netty源码解析(二)read write

当创建NioEventLoop的时候，可以使用addLast方法添加Handler,如果是ChannelInboundHandler类型，则在读取数据的时候，会调用其read方法，如果是ChannelOutboundHandler类型，则会在写出数据的时候，调用其write()方法

 

当netty在读写数据的时候，会调用DefaultChannelPipeline的read()和write()方法，在DefaultChannelPipeline中，初始化的时候创建了一个TailContext和一个HeadContext，分别作为读取和写数据的第一个Handler:

    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;
    }

read

当调用read()方法的时候，是从HeadContext开始，从TailContext结束

    @Override
    public final ChannelPipeline fireChannelRead(Object msg) {
        AbstractChannelHandlerContext.invokeChannelRead(head, msg);
        return this;
    }

    @Override
    public final ChannelPipeline fireChannelRead(Object msg) {
        AbstractChannelHandlerContext.invokeChannelRead(head, msg);
        return this;
    }

write

当write写数据的时候，从TailContext开始，从HeadContext结束

    @Override
    public final ChannelFuture write(Object msg) {
        return tail.write(msg);
    }

    @Override
    public final ChannelFuture write(Object msg, ChannelPromise promise) {
        return tail.write(msg, promise);
    }

    @Override
    public final ChannelFuture writeAndFlush(Object msg, ChannelPromise promise) {
        return tail.writeAndFlush(msg, promise);
    }

    @Override
    public final ChannelFuture writeAndFlush(Object msg) {
        return tail.writeAndFlush(msg);
    }

 

        @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();
        }