java netty之ChannelPipeline

好像在前面的文章中，把netty定义的channel基本上都还算分析了一下吧。。但是channel部分空缺了一个比较重要的东西没有分析，那就是pipeline，所有的操作都是通过pipeline来进行的。。。

还是按照惯例，先来看看ChannelPipeline的继承体系：

这里看到的是三个最顶层的接口，ChannelPipeline同时继承了ChannelInboundInvoker和ChannelOutboundInvoker，

首先我们先来看看ChannelInboundInvoker吧，看这个接口的名字其实基本上就能知道它是干嘛的了，顾名思义就是当channel有数据进来的时候需要用它来处理。。。

//当channel的一些状态发生变化的时候，会调用里面的一些对应的方法interface ChannelInboundInvoker {    /**     * A {@link Channel} was registered to its {@link EventLoop}.     *     * This will result in having the  {@link ChannelStateHandler#channelRegistered(ChannelHandlerContext)} method     * called of the next  {@link ChannelStateHandler} contained in the  {@link ChannelPipeline} of the     * {@link Channel}.     *///当当前的channel注册到eventloop后会调用，最终会调用链表的第一个ChannelStateHandler的channelRegistered函数    ChannelInboundInvoker fireChannelRegistered();    /**     * A {@link Channel} was unregistered from its {@link EventLoop}.     *     * This will result in having the  {@link ChannelStateHandler#channelUnregistered(ChannelHandlerContext)} method     * called of the next  {@link ChannelStateHandler} contained in the  {@link ChannelPipeline} of the     * {@link Channel}.     */    //当所属的channel unregister的时候调用    ChannelInboundInvoker fireChannelUnregistered();    /**     * A {@link Channel} is active now, which means it is connected.     *     * This will result in having the  {@link ChannelStateHandler#channelActive(ChannelHandlerContext)} method     * called of the next  {@link ChannelStateHandler} contained in the  {@link ChannelPipeline} of the     * {@link Channel}.     */    ChannelInboundInvoker fireChannelActive();    /**     * A {@link Channel} is inactive now, which means it is closed.     *     * This will result in having the  {@link ChannelStateHandler#channelInactive(ChannelHandlerContext)} method     * called of the next  {@link ChannelStateHandler} contained in the  {@link ChannelPipeline} of the     * {@link Channel}.     */    ChannelInboundInvoker fireChannelInactive();    /**     * A {@link Channel} received an {@link Throwable} in one of its inbound operations.     *     * This will result in having the  {@link ChannelStateHandler#exceptionCaught(ChannelHandlerContext, Throwable)}     * method  called of the next  {@link ChannelStateHandler} contained in the  {@link ChannelPipeline} of the     * {@link Channel}.     */    ChannelInboundInvoker fireExceptionCaught(Throwable cause);    /**     * A {@link Channel} received an user defined event.     *     * This will result in having the  {@link ChannelStateHandler#userEventTriggered(ChannelHandlerContext, Object)}     * method  called of the next  {@link ChannelStateHandler} contained in the  {@link ChannelPipeline} of the     * {@link Channel}.     */    ChannelInboundInvoker fireUserEventTriggered(Object event);    /**     * A {@link Channel} received bytes which are now ready to read from its inbound buffer.     *     * This will result in having the  {@link ChannelStateHandler#inboundBufferUpdated(ChannelHandlerContext)}     * method  called of the next  {@link ChannelStateHandler} contained in the  {@link ChannelPipeline} of the     * {@link Channel}.     */    //已经有数据到了buffer里面可以读取了，最终会调用inboundBufferUpdated方法，用于处理数据    ChannelInboundInvoker fireInboundBufferUpdated();    /**     * Triggers an {@link ChannelStateHandler#channelReadSuspended(ChannelHandlerContext) channelReadSuspended}     * event to the next {@link ChannelStateHandler} in the {@link ChannelPipeline}.     */    ChannelInboundInvoker fireChannelReadSuspended();}

定义还是很简单，无非都是当channel的状态发生改变的时候，调用channel的stathandler相应的方法。。。这里有一个比较重要的方法：

    //已经有数据到了buffer里面可以读取了，最终会调用inboundBufferUpdated方法，用于处理数据    ChannelInboundInvoker fireInboundBufferUpdated();

它是在当已经有数据读取了，并保存到了buffer之后会调用的方法，用于找到整个handler链的第一个inboundhandler同时也是stathandler的inbountBufferUpdated方法来处理这些数据

接下来来看ChannelOutboundInvoker，顾名思义就是用来处理一些出口数据的，其实也就是一些数据的发送，当然还有connect之类的，这里就不列它的代码了，主要是有一些connect，write，sendfile等方法，其实最终这些都是调用pipeline上的operationhandler来进行具体的操作的。。。。

最后我们来看ChannelPipeline接口的定义，首先它既是inboundinvoker也是outboundinvoker，同时它最终又是一个channelhandler的管理器，在其中的定义的方法主要是对这些handler进行维护的方法，例如：

    //将handler放到最靠前的位置    ChannelPipeline addFirst(String name, ChannelHandler handler);    /**     * Inserts a {@link ChannelHandler} at the first position of this pipeline.     *     * @param group    the {@link EventExecutorGroup} which will be used to execute the {@link ChannelHandler}     *                 methods     * @param name     the name of the handler to insert first     * @param handler  the handler to insert first     *     * @throws IllegalArgumentException     *         if there's an entry with the same name already in the pipeline     * @throws NullPointerException     *         if the specified name or handler is {@code null}     */    //多了一个executor，这里表示handler由这个executor执行    ChannelPipeline addFirst(EventExecutorGroup group, String name, ChannelHandler handler);

每一个channel都会分配一个pipeline对象用于维护当前channel的handler，这些handler又分为两种类型，

（1）inboundhandler，同时也是stathandler，他们主要是在channel的状态发生改变的时候用的，例如当有数据已经读取了，那么会调用相应的方法来处理数据

（2）outboundhandler，同时也是operationhandler，这些handler则是用于具体的数据发送等操作，例如connect，write等。。。。

好了，对pipeline的简单的分析就差不多了。。。可以给它下一个定义：它是数据出入口的处理器，同时还要管理用户定义的handler。。。。