解读NIO Socket非阻塞模式

[color=darkblue]前言：[/color]
jdk供的无阻塞I/O（NIO）有效解决了多线程服务器存在的线程开销问题，但在使用上略显得复杂一些。在NIO中使用多线程，主要目的已不是为了应对每个客户端请求而分配独立的服务线程，而是通过多线程充分使用用多个CPU的处理能力和处理中的等待时间，达到提高服务能力的目的。
这段时间在研究NIO，写篇博客来记住学过的东西。还是从最简单的Hello World开始，
client多线程请求server端，server接收client的名字，并返回Hello! ＋名字的字符格式给client。当然实际应用并不这么简单，实际可能是访问文件或者数据库获取信息返回给client。非阻塞的NIO有何神秘之处？代码：

1)server端代码

/**
 * 
 * @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();
	}

	// 获取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;
	}

	// 监听端口
	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();
		}
	}

	// 处理事件
	protected void process(SelectionKey key) throws IOException {
		if (key.isAcceptable()) { // 接收请求
			ServerSocketChannel server = (ServerSocketChannel) key.channel();
			SocketChannel channel = server.accept();
			//设置非阻塞模式
			channel.configureBlocking(false);
			channel.register(selector, SelectionKey.OP_READ);
		} else if (key.isReadable()) { // 读信息
			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()) { // 写事件
			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主要是读取client发过来的信息，并返回一条信息

2)client端代码

/**
 * 
 * @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();
				//打开Socket通道
				SocketChannel client = SocketChannel.open();
				//设置为非阻塞模式
				client.configureBlocking(false);
				//打开选择器
				Selector selector = Selector.open();
				//注册连接服务端socket动作
				client.register(selector, SelectionKey.OP_CONNECT);
				//连接
				client.connect(ip);
				//分配内存
				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();
		}

	}
}