NIO在網絡服務器中的樣例

 jdk供的無阻塞I/O（NIO）有效解決了多線程服務器存在的線程開銷問題，但在使用上略顯得複雜一些。在NIO中使用多線程，主要目的已不是爲了應對每個客戶端請求而分配獨立的服務線程，而是通過多線程充分使用用多個CPU的處理能力和處理中的等待時間，達到提高服務能力的目的。
    這段時間在研究NIO，寫篇博客來記住學過的東西。還是從最簡單的Hello World開始，
client多線程請求server端，server接收client的名字，並返回Hello! ＋名字的字符格式給client。當然實際應用並不這麼簡單，實際可能是訪問文件或者數據庫獲取信息返回給client。非阻塞的NIO有何神祕之處？代碼：

1)server端代碼

/**
 * 
 * @author Jeff
 *
 */
public class HelloWorldServer {

	static int BLOCK = 1024;
	static String name = "";
	protected Selector selector;
	protected ByteBuffer clientBuffer = ByteBuffer.allocate(BLOCK);
	protected CharsetDecoder decoder;
	static CharsetEncoder encoder = Charset.forName("GB2312").newEncoder();

	public HelloWorldServer(int port) throws IOException {
		selector = this.getSelector(port);
		Charset charset = Charset.forName("GB2312");
		decoder = charset.newDecoder();
	}

	// 獲取Selector
	protected Selector getSelector(int port) throws IOException {
		ServerSocketChannel server = ServerSocketChannel.open();
		Selector sel = Selector.open();
		server.socket().bind(new InetSocketAddress(port));
		server.configureBlocking(false);
		server.register(sel, SelectionKey.OP_ACCEPT);
		return sel;
	}

	// 監聽端口
	public void listen() {
		try {
			for (;;) {
				selector.select();
				Iterator iter = selector.selectedKeys().iterator();
				while (iter.hasNext()) {
					SelectionKey key = (SelectionKey) iter.next();
					iter.remove();
					process(key);
				}
			}
		} catch (IOException e) {
			e.printStackTrace();
		}
	}

	// 處理事件
	protected void process(SelectionKey key) throws IOException {
		if (key.isAcceptable()) { // 接收請求
			ServerSocketChannel server = (ServerSocketChannel) key.channel();
			SocketChannel channel = server.accept();
			//設置非阻塞模式
			channel.configureBlocking(false);
			channel.register(selector, SelectionKey.OP_READ);
		} else if (key.isReadable()) { // 讀信息
			SocketChannel channel = (SocketChannel) key.channel();
			int count = channel.read(clientBuffer);
			if (count > 0) {
				clientBuffer.flip();
				CharBuffer charBuffer = decoder.decode(clientBuffer);
				name = charBuffer.toString();
				// System.out.println(name);
				SelectionKey sKey = channel.register(selector,
						SelectionKey.OP_WRITE);
				sKey.attach(name);
			} else {
				channel.close();
			}

			clientBuffer.clear();
		} else if (key.isWritable()) { // 寫事件
			SocketChannel channel = (SocketChannel) key.channel();
			String name = (String) key.attachment();
			
			ByteBuffer block = encoder.encode(CharBuffer
					.wrap("Hello !" + name));
			

			channel.write(block);

			//channel.close();

		}
	}

	public static void main(String[] args) {
		int port = 8888;
		try {
			HelloWorldServer server = new HelloWorldServer(port);
			System.out.println("listening on " + port);
			
			server.listen();
			
		} catch (IOException e) {
			e.printStackTrace();
		}
	}
}

server主要是讀取client發過來的信息，並返回一條信息

2)client端代碼

/**
 * 
 * @author Jeff
 *
 */
public class HelloWorldClient {

	static int SIZE = 10;
	static InetSocketAddress ip = new InetSocketAddress("localhost", 8888);
	static CharsetEncoder encoder = Charset.forName("GB2312").newEncoder();

	static class Message implements Runnable {
		protected String name;
		String msg = "";

		public Message(String index) {
			this.name = index;
		}

		public void run() {
			try {
				long start = System.currentTimeMillis();
				//打開Socket通道
				SocketChannel client = SocketChannel.open();
				//設置爲非阻塞模式
				client.configureBlocking(false);
				//打開選擇器
				Selector selector = Selector.open();
				//註冊連接服務端socket動作
				client.register(selector, SelectionKey.OP_CONNECT);
				//連接
				client.connect(ip);
				//分配內存
				ByteBuffer buffer = ByteBuffer.allocate(8 * 1024);
				int total = 0;

				_FOR: for (;;) {
					selector.select();
					Iterator iter = selector.selectedKeys().iterator();

					while (iter.hasNext()) {
						SelectionKey key = (SelectionKey) iter.next();
						iter.remove();
						if (key.isConnectable()) {
							SocketChannel channel = (SocketChannel) key
									.channel();
							if (channel.isConnectionPending())
								channel.finishConnect();
							channel
									.write(encoder
											.encode(CharBuffer.wrap(name)));

							channel.register(selector, SelectionKey.OP_READ);
						} else if (key.isReadable()) {
							SocketChannel channel = (SocketChannel) key
									.channel();
							int count = channel.read(buffer);
							if (count > 0) {
								total += count;
								buffer.flip();

								while (buffer.remaining() > 0) {
									byte b = buffer.get();
									msg += (char) b;
									
								}

								buffer.clear();
							} else {
								client.close();
								break _FOR;
							}
						}
					}
				}
				double last = (System.currentTimeMillis() - start) * 1.0 / 1000;
				System.out.println(msg + "used time :" + last + "s.");
				msg = "";
			} catch (IOException e) {
				e.printStackTrace();
			}
		}
	}

	public static void main(String[] args) throws IOException {
	
		String names[] = new String[SIZE];

		for (int index = 0; index < SIZE; index++) {
			names[index] = "jeff[" + index + "]";
			new Thread(new Message(names[index])).start();
		}
	
	}
}