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 available Idle : 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 time Idle for write : no write has actually been made for a period of time Idle for both : no read nor write for a period of time Closing : the session is being closed (the remaining messages are being flushed, cleaning up is not terminated) Closed : The session is now closed, 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 session. 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/sent number of messages received/sent Idle status throughput and 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(); ...
以上就是Apache Mina 学习笔记(4)-Session的内容，更多相关内容请关注PHP中文网（www.php.cn）！
