataFromSocket(java.nio.channels.SelectionKey key) 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. 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(); }
protected void	registerChannel(java.nio.channels.Selector selector, java.nio.channels.SelectableChannel channel, int ops) Register the given channel with the given selector for the given operations of interest if (channel == null) { return; // could happen } // set the new channel non-blocking channel.configureBlocking (false); // register it with the selector channel.register (selector, ops);
private void	sayHello(java.nio.channels.SocketChannel channel) Spew a greeting to the incoming client connection. param channel The newly connected SocketChannel to say hello to. buffer.clear(); buffer.put ("Hi there!\r\n".getBytes()); buffer.flip(); channel.write (buffer);