Session是Apache的核心，每当一个客户端连接到达时，就会有一个新的Session被创建，直到该连接关闭。Session被用来保存连接，以及各种信息。
Session有如下几种状态：
Connected : the session has been created and is availableIdle : the session hasn't processed any request for at least a period of time (this period is configurable)Idle for read : no read has actually been made for a period of timeIdle for write : no write has actually been made for a period of timeIdle for both : no read nor write for a period of timeClosing : the session is being closed (the remaining messages are being flushed, cleaning up is not terminated)Closed : The session is now closed,<div style="color:transparent">！本文来源gaodai.ma#com搞##代!^码网(</div><sup>搞gaodaima代码</sup> nothing else can be done to revive it.
下图表示Session的状态转换关系：
以下几个参数可以用来配置Session
receive buffer size
sending buffer size
Idle time
Write timeOut
管理用户自定义的属性：
例如，如果你想跟踪一个用户从会话被建立之后发送了多少个请求，那么它可以很容易存入这种映射：只要创建一个key关联到value就行。
... int counterValue = session.getAttribute( "counter" ); session.setAttribute( "counter", counterValue + 1 ); ...
我们采用key/value 对的方式存储属性到会话中，这种key/value对可以通过session的容器读取，添加或删除。
定义container
正如我们所说，这个容器是一个key/value容器，默认是一种映射，当然也可以定义成其他的数据结构。当Session被创建时我们可以实现一个接口和一个factory用来创建容器。下面的代码片段示例了在Session初始化时如何创建容器（看不懂，这个到底什么意思？）
protected final void initSession(IoSession session, IoFuture future, IoSessionInitializer sessionInitializer) { ... try { ((AbstractIoSession) session).setAttributeMap(session.getService() .getSessionDataStructureFactory().getAttributeMap(session)); } catch (IoSessionInitializationException e) { throw e; } catch (Exception e) { throw new IoSessionInitializationException( "Failed to initialize an attributeMap.", e); }
and here is the factory interface we can implement if we want to define another kind of container :
public interface IoSessionDataStructureFactory { /** * Returns an {@link IoSessionAttributeMap} which is going to be associated * with the specified <tt>session</tt>. Please note that the returned * implementation must be thread-safe. */ IoSessionAttributeMap getAttributeMap(IoSession session) throws Exception; }
过滤链
每个会话会关联一些过滤链，用来处理到来的请求或者出去的数据。每个会话都会指定单独的过滤链，大多数情况下，我们会用在会话中用很多相同的过滤链。
统计
Each session also keep a track of records about what has been done for the session :number of bytes received/sentnumber of messages received/sentIdle statusthroughputand many other useful informations.Handler
最后，同样重要的是，一个Handler要附着于一个Session上，用来处理程序的消息。这个Handler也会发送包作为回应，只要简单的调用write方法即可：
... session.write( <your message> ); ...
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