DefaultChannelPipeline

ChannelInitializer

protected abstract void initChannel(C ch) throws Exception;

public final void channelRegistered(ChannelHandlerContext ctx) throws Exception {
        // Normally this method will never be called as handlerAdded(...) should call initChannel(...) and remove
        // the handler.
        if (initChannel(ctx)) {
            // we called initChannel(...) so we need to call now pipeline.fireChannelRegistered() to ensure we not
            // miss an event.
            ctx.pipeline().fireChannelRegistered();

            // We are done with init the Channel, removing all the state for the Channel now.
            removeState(ctx);
        } else {
            // Called initChannel(...) before which is the expected behavior, so just forward the event.
            ctx.fireChannelRegistered();
        }
    }

DefaultChannelHandlerContext

final class DefaultChannelHandlerContext extends AbstractChannelHandlerContext {

    private final ChannelHandler handler;
    ..........................

    @Override
    public ChannelHandler handler() {
        return handler; // 比如addLast(ctx) 这里的handler就是这个ctx
    }
}

DefaultChannelPipeline

构造函数

protected DefaultChannelPipeline(Channel channel) {
        ...........................
        
        tail = new TailContext(this); 
        head = new HeadContext(this);

        head.next = tail;
        tail.prev = head;
    }

    public final ChannelPipeline addLast(ChannelHandler... handlers) {
        return addLast(null, handlers);
    }

public final ChannelPipeline addLast(EventExecutorGroup executor, ChannelHandler... handlers) {
        if (handlers == null) {
            throw new NullPointerException("handlers");
        }

        for (ChannelHandler h: handlers) {
            if (h == null) {
                break;
            }
            addLast(executor, null, h);
        }

        return this;
    }

public final ChannelPipeline addLast(EventExecutorGroup group, String name, ChannelHandler handler) {
        final AbstractChannelHandlerContext newCtx;
        synchronized (this) {
            checkMultiplicity(handler);

            newCtx = newContext(group, filterName(name, handler), handler); 
            // DefaultChannelHandlerContext

            addLast0(newCtx);

            // If the registered is false it means that the channel was not registered on an eventLoop yet.
            // In this case we add the context to the pipeline and add a task that will call
            // ChannelHandler.handlerAdded(...) once the channel is registered.
            if (!registered) {
                newCtx.setAddPending();
                callHandlerCallbackLater(newCtx, true);
                return this;
            }

            EventExecutor executor = newCtx.executor();
            if (!executor.inEventLoop()) {
                callHandlerAddedInEventLoop(newCtx, executor);
                return this;
            }
        }
        callHandlerAdded0(newCtx);
        return this;
    }

newContext

final class DefaultChannelHandlerContext extends AbstractChannelHandlerContext { }

private AbstractChannelHandlerContext newContext(EventExecutorGroup group, String name, ChannelHandler handler) {
        return new DefaultChannelHandlerContext(this, childExecutor(group), name, handler);
    }

addLast0

添加到倒数第2个，最后1个是tail

private void addLast0(AbstractChannelHandlerContext newCtx) {
        AbstractChannelHandlerContext prev = tail.prev;
        newCtx.prev = prev;
        newCtx.next = tail;
        prev.next = newCtx;
        tail.prev = newCtx;
    }