Mina源码分析——IoService

   这两天看了下Mina和Netty的源码，想比较来说Mina的结构简洁易懂。Mina和Netty出自同一人，而Netty是作者对Mina的重构版，改进了很多。如果学习网络编程的话，个人建议从Mina开始，学完Mina后再看Netty，学习曲线会变得很平滑；同时还能深刻理解到作者改进点。

   先看下Mina的结构图，如果之前做过java的web开发，熟悉servlet规范，看到这个结构图，会觉得非常亲切。这个结构描述了基本的网络开发结构。

• IoService  服务端和客户端I/O 操作的抽象，服务端为IoAcceptor，客户端为IoConnector
• IoSession  封装了服务端与客服端连接的会话信息
• IoFilterChain IoFilter处理链
• IoFilter   对服务端和客户端交互的数据做处理
• IoHandler  业务处理

好了，说了那么多还是先分析代码吧。Mina的客户端和服务端开发会略有不同，因为java网络编程的本身就是如此。我们先从分析服务器端开发入手。这里引用了Mina example中的Timer server，它的逻辑非常简单，就是接收到客户端的请求后，返回服务器的当前时间。

TimerServerHandler.java

public class TimeServerHandler extends IoHandlerAdapter {

	@Override
	public void messageReceived(IoSession session, Object message) throws Exception {
		String msg = (String) message;
		if ("quit".equals(msg.trim())) {
			System.out.println("client " + session.getRemoteAddress() + " quited!");
			session.close(false);
			return;
		}

		Date date = new Date();
		session.write(date.toString());
		System.out.println("message written...");
	}

}

开启服务器

private static final int SERVER_PORT = 8888;

public static void main(String[] args) throws IOException {
	IoAcceptor acceptor = new NioSocketAcceptor();

	acceptor.getFilterChain().addLast("logging", new LoggingFilter());
	acceptor.getFilterChain().addLast("codec",
			new ProtocolCodecFilter(new TextLineCodecFactory(Charset.forName("UTF-8"))));

	acceptor.setHandler(new TimeServerHandler());

	acceptor.getSessionConfig().setIdleTime(IdleStatus.BOTH_IDLE, 10);
	acceptor.getSessionConfig().setReadBufferSize(2048);

	acceptor.bind(new InetSocketAddress(SERVER_PORT));
}

1、先创建一个IoAcceptor实例，这里创建的是一个基于tcp的Java NIO版的IoAccptor
2、往FilterChain中追加了 LoggingFilter 和TextLineCodecFactory，LoggingFilter 可以对客户端的请求和服务器端的响应日志记录。TextLineCodecFactory 是一个协议编码解码器的工厂，就是将字节流与java中的String之间的相互转换。后面会详细介绍。
3、添加一个TimerServerHandler实例。TimeServerHandler 处理的逻辑就是在接收到客户端发送过来的字符串信息后，判断如果是quit，关闭与客户端的链接。不是的就返回服务器的当前时间的字符串。
4、设置一些IoSession的可配属性
5、绑定到一个端口上，开始监听客户端的请求。


上面我们只写了一个TimerServerHandler，并在messageReceived 方法中定义了自己的业务处理就轻松的完成了一个服务器端的开发，而不用去关心底层的链接和I/O处理，这就是mina的魅力所在，让开发人员从处理容易出错的I/O操作中解放出来。

现在我们逐个分析代码中出现的一些类和方法。先看一个IoService的继承体系。Mina提供了丰富的实现，支持很多协议，IoService的继承体系没有下面简单。简单起见，上面的图中值画出了Server端的结构，分析IoServeric先从IoAcceptor入手，而且就分析我们熟悉的java nio相关的类。



IoAcceptor是IoService在服务器端的一个抽象。先从接口的功能开始分析：

public interface IoService {

    TransportMetadata getTransportMetadata();

    void addListener(IoServiceListener listener);

    void removeListener(IoServiceListener listener);

    boolean isDisposing();

    boolean isDisposed();

    void dispose();

    void dispose(boolean awaitTermination);

    IoHandler getHandler();

    void setHandler(IoHandler handler);

    Map<Long, IoSession> getManagedSessions();

    int getManagedSessionCount();

    IoSessionConfig getSessionConfig();

    IoFilterChainBuilder getFilterChainBuilder();

    void setFilterChainBuilder(IoFilterChainBuilder builder);

    DefaultIoFilterChainBuilder getFilterChain();

    boolean isActive();

    long getActivationTime();

    Set<WriteFuture> broadcast(Object message);

    IoSessionDataStructureFactory getSessionDataStructureFactory();

    void setSessionDataStructureFactory(IoSessionDataStructureFactory sessionDataStructureFactory);

    int getScheduledWriteBytes();

    int getScheduledWriteMessages();

    IoServiceStatistics getStatistics();
}

从接口的方法上分析可以了解到IoService的主要功能：
1、获取链接通信的元数据
2、IoService维护一个IoServiceListener的列表，IoServiceListener顾名思义，就是对IoService相关的事件进行监听。
3、关闭链接
4、一个IoService对应有一个IoHandler
5、IoService维护这一个IoSession的map
6、一个IoService对应一个FilterChain
7、支持广播功能
8、管理IoSession的中的数据结构
9、统计功能

IoAcceptor    在IoService基础上扩展了绑定和解绑SocketAddress的功能。
SocketAcceptor    在IoAcceptor的基础上将SocketAddress 具体化到InetSocketAddress，同时将IoSessionConfig具体化到SocketSessionConfig。提供了reuseaddress 和backlog的设置。关于backlog在SocketServer中的文档描述是

引用

backlog requested maximum length of the queue of incoming connections.

抽象类分析：
AbstractIoService 提供了IoService中的一些默认实现。

protected AbstractIoService(IoSessionConfig sessionConfig, Executor executor) {
	if (sessionConfig == null) {
		throw new IllegalArgumentException("sessionConfig");
	}

	if (getTransportMetadata() == null) {
		throw new IllegalArgumentException("TransportMetadata");
	}

	if (!getTransportMetadata().getSessionConfigType().isAssignableFrom(
			sessionConfig.getClass())) {
		throw new IllegalArgumentException("sessionConfig type: "
				+ sessionConfig.getClass() + " (expected: "
				+ getTransportMetadata().getSessionConfigType() + ")");
	}

	listeners = new IoServiceListenerSupport(this);
	listeners.add(serviceActivationListener);

	this.sessionConfig = sessionConfig;

	ExceptionMonitor.getInstance();

	if (executor == null) {
		this.executor = Executors.newCachedThreadPool();
		createdExecutor = true;
	} else {
		this.executor = executor;
		createdExecutor = false;
	}

	threadName = getClass().getSimpleName() + '-' + id.incrementAndGet();
}

从AbstractIoService 构造函数来分析可以得知
1、AbstractIoService中只定义了上面的构成函数，没有显式定义无参构造函数，所以在子类的初始化在肯定会调用super(IoSessionConifg,Executor)，再从上面构造函数前面的判断来看，IoSessionConfig,TransportMetadata都是由子类构造函数传入。Executor 参数子类可传可不传，不传默认Executors.newCachedThreadPool();创建。
2、IoServiceListener 列表的管理交给了IoServiceListenerSupport去处理。并添加了一个IoService激活事件的监听器。
3、创建了一个ExceptionMonitor实例
4、定义了构造Acceptor处理线程名称的逻辑

构造函数之外，AbstractIoService 也定义了一些默认实现
1、IoFilterChain 默认交给DefaultIoFilterChainBuilder 创建
2、IoSessionDataStructureFactory 默认实现为 DefaultIoSessionDataStructureFactory
3、实现了dispose的基本逻辑，为什么说是基本逻辑呢？因为dispose调用的 dispose0方法是交由子类去实现的

public final void dispose(boolean awaitTermination) {
  if (disposed) {
	  return;
  }

  synchronized (disposalLock) {
	  if (!disposing) {
		  disposing = true;

		  try {
			  dispose0();
		  } catch (Exception e) {
			  ExceptionMonitor.getInstance().exceptionCaught(e);
		  }
	  }
  }

  if (createdExecutor) {
	  ExecutorService e = (ExecutorService) executor;
	  e.shutdownNow();
	  if (awaitTermination) {

		//Thread.currentThread().setName();

		try {
		  LOGGER.debug("awaitTermination on {} called by thread=[{}]", this, Thread.currentThread().getName());
		  e.awaitTermination(Integer.MAX_VALUE, TimeUnit.SECONDS);
		  LOGGER.debug("awaitTermination on {} finished", this);
		} catch (InterruptedException e1) {
		  LOGGER.warn("awaitTermination on [{}] was interrupted", this);
		  // Restore the interrupted status
		  Thread.currentThread().interrupt();
		}
	  }
  }
  disposed = true;
}

4、实现了broadcast

public final Set<WriteFuture> broadcast(Object message) {
	// Convert to Set.  We do not return a List here because only the
	// direct caller of MessageBroadcaster knows the order of write
	// operations.
	final List<WriteFuture> futures = IoUtil.broadcast(message,
			getManagedSessions().values());
	return new AbstractSet<WriteFuture>() {
		@Override
		public Iterator<WriteFuture> iterator() {
			return futures.iterator();
		}

		@Override
		public int size() {
			return futures.size();
		}
	};
}

AbstractIoAcceptor  继承自AbstractIoService并实现了IoAcceptor接口，主要的实现有：
1、增加一个可配置的SocketAddress 列表 defaultLocalAddresses ，以及这个列表的只读版本
2、增加一个已绑定的SocketAddress 列表
3、增加一个disconnectOnUnbind 配置，指定在Unbind时是否断掉与客户端的链接
4、实现了bind的基本逻辑，更具体的逻辑在bindInternal中交由子类去实现

public final void bind(Iterable<? extends SocketAddress> localAddresses) throws IOException {
	if (isDisposing()) {
		throw new IllegalStateException("Already disposed.");
	}
	
	if (localAddresses == null) {
		throw new IllegalArgumentException("localAddresses");
	}
	
	List<SocketAddress> localAddressesCopy = new ArrayList<SocketAddress>();
	
	for (SocketAddress a: localAddresses) {
		checkAddressType(a);
		localAddressesCopy.add(a);
	}
	
	if (localAddressesCopy.isEmpty()) {
		throw new IllegalArgumentException("localAddresses is empty.");
	}
	
	boolean activate = false;
	synchronized (bindLock) {
		synchronized (boundAddresses) {
			if (boundAddresses.isEmpty()) {
				activate = true;
			}
		}

		if (getHandler() == null) {
			throw new IllegalStateException("handler is not set.");
		}
		
		try {
			Set<SocketAddress> addresses = bindInternal( localAddressesCopy );
			
			synchronized (boundAddresses) {
				boundAddresses.addAll(addresses);
			}
		} catch (IOException e) {
			throw e;
		} catch (RuntimeException e) {
			throw e;
		} catch (Throwable e) {
			throw new RuntimeIoException(
					"Failed to bind to: " + getLocalAddresses(), e);
		}
	}
	
	if (activate) {
		getListeners().fireServiceActivated();
	}
}

5、实现了unbind的基本逻辑，更具体的逻辑在unbind0中交由子类实现

public final void unbind(Iterable<? extends SocketAddress> localAddresses) {
	if (localAddresses == null) {
		throw new IllegalArgumentException("localAddresses");
	}
	
	boolean deactivate = false;
	synchronized (bindLock) {
		synchronized (boundAddresses) {
			if (boundAddresses.isEmpty()) {
				return;
			}

			List<SocketAddress> localAddressesCopy = new ArrayList<SocketAddress>();
			int specifiedAddressCount = 0;
			
			for (SocketAddress a: localAddresses ) {
				specifiedAddressCount++;

				if ((a != null) && boundAddresses.contains(a) ) {
					localAddressesCopy.add(a);
				}
			}
			
			if (specifiedAddressCount == 0) {
				throw new IllegalArgumentException( "localAddresses is empty." );
			}
			
			if (!localAddressesCopy.isEmpty()) {
				try {
					unbind0(localAddressesCopy);
				} catch (RuntimeException e) {
					throw e;
				} catch (Throwable e) {
					throw new RuntimeIoException(
							"Failed to unbind from: " + getLocalAddresses(), e );
				}

				boundAddresses.removeAll(localAddressesCopy);
				
				if (boundAddresses.isEmpty()) {
					deactivate = true;
				}
			}
		}
	}

	if (deactivate) {
		getListeners().fireServiceDeactivated();
	}
}

AbstractPollingIoAcceptor<T extends AbstractIoSession, H>
泛参H在子类NioSocketAcceptor中替换为ServerSocketChannel，泛参T替换为NioSession。这样便于分析后面的代码。
主要实现了bind,accept,dispose ServerSocket的基本逻辑。父类AbstractIoService中的Executor主要用于执行ServerSocket的accept逻辑。一旦与客户端建立连接后，之后的I/O操作将交由IoProcessor去处理。关于ServerSocketChannel 的 select,open,close,accept都交由子类实现

私有构造函数定义了IoProcessor实例由外部注入，并初始化seelectable标记为true。具体的init()逻辑由子类去实现。

private AbstractPollingIoAcceptor(IoSessionConfig sessionConfig,
		Executor executor, IoProcessor<NioSession> processor,
		boolean createdProcessor) {
	super(sessionConfig, executor);

	if (processor == null) {
		throw new IllegalArgumentException("processor");
	}
	//注入IoProcessor对象
	this.processor = processor;
	this.createdProcessor = createdProcessor;

	try {
		//初始化设置交给子类实现
		init();
		// 构造函数中设置标记为true，后面便可以s
		selectable = true;
	} catch (RuntimeException e) {
		throw e;
	} catch (Exception e) {
		throw new RuntimeIoException("Failed to initialize.", e);
	} finally {
		if (!selectable) {
			try {
				destroy();
			} catch (Exception e) {
				ExceptionMonitor.getInstance().exceptionCaught(e);
			}
		}
	}
}

其他几个重载的构造函数注入默认IoProcessor为SimpleIoProcessorPool实例

protected AbstractPollingIoAcceptor(IoSessionConfig sessionConfig,
		Class<? extends IoProcessor<T>> processorClass, int processorCount) {
	this(sessionConfig, null, new SimpleIoProcessorPool<T>(processorClass,
			processorCount), true);
}

提供了一个轮询策略的Acceptor的实现

private class Acceptor implements Runnable {
	public void run() {
		// nHandles 表示已经open的ServerSocketChannel数量
		int nHandles = 0;
		//无限循环，接收客户端的链接请求，并处理，直到所有opened ServerSocketChannel都被close
		while (selectable) {
			try {
				//轮询获得
				int selected = select();
				//open ServerSocketChannel并增加nHandles
				nHandles += registerHandles();

				if (selected > 0) {
					// We have some connection request, let's process 
					// them here. 
					processHandles(selectedHandles());
				}

				//close ServerSocketChannel并减少nHandles
				nHandles -= unregisterHandles();
				//没有ServerSocketChannel在监听客户端的请求，跳出循环
				if (nHandles == 0) {
					synchronized (lock) {
						if (registerQueue.isEmpty()
								&& cancelQueue.isEmpty()) {
							acceptor = null;
							break;
						}
					}
				}
			} catch (ClosedSelectorException cse) {
				break;
			} catch (Throwable e) {
				ExceptionMonitor.getInstance().exceptionCaught(e);

				try {
					Thread.sleep(1000);
				} catch (InterruptedException e1) {
					ExceptionMonitor.getInstance().exceptionCaught(e1);
				}
			}
		}

		if (selectable && isDisposing()) {
			selectable = false;
			try {
				if (createdProcessor) {
					processor.dispose();
				}
			} finally {
				try {
					synchronized (disposalLock) {
						if (isDisposing()) {
							destroy();
						}
					}
				} catch (Exception e) {
					ExceptionMonitor.getInstance().exceptionCaught(e);
				} finally {
					disposalFuture.setDone();
				}
			}
		}
	}

	private void processHandles(Iterator<ServerSocketChannel> handles) throws Exception {
		while (handles.hasNext()) {
			ServerSocketChannel handle = handles.next();
			handles.remove();
			// 接收客户端的请求，建立链接，返回对链接信息封装后的IoSession
			NioSession session = accept(processor, handle);
			
			if (session == null) {
				break;
			}
			// 初始化IoSession信息
			initSession(session, null, null);
			// 将连接的I/O(read,write,close etc)交给Processor线程处理
			session.getProcessor().add(session);
		}
	}
}

private int registerHandles() {
	//开启一个无限循环，不断从registerQueue队列中获取AcceptorOperationFuture，直到registerQueue为空
	for (;;) {
		AcceptorOperationFuture future = registerQueue.poll();
		
		if (future == null) {
			return 0;
		}

		// 创建一个临时的map以便在打开socket的时候出现异常及时释放资源
		Map<SocketAddress, ServerSocketChannel> newHandles = new ConcurrentHashMap<SocketAddress, ServerSocketChannel>();
		List<SocketAddress> localAddresses = future.getLocalAddresses();

		try {
			for (SocketAddress a : localAddresses) {
				//遍历所有的SocketAddress，open ServerSocketChannel
				ServerSocketChannel handle = open(a);
				newHandles.put(localAddress(handle), handle);
			}
			// 未出现异常，将所有open成功的ServerSocketChannel放到boundHandles
			boundHandles.putAll(newHandles);
			// 设置异步处理完成
			future.setDone();
			// 返回open成功的ServerSocketChannel的数量
			return newHandles.size();
		} catch (Exception e) {
			future.setException(e);
		} finally {
			//在open时出现了异常，释放相应的 资源
			if (future.getException() != null) {
				for (ServerSocketChannel handle : newHandles.values()) {
					try {
						close(handle);
					} catch (Exception e) {
						ExceptionMonitor.getInstance().exceptionCaught(e);
					}
				}
				
				wakeup();
			}
		}
	}
}

// 关闭ServerSocketChannel
private int unregisterHandles() {
	int cancelledHandles = 0;
	// 循环从cancelQueue队列中获取待关闭的ServerSocketChannel，直到cancelQueue清空
	for (;;) {
		AcceptorOperationFuture future = cancelQueue.poll();
		if (future == null) {
			break;
		}

		for (SocketAddress a : future.getLocalAddresses()) {
			// 先从已绑定的ServerSocketChannel列表中移除
			ServerSocketChannel handle = boundHandles.remove(a);
			
			if (handle == null) {
				continue;
			}

			try {
				//关闭ServerSocketChannel，真正的实现交给子类
				close(handle);
				wakeup();
			} catch (Throwable e) {
				ExceptionMonitor.getInstance().exceptionCaught(e);
			} finally {
				cancelledHandles++;
			}
		}
		//
		future.setDone();
	}
	//返回已关闭的ServerSocketChannel的数量 
	return cancelledHandles;
}

NioSocketAcceptor
基于tcp协议的java nio版IoAcceptor实现，到这里已经实现所有的网络I/O操作。

//默认的ServerSocket的backlog属性为50
private int backlog = 50;
// 默认reuseAddress为false
private boolean reuseAddress = false;
// java nio 中的selector，状态改变多线程可见
private volatile Selector selector;

//构造函数出入的默认IoSessionConfig实现为DefaultSocketSessionConfig
public NioSocketAcceptor() {
	super(new DefaultSocketSessionConfig(), NioProcessor.class);
	((DefaultSocketSessionConfig) getSessionConfig()).init(this);
}
// 如果你熟悉java nio，看到这些代码是否有种豁然开朗的感觉呢？原来是这样的啊！
@Override
protected void init() throws Exception {
	selector = Selector.open();
}

@Override
protected void destroy() throws Exception {
	if (selector != null) {
		selector.close();
	}
}

public TransportMetadata getTransportMetadata() {
	return NioSocketSession.METADATA;
}

@Override
protected NioSession accept(IoProcessor<NioSession> processor,
		ServerSocketChannel handle) throws Exception {

	SelectionKey key = handle.keyFor(selector);
	
	if ((key == null) || (!key.isValid()) || (!key.isAcceptable()) ) {
		return null;
	}

	SocketChannel ch = handle.accept();
	
	if (ch == null) {
		return null;
	}

	return new NioSocketSession(this, processor, ch);
}

@Override
protected ServerSocketChannel open(SocketAddress localAddress)
		throws Exception {
	// Creates the listening ServerSocket
	ServerSocketChannel channel = ServerSocketChannel.open();
	
	boolean success = false;
	
	try {
		// This is a non blocking socket channel
		channel.configureBlocking(false);
	
		// Configure the server socket,
		ServerSocket socket = channel.socket();
		
		// Set the reuseAddress flag accordingly with the setting
		socket.setReuseAddress(isReuseAddress());
		
		// and bind.
		socket.bind(localAddress, getBacklog());
		
		// Register the channel within the selector for ACCEPT event
		channel.register(selector, SelectionKey.OP_ACCEPT);
		success = true;
	} finally {
		if (!success) {
			close(channel);
		}
	}
	return channel;
}

@Override
protected void close(ServerSocketChannel handle) throws Exception {
	SelectionKey key = handle.keyFor(selector);
	
	if (key != null) {
		key.cancel();
	}
	
	handle.close();
}

@Override
protected void wakeup() {
	selector.wakeup();
}