Java NIO Socket 非阻塞通信

相对于非阻塞通信的复杂性，通常客户端并不需要使用非阻塞通信以提高性能，故这里只有服务端使用非阻塞通信方式实现

客户端：

package com.test.client;

import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.net.InetAddress;
import java.net.InetSocketAddress;
import java.nio.channels.SocketChannel;

import org.apache.log4j.Logger;

import com.test.util.SocketIO;

public class Client {
	static Logger logger = Logger.getLogger(Client.class);
	private int port = 10000;
	private SocketChannel socketChannel;
	
	public Client(){
		try {
			socketChannel = SocketChannel.open();
			InetAddress host = InetAddress.getLocalHost();
			InetSocketAddress addr = new InetSocketAddress(host, port);
			
			socketChannel.connect(addr);
			
			logger.debug("***");
			logger.debug("client ip:"+socketChannel.socket().getLocalAddress());
			logger.debug("client port:"+socketChannel.socket().getLocalPort());
			logger.debug("server ip:"+socketChannel.socket().getInetAddress());
			logger.debug("server port:"+socketChannel.socket().getPort());
			logger.debug("***");
		} catch (IOException e) {
			e.printStackTrace();
			logger.error("Cilent socket establish failed!");
		}
		logger.info("Client socket establish success!");
	}
	
	public void request(String request){
		try{
			DataInputStream input = SocketIO.getInput(socketChannel.socket());
			DataOutputStream output = SocketIO.getOutput(socketChannel.socket());
			
			if(null != request && !request.equals("")){
				byte[] bytes = request.getBytes("utf-8");
				output.write(bytes);
		
				bytes = new byte[64];
				int num = input.read(bytes);
				byte[] answer = new byte[num];
				System.arraycopy(bytes, 0, answer, 0, num);
				if(num > 0){
					logger.info("server answer:"+new String(answer,"utf-8"));
				}else{
					logger.info("No server answer.");
				}
			}
		}catch(Exception e){
			e.printStackTrace();
			logger.error("client request error");
		}finally{
			if(null != socketChannel){
				try{
					socketChannel.close();
				}catch(Exception e){
					e.printStackTrace();
					logger.error("socket close error");
				}
			}
		}
	}
	
	public static void main(String[] args){
		Client client1 = new Client();
		//Client client2 = new Client();
		client1.request("your name?");
		//client2.request("your name?");
	}
}

服务端：

package com.test.server;

import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.ServerSocketChannel;
import java.nio.channels.SocketChannel;
import java.nio.charset.Charset;
import java.util.Iterator;
import java.util.Set;

import org.apache.log4j.Logger;

public class Server {
	static Logger logger = Logger.getLogger(Server.class);
	private Selector selector;
	private ServerSocketChannel serverSocketChannel;
	private int queueNum = 10;
	private int bindPort = 10000;
	private int step = 0;
	private Charset charset = Charset.forName("utf-8");
	private ByteBuffer buffer = ByteBuffer.allocate(64);
	
	public Server(){
		try{
			//为ServerSocketChannel监控接收连接就绪事件
			//为SocketChannel监控连接就绪事件、读就绪事件以及写就绪事件
			selector = Selector.open();
			//作用相当于传统通信中的ServerSocket
			//支持阻塞模式和非阻塞模式
			serverSocketChannel = ServerSocketChannel.open();
			serverSocketChannel.socket().setReuseAddress(true);
			//非阻塞模式
			serverSocketChannel.configureBlocking(false);
			//serverSocketChannel.socket()会获得一个和当前信道相关联的socket
			serverSocketChannel.socket().bind(new InetSocketAddress(bindPort),queueNum);
			
			//注册接收连接就绪事件
			//注册事件后会返回一个SelectionKey对象用以跟踪注册事件句柄
			//该SelectionKey将会放入Selector的all-keys集合中，如果相应的事件触发
			//该SelectionKey将会放入Selector的selected-keys集合中
			serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT);
		}catch(Exception e){
			e.printStackTrace();
			logger.error("Server establish error!");
		}
		logger.info("Server start up!");
	}

	public void service() throws Exception{
		//判断是否有触发事件
		while(selector.select() > 0){
			Set<SelectionKey> selectedKeys = selector.selectedKeys();
			Iterator<SelectionKey> iterator = selectedKeys.iterator();
			
			while(iterator.hasNext()){
				SelectionKey selectionKey = iterator.next();
				//处理事件后将事件从Selector的selected-keys集合中删除
				iterator.remove();
				try{
					if(selectionKey.isAcceptable()){
						this.Acceptable(selectionKey);
					}else if(selectionKey.isReadable()){
						this.Readable(selectionKey);
					}else if(selectionKey.isWritable()){
						this.Writable(selectionKey);
					}
				}catch(Exception e){
					e.printStackTrace();
					logger.error("event deal exception!");
				}
			}
		}
	}
	
	private void Acceptable(SelectionKey selectionKey) throws Exception{
		logger.info("accept:"+(++step));
		
		ServerSocketChannel ssc = (ServerSocketChannel)selectionKey.channel();
		SocketChannel sc = (SocketChannel)ssc.accept();
		
		sc.configureBlocking(false);
		sc.register(selector, SelectionKey.OP_READ);
		
		logger.info(selectionKey.hashCode());
	}
	
	private void Readable(SelectionKey selectionKey) throws Exception{
		logger.info("read:"+(++step));
		
		SocketChannel sc = (SocketChannel)selectionKey.channel();
		
		buffer.clear();
		int num = sc.read(buffer);
		String request = "";
		if(num > 0){
			buffer.flip();
			
			request = charset.decode(buffer).toString();
			sc.register(selector, SelectionKey.OP_WRITE,request);
		}else{
			sc.close();
		}
		
		logger.info(selectionKey.hashCode()+":"+request);
	}
	
	private void Writable(SelectionKey selectionKey) throws Exception{
		logger.info("write:"+(++step));
		
		String request = (String)selectionKey.attachment();
		SocketChannel sc = (SocketChannel)selectionKey.channel();
		
		String answer = "not supported";
		if(request.equals("your name?")){
			answer = "server";
		}
		
		logger.info(selectionKey.hashCode()+":"+answer);
		
		buffer.clear();
		buffer.put(charset.encode(answer));
		buffer.flip();
		while(buffer.hasRemaining())
			sc.write(buffer);
		
		sc.close();
	}
	
	public static void main(String[] args) {
		Server server = new Server();
		try{
			server.service();
		}catch(Exception e){
			e.printStackTrace();
			logger.error("Server run exception!");
		}
	}
}

IO工具类：

package com.test.util;

import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.Socket;

public class SocketIO{
	public static DataInputStream getInput(Socket socket) throws IOException{
		//接收缓存区大小，socket获取输入流之前设置
		socket.setReceiveBufferSize(10);
		InputStream input = socket.getInputStream();
		return new DataInputStream(input);
	}
	
	public static DataOutputStream getOutput(Socket socket) throws IOException{
		//发送缓存区大小，socket获取输出流之前设置
		socket.setSendBufferSize(10);
		OutputStream output = socket.getOutputStream();
		return new DataOutputStream(output);
	}
}

log4j日志配置文件：

log4j.rootLogger=debug,logOutput

log console out put 
log4j.appender.logOutput=org.apache.log4j.ConsoleAppender
log4j.appender.logOutput.layout=org.apache.log4j.PatternLayout
log4j.appender.logOutput.layout.ConversionPattern=%p%d{[yy-MM-dd HH:mm:ss]}[%c] -> %m%n

server端的运行结果：

INFO[13-10-16 11:40:41][com.test.server.Server] -> Server start up!
INFO[13-10-16 11:40:53][com.test.server.Server] -> accept:1
INFO[13-10-16 11:41:14][com.test.server.Server] -> 20469344
INFO[13-10-16 11:41:21][com.test.server.Server] -> read:2
INFO[13-10-16 11:41:37][com.test.server.Server] -> 11688861:your name?
INFO[13-10-16 11:43:00][com.test.server.Server] -> write:3
INFO[13-10-16 11:43:00][com.test.server.Server] -> 11688861:server

可以看到readable方法中的SelectionKey和writable方法中的SelectionKey的哈希码是完全相同的，是同一个SelectionKey

SelectionKey是在SocketChannel类或ServerSocketChannel类注册要监控的事件时产生的，这两个类本身并没有register方法，需要查看它们共同父类AbstractSelectableChannel（只有关键代码）：

public abstract class AbstractSelectableChannel
		extends SelectableChannel{
	......
	// Keys that have been created by registering this channel with selectors.
    // They are saved because if this channel is closed the keys must be
    // deregistered.  Protected by keyLock.
    private SelectionKey[] keys = null;

	public final SelectionKey register(Selector sel, int ops, Object att)
			throws ClosedChannelException{
		if (!isOpen())
			throw new ClosedChannelException();
		if ((ops & ~validOps()) != 0)
			throw new IllegalArgumentException();
		synchronized (regLock) {
			if (blocking)
				throw new IllegalBlockingModeException();
			SelectionKey k = findKey(sel);
			if (k != null) {
				k.interestOps(ops);
				k.attach(att);
			}
			if (k == null) {
				// New registration
				k = ((AbstractSelector)sel).register(this, ops, att);
				addKey(k);
			}
			return k;
		}
	}

	private SelectionKey findKey(Selector sel) {
		synchronized (keyLock) {
			if (keys == null)
	        	return null;
		    for (int i = 0; i < keys.length; i++)
	        	if ((keys[i] != null) && (keys[i].selector() == sel))
	            	return keys[i];
		    return null;
		}
	}

	void removeKey(SelectionKey k) {			// package-private
		synchronized (keyLock) {
		    for (int i = 0; i < keys.length; i++)
			if (keys[i] == k) {
			    keys[i] = null;
			    keyCount--;
			}
		    ((AbstractSelectionKey)k).invalidate();
		}
	}
	......
}

ServerSocketChannel和Socketchannel向Selector中注册了特定事件，Selector就会监控这些事件是否发生。ServerSocketChannel和Socketchannel都为AbstractSelectableChannel类的子类，AbstractSelectableChannel类的register方法负责注册事件，该方法会返回一个SelectionKey对象，该对象用于跟踪被注册事件

public abstract class SelectionKey {
    protected SelectionKey() { }

    public abstract SelectableChannel channel();

    public abstract Selector selector();
    ......
}

一个Selector对象中包含了3种类型的键集（即SelectionKey集合，SelectionKey在以下部分被称为“键”）

1，all-keys:所有注册至该Selector的事件键集（selector.keys()）

2，selected-keys:相关事件已经被Selector捕获的键集（selector.selectedKeys()）

3，cancel-keys:已被取消的键集（无法访问该集合）

selected-keys和cancel-keys都为all-keys的子集，对于一个新建的Selector，这3个键集都为空

注册事件时会将相应的SelectionKey加入Selector的all-keys键集中

取消SelectionKey或者关闭了SelectionKey相关联的Channel，则会将相应的SelectionKey加入cancel-keys键集中

当执行选择器的选择操作时（selector.select()，对于选择器来说，这个方法应该是相当重要的）:

1,将cancel-keys中的每个SelectionKey从3个键集中移除（如果存在的话），并注销SelectionKey所关联的Channel，cancel-keys键集变为空集。

2,如果监控的事件发生，Selector会将相关的SelectionKey加入selected-keys键集中

 

以下为对源代码的分析、推测：

Selector作为选择器，保存了所有的Selectionkey（注册的，取消的，触发的），通过上面的AbstractSelectableChannel类的源代码，发现Channel本身也保存了一个自身关联的SelectionKey数组，这看起来是完全没有必要的，但是仔细看一下register方法，能看出些许端倪：

Selector本身维护了3个集合，all-keys，selected-keys和cancel-keys，频繁的注册操作、取消注册将会导致这3个集合频繁的变化，伴随频繁变化的是频繁的加锁，这会严重的降低Selector的性能，毕竟一个Selector会被多个Channel作为选择器使用，本身非阻塞的实现方式就是提高性能的一种解决方式

当注册新的事件时，如果存在该通道相关的SelectionKey，则更新该SelectionKey所关注的事件以及其携带的附加信息，如果不存在，则添加新的SelectionKey

这样做的好处是，比起删除以前的SelectionKey，添加新的SelectionKey，修改SelectionKey所关注的事件以及其携带的附加信息显然是更好的选择，毕竟不需要修改Selector所维护的键集，当然也不需要频繁加锁（通过查看Selector类的api，SelectionKey并不是thread-safe的，显然并没有加锁，但是并没有什么问题），能够提供更好的性能

 

总之，SelectionKey的哈希码会重复是很正常的，毕竟不是单纯的注册时新建、触发后删除方式，java实现时进行了优化