Mina IoHandler接口定义

Mina 过滤链抽象实现：http://donald-draper.iteye.com/blog/2376335
在上面这篇文章中，当IOService接收消息后，消息被过滤链上的过滤器过滤，从链头到链尾，过程如下：
//消息接收，从链头到链尾-》Iohanlder（这个过程handler处理相关事件）

public void fireMessageReceived(IoSession session, Object message) {
        Entry head = this.head;
        callNextMessageReceived(head, session, message);
}
private void callNextMessageReceived(Entry entry, IoSession session,
            Object message) {
        try {
            entry.getFilter().messageReceived(entry.getNextFilter(), session,
                    message);
        } catch (Throwable e) {
            fireExceptionCaught(session, e);
        }
}

 private static class TailFilter extends IoFilterAdapter {
   private static class TailFilter extends IoFilterAdapter {
       ...
        public void messageReceived(NextFilter nextFilter, IoSession session,
                Object message) throws Exception {
            try {
                session.getHandler().messageReceived(session, message);
            } finally {
	        //如果发送消息对象为ByteBuffer，则释放buffer
                ByteBufferUtil.releaseIfPossible(message);
            }
        }
        ...
}
}

从上可以看出IoService接收消息后，消息过滤链中的过滤器（协议解码器等）过滤后，最后交给会话handler处理，即IoHandler，今天我们来看一下IoHandler。

/**
 * Handles all I/O events fired by MINA.
 * 
 * @author The Apache MINA Project ([e-mail])
 * @version $Rev$, $Date$
 * 
 * @see IoHandlerAdapter
 */
public interface IoHandler {
    /**
     * Invoked from an I/O processor thread when a new connection has been created.
     * Because this method is supposed to be called from the same thread that
     * handles I/O of multiple sessions, please implement this method to perform
     * tasks that consumes minimal amount of time such as socket parameter
     * and user-defined session attribute initialization.
     当一个新的连接创建时，有IO处理器线程调用此方法。由于此方法可以被相同的线程调用，
     处理多个会话IO，所以实现此方法时，执行任务时，尽量消耗尽少的时间，比如做一些Socket参数配置，
     用户自定义的会话属性
     */
    void sessionCreated(IoSession session) throws Exception;

    /**
     * Invoked when a connection has been opened.  This method is invoked after
     * {@link #sessionCreated(IoSession)}.  The biggest difference from
     * {@link #sessionCreated(IoSession)} is that it's invoked from other thread
     * than an I/O processor thread once thread modesl is configured properly.
     当一个连接打开时调用此方法。此方法在会话创建后调用。与会话创建方法不同的是，
     一旦线程模型配置，会话打开被其他线程调用，而不是IO处理器。
     */
    void sessionOpened(IoSession session) throws Exception;

    /**
     * Invoked when a connection is closed.当连接关闭时，调用。
     */
    void sessionClosed(IoSession session) throws Exception;

    /**
     * Invoked with the related {@link IdleStatus} when a connection becomes idle.
     * This method is not invoked if the transport type is UDP; it's a known bug,
     * and will be fixed in 2.0.
     当连接空闲时，sessionIdle方法被相关空闲状态调用。如果传输接口为UDP，此方法不会调用，
     这是一个已知的bug，在2.0版本修复
     */
    void sessionIdle(IoSession session, IdleStatus status) throws Exception;

    /**
     * Invoked when any exception is thrown by user {@link IoHandler}
     * implementation or by MINA.  If <code>cause</code> is instanceof
     * {@link IOException}, MINA will close the connection automatically.
     当用户的IO处理器抛出异常时，方法有mina调用。如果异常为IOException,mina将
     自动关闭连接。
     */
    void exceptionCaught(IoSession session, Throwable cause) throws Exception;

    /**
     * Invoked when a message is received.接收消息时，调用
     */
    void messageReceived(IoSession session, Object message) throws Exception;

    /**
     * Invoked when a message written by {@link IoSession#write(Object)} is
     * sent out.
     当消息被Io会话write方法发送出去后，调用
     */
    void messageSent(IoSession session, Object message) throws Exception;
}

//IoHandlerAdapter

/**
 * An abstract adapter class for {@link IoHandler}.  You can extend this
 * class and selectively override required event handler methods only.  All
 * methods do nothing by default. 
 * IoHandlerAdapter为IO处理器的简单实现。你可以扩展此类或重写需要关注的事件处理方法，
 默认所有方法什么都不做。
 * @author The Apache Directory Project ([e-mail])
 * @version $Rev$, $Date$
 */
public class IoHandlerAdapter implements IoHandler {
    public void sessionCreated(IoSession session) throws Exception {
        SessionUtil.initialize(session);
    }
    public void sessionOpened(IoSession session) throws Exception {
    }

    public void sessionClosed(IoSession session) throws Exception {
    }
    public void sessionIdle(IoSession session, IdleStatus status)
            throws Exception {
    }
    public void exceptionCaught(IoSession session, Throwable cause)
            throws Exception {
        if (SessionLog.isWarnEnabled(session)) {
            SessionLog.warn(session, "EXCEPTION, please implement "
                    + getClass().getName()
                    + ".exceptionCaught() for proper handling:", cause);
        }
    }
    public void messageReceived(IoSession session, Object message)
            throws Exception {
    }
    public void messageSent(IoSession session, Object message) throws Exception {
    }
}