Java NIO之選擇就緒模式

   Java NIO出現不只是一個技術性能的提高，你會發現網絡上到處在介紹它，因爲它具有里程碑意義，從JDK1.4開始，Java開始提高性能相關的功能，從而使得Java在底層或者並行分佈式計算等操作上已經可以和C或Perl等語言並駕齊驅。

    Java　NIO非堵塞應用通常適用用在I/O讀寫等方面，我們知道，系統運行的性能瓶頸通常在I/O讀寫，包括對端口和文件的操作上，過去，在打開一個I/O通道後，read()將一直等待在端口一邊讀取字節內容，如果沒有內容進來，read()也是傻傻的等，這會影響我們程序繼續做其他事情，那麼改進做法就是開設線程，讓線程去等待，但是這樣做也是相當耗費資源的。

    Java NIO非堵塞技術實際是採取Reactor模式，或者說是Observer模式爲我們監察I/O端口，如果有內容進來，會自動通知我們，這樣，我們就不必開啓多個線程死等，從外界看，實現了流暢的I/O讀寫，不堵塞了。

    Java NIO出現不只是一個技術性能的提高，你會發現網絡上到處在介紹它，因爲它具有里程碑意義，從JDK1.4開始，Java開始提高性能相關的功能，從而使得Java在底層或者並行分佈式計算等操作上已經可以和C或Perl等語言並駕齊驅。

圖 1 類結構圖

 

package cn.chenkangxian.nioconcurrent;

import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.SelectionKey;
import java.nio.channels.SocketChannel;
import java.util.LinkedList;
import java.util.List;

/**
 * @Project: testNio
 * 
 * @Author: chenkangxian
 * 
 * @Annotation: 使用線程池來處理大量channel併發
 * 
 * @Date:2011-7-5
 * 
 * @Copyright: 2011 chenkangxian, All rights reserved.
 * 
 */
public class SelectSocketsThreadPool extends SelectSockets {

	private static final int MAX_THREADS = 5;
	private ThreadPool pool = new ThreadPool(MAX_THREADS);

	/**
	 * 從socket中讀數據
	 */
	protected void readDataFromSocket(SelectionKey key) throws Exception {

		WorkerThread worker = pool.getWorker();
		if (worker == null) {
			return;
		}

		worker.serviceChannel(key);
	}

	/**
	 *  
	 * @Project: concurrentnio
	 *
	 * @Author: chenkangxian
	 *
	 * @Annotation:線程池
	 *
	 * @Date:2011-7-20
	 *
	 * @Copyright: 2011 chenkangxian, All rights reserved.
	 *
	 */
	private class ThreadPool {

		List idle = new LinkedList();

		/**
		 * 線程池初始化
		 * 
		 * @param poolSize 線程池大小
		 */
		ThreadPool(int poolSize) {
			for (int i = 0; i < poolSize; i++) {
				WorkerThread thread = new WorkerThread(this);

				thread.setName("Worker" + (i + 1));
				thread.start();
				idle.add(thread);
			}
		}

		/**
		 * 獲得工作線程
		 * 
		 * Author: chenkangxian
		 *
		 * Last Modification Time: 2011-7-20
		 *
		 * @return
		 */
		WorkerThread getWorker() {
			WorkerThread worker = null;

			synchronized (idle) {
				if (idle.size() > 0) {
					worker = (WorkerThread) idle.remove(0);
				}
			}

			return (worker);
		}

		/**
		 * 送回工作線程
		 * 
		 * Author: chenkangxian
		 *
		 * Last Modification Time: 2011-7-20
		 *
		 * @param worker
		 */
		void returnWorker(WorkerThread worker) {
			synchronized (idle) {
				idle.add(worker);
			}
		}
	}

	private class WorkerThread extends Thread {

		private ByteBuffer buffer = ByteBuffer.allocate(1024);
		private ThreadPool pool;
		private SelectionKey key;

		WorkerThread(ThreadPool pool) {
			this.pool = pool;
		}

		public synchronized void run() {
			System.out.println(this.getName() + " is ready");
			while (true) {
				try {
					this.wait();//等待被notify
				} catch (InterruptedException e) {
					e.printStackTrace();
					this.interrupt();
				}

				if (key == null) {//直到有key
					continue;
				}

				System.out.println(this.getName() + " has been awakened");

				try {
					drainChannel(key);
				} catch (Exception e) {
					System.out.println("Caught '" + e + "' closing channel");

					try {
						key.channel().close();
					} catch (IOException ex) {
						ex.printStackTrace();
					}

					key.selector().wakeup();
				}

				key = null;

				this.pool.returnWorker(this);
			}
		}

		synchronized void serviceChannel(SelectionKey key) {
			this.key = key;
			
			//消除讀的關注
			key.interestOps(key.interestOps() & (~SelectionKey.OP_READ));
			this.notify();
		}

		void drainChannel(SelectionKey key) throws Exception {

			SocketChannel channel = (SocketChannel) key.channel();
			int count;

			buffer.clear(); 

			while ((count = channel.read(buffer)) > 0) {
				buffer.flip();

				while (buffer.hasRemaining()) {
					channel.write(buffer);
				}

				buffer.clear();
			}

			if (count < 0) {
				channel.close();
				return;
			}
			
			//重新開始關注讀事件
			key.interestOps(key.interestOps() | SelectionKey.OP_READ);

			key.selector().wakeup();
		}

	}

	public static void main(String[] args) throws Exception {

		new SelectSocketsThreadPool().go(args);

	}
}

 

package cn.chenkangxian.nioconcurrent;

import java.net.InetSocketAddress;
import java.net.ServerSocket;
import java.nio.ByteBuffer;
import java.nio.channels.SelectableChannel;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.ServerSocketChannel;
import java.nio.channels.SocketChannel;
import java.util.Iterator;

/**
 * 
 * @Project: concurrentnio
 *
 * @Author: chenkangxian
 *
 * @Annotation: 
 *
 * @Date:2011-7-11
 *
 * @Copyright: 2011 chenkangxian, All rights reserved.
 *
 */
public class SelectSockets {

	public static int PORT_NUMBER = 1234;
	
	private ByteBuffer buffer = ByteBuffer.allocate(1024);
	
	public static void main(String[] args) throws Exception {

		new SelectSockets().go(args);

	}
	
	public void go(String[] args) throws Exception{
		
		int port = PORT_NUMBER;
//		if(args.length > 0){
//			port = Integer.parseInt(args[0]);
//		}
//		System.out.println("Listening on port " + port);
		
		ServerSocketChannel serverChannel = ServerSocketChannel.open();
		
		ServerSocket serverSocket = serverChannel.socket();
		
		Selector selector = Selector.open();
		
		serverSocket.bind(new InetSocketAddress(port));
		
		serverChannel.configureBlocking(false);
		
		serverChannel.register(selector, SelectionKey.OP_ACCEPT);
		
		while(true){

			int n = selector.select(); //沒有輪詢，單個selector
			
			if(n == 0){
				continue; 
			}
			
			Iterator it = selector.selectedKeys().iterator();
			
			while(it.hasNext()){
				SelectionKey key = (SelectionKey)it.next();
				
				if(key.isAcceptable()){
					ServerSocketChannel server = 
						(ServerSocketChannel)key.channel();
					SocketChannel channel = server.accept();
					
					registerChannel(selector,channel
							,SelectionKey.OP_READ);
					
					sayHello(channel);
				}
				
				if(key.isReadable()){
					readDataFromSocket(key);
				}
				
				it.remove();
			}
		}
		
	}
	
	
	/**
	 * 在selector上註冊channel，並設置interest
	 * 
	 * Author: chenkangxian
	 *
	 * Last Modification Time: 2011-7-11
	 *
	 * @param selector 選擇器
	 * 
	 * @param channel 通道
	 * 
	 * @param ops interest
	 * 
	 * @throws Exception
	 */
	protected void registerChannel(Selector selector,
			SelectableChannel channel, int ops) throws Exception{
		
		if(channel == null){
			return ; 
		}
		
		channel.configureBlocking(false);
		
		channel.register(selector, ops);
	}
	
	
	
	
	/**
	 * 處理有可用數據的通道
	 * 
	 * Author: chenkangxian
	 *
	 * Last Modification Time: 2011-7-11
	 *
	 * @param key 可用通道對應的key
	 * 
	 * @throws Exception
	 */
	protected void readDataFromSocket(SelectionKey key) throws Exception{
		
		SocketChannel socketChannel = (SocketChannel)key.channel();
		int count;
		
		buffer.clear(); //Empty buffer
		
		while((count = socketChannel.read(buffer)) > 0){
			
			buffer.flip(); 
			
			while(buffer.hasRemaining()){
				socketChannel.write(buffer);
			}
			
			buffer.clear(); 
			
		}
		
		if(count < 0){
			socketChannel.close();
		}
		
	}
	
	/**
	 * 打招呼
	 * 
	 * Author: chenkangxian
	 *
	 * Last Modification Time: 2011-7-11
	 *
	 * @param channel 客戶端channel
	 * 
	 * @throws Exception
	 */
	private void sayHello(SocketChannel channel) throws Exception{
		
		buffer.clear();
		buffer.put("Hello 哈羅! \r\n".getBytes());
		buffer.flip();
		
		channel.write(buffer);
	}

}