ChannelPipeline 负责channel数据进出处理，如数据编解码等。采用拦截思想设计，经过A handler处理后接着交给next handler
ChannelPipeline 并不是直接管理handler 而是通过 context 包装管理，一般以context 命名的是个重量级对象，提供给多层使用
public interface ChannelPipeline extends ChannelInboundInvoker, ChannelOutboundInvoker, Iterable<Entry<String, ChannelHandler>> { //链表追加handler方法 ChannelPipeline addLast(String name, ChannelHandler handler); ChannelPipeline addLast(EventExecutorGroup group, String name, ChannelHandler handler); ///////////////公开获取 ChannelHandler ChannelHandlerContext///////////////// ChannelHandler first(); ChannelHandlerContext firstContext(); ChannelHandler last(); ChannelHandlerContext lastContext(); //省略部份代码..... ////////////////ChannelInboundInvoker接口的所有方法 统一返回 ChannelPipeline 对象////////////////////// ChannelPipeline fireChannelRegistered(); ChannelPipeline fireChannelUnregistered(); ChannelPipeline fireChannelActive(); ChannelPipeline fireChannelInactive(); ChannelPipeline fireExceptionCaught(Throwable cause); ChannelPipeline fireUserEventTriggered(Object event); ChannelPipeline fireChannelRead(Object msg); ChannelPipeline fireChannelReadComplete(); ChannelPipeline fireChannelWritabilityChanged(); ChannelPipeline flush(); ////////////////ChannelOutboundInvoker接口的所有方法 统一返回 ChannelFuture ChannelOutboundInvoker 对象////////////////////// ChannelFuture bind(SocketAddress localAddress); ChannelFuture connect(SocketAddress remoteAddress); ChannelFuture connect(SocketAddress remoteAddress, SocketAddress localAddress); ChannelFuture disconnect(); ChannelFuture close(); ChannelFuture deregister(); ChannelFuture bind(SocketAddress localAddress, ChannelPromise promise); ChannelFuture connect(SocketAddress remoteAddress, ChannelPromise promise); ChannelFuture connect(SocketAddress remoteAddress, SocketAddress localAddress, ChannelPromise promise); ChannelFuture disconnect(ChannelPromise promise); ChannelFuture close(ChannelPromise promise); ChannelFuture deregister(ChannelPromise promise); ChannelOutboundInvoker read(); ChannelFuture write(Object msg); ChannelFuture write(Object msg, ChannelPromise promise); ChannelOutboundInvoker flush(); ChannelFuture writeAndFlush(Object msg, ChannelPromise promise); ChannelFuture writeAndFlush(Object msg); ChannelPromise newPromise(); ChannelProgressivePromise newProgressivePromise(); ChannelFuture newSucceededFuture(); ChannelFuture newFailedFuture(Throwable cause); ChannelPromise voidPromise(); }
DefaultChannelPipeline实现做了代码整理，其中在添加handler时生成context由于代码比较简单不显示出来
public class DefaultChannelPipeline implements ChannelPipeline { final AbstractChannelHandlerContext head; final AbstractChannelHandlerContext tail; //绑定返回对象 private final Channel channel; private final ChannelFuture succeededFuture; private final VoidChannelPromise voidPromise; protected DefaultChannelPipeline(Channel channel) { this.channel = ObjectUtil.checkNotNull(channel, "channel"); succeededFuture = new SucceededChannelFuture(channel, null); voidPromise = new VoidChannelPromise(channel, true); tail = new TailContext(this); head = new HeadContext(this); head.next = tail; tail.prev = head; } //双向链表追加，在tail之前插入 private void addLast0(AbstractChannelHandlerContext newCtx) { AbstractChannelHandlerContext prev = tail.prev; newCtx.prev = prev; newCtx.next = tail; prev.next = newCtx; tail.prev = newCtx; } //双向链表删除 private static void remove0(AbstractChannelHandlerContext ctx) { AbstractChannelHandlerContext prev = ctx.prev; AbstractChannelHandlerContext next = ctx.next; prev.next = next; next.prev = prev; } //HeadContext ChannelOutboundHandler出站操作通过Unsafe委托处理 final class HeadContext extends AbstractChannelHandlerContext implements ChannelOutboundHandler, ChannelInboundHandler { private final Unsafe unsafe; HeadContext(DefaultChannelPipeline pipeline) { super(pipeline, null, HEAD_NAME, false, true); unsafe = pipeline.channel().unsafe(); setAddComplete(); } @Override public void bind( ChannelHandlerContext ctx, SocketAddress localAddress, ChannelPromise promise) throws Exception { unsafe.bind(localAddress, promise); } @Override public void connect( ChannelHandlerContext ctx, SocketAddress remoteAddress, SocketAddress localAddress, ChannelPromise promise) throws Exception { unsafe.connect(remoteAddress, localAddress, promise); } @Override public void write(ChannelHandlerContext ctx, Object msg, ChannelPromise promise) throws Exception { unsafe.write(msg, promise); } @Override public void flush(ChannelHandlerContext ctx) throws Exception { unsafe.flush(); } @Override public void channelRegistered(ChannelHandlerContext ctx) throws Exception { invokeHandlerAddedIfNeeded(); ctx.fireChannelRegistered(); } @Override public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception { ctx.fireChannelRead(msg); } //...... } } //ChannelHandlerContext 部份代码 //通过findContextInbound 查找下一个ctx 再通过ctx内部调用handler方法 @Override public ChannelHandlerContext fireChannelRegistered() { invokeChannelRegistered(findContextInbound()); return this; } static void invokeChannelRegistered(final AbstractChannelHandlerContext next) { EventExecutor executor = next.executor(); if (executor.inEventLoop()) { next.invokeChannelRegistered(); } else { executor.execute(new Runnable() { @Override public void run() { next.invokeChannelRegistered(); } }); } } private void invokeChannelRegistered() { if (invokeHandler()) { try { ((ChannelInboundHandler) handler()).channelRegistered(this); } catch (Throwable t) { notifyHandlerException(t); } } else { fireChannelRegistered(); } } //数据入站时从头到尾查找ctx private AbstractChannelHandlerContext findContextInbound() { AbstractChannelHandlerContext ctx = this; do { ctx = ctx.next; } while (!ctx.inbound); return ctx; } //数据出站时从尾到头查找ctx private AbstractChannelHandlerContext findContextOutbound() { AbstractChannelHandlerContext ctx = this; do { ctx = ctx.prev; } while (!ctx.outbound); return ctx; }
小总：
1.从设计上可以看出，统一返回一个对象能减少大量的学习成本同开发成本
2.追加handler可以绑定一个线程组，在处理比较耗时的handler可以独立绑定线程组
3.从源码上看出：数据入站时如 channelRead(ChannelHandlerContext ctx, Object msg) 当处理完数据要手动执行next ctx action ctx.fireChannelRead(msg) 这点是比如奇怪的，如果开发者忘记调用了链表就断啦
4.DefaultChannelPipeline构造时默认生成head、tail,数据出站时操作顺序是tail ->linkHandler-> head,数据入站时是 head->linkHandler->tail
5.ChannelPipeline用到双向链表技术，大家在研发过程中可参考设计
