The document describes how to use the reactor pattern with Java NIO to handle server connections and client events asynchronously. It involves using a selector to register channels for accepting new connections, reading from existing connections, and writing to connections. For each I/O event detected by the selector, the appropriate handler is notified to process the event and the selector then returns to listening for more events. This allows for non-blocking and scalable handling of multiple clients simultaneously.

1. Reactor Design Pattern(Using java nio)By: Allan S. Lim

2. SelectorSelector selector = Selector.open();

3. SelectorsscServerSocketChannelssc = ServerSocketChannel.open();ssc.configureBlocking( false );ServerSocketss = ssc.socket();InetSocketAddress address = new InetSocketAddress(port);ss.bind( address );

4. registerSelectorsscacceptSelectionKey key = ssc.register( selector, SelectionKey.OP_ACCEPT );

5. registeraccept handlerSelectorsscacceptint num = selector.select();Set selectedKeys = selector.selectedKeys();Iterator it = selectedKeys.iterator();while (it.hasNext()) {SelectionKey key = (SelectionKey)it.next(); if ((key.readyOps() & SelectionKey.OP_ACCEPT) == SelectionKey.OP_ACCEPT) { // Accept the new connection and send to a handler. }}

6. registeraccept handlerSelectorsscacceptreadscreadhandlerServerSocketChannelssc = (ServerSocketChannel)key.channel();SocketChannel sc = ssc.accept();sc.configureBlocking( false );SelectionKeynewKey = sc.register( selector, SelectionKey.OP_READ );

7. registeraccept handlerSelectorsscacceptreadscreadhandler if ((key.readyOps() & SelectionKey.OP_ACCEPT) == SelectionKey.OP_ACCEPT) { // Accept the new connection and send to a handler. } else if ((key.readyOps() & SelectionKey.OP_READ) == SelectionKey.OP_READ) { // Read the data and send the handler.SocketChannelsc = (SocketChannel)key.channel();}

8. registeraccept handlerSelectorsscacceptreadscreadhandlerwritescwritehandlerIt’s the same process with the write handler.

9. registeraccept handlerSelectorsscacceptreadscreadhandlerwritescwritehandlerYou can have an array of handlers.

10. CLIENTSregisteraccept handlerSelectorsscacceptreadscreadhandlerwritescwritehandlerFor each client event, the selector will notify the handler, and return to listening to event again.