@Overridepublic ChannelFuture writeAndFlush(Object msg, ChannelPromise promise) {DefaultChannelHandlerContext next;next = findContextOutbound(MASK_WRITE);ReferenceCountUtil.touch(msg, next);next.invoker.invokeWrite(next, msg, promise);next = findContextOutbound(MASK_FLUSH);next.invoker.invokeFlush(next);return promise;}

        @Overridepublic void write(Object msg, ChannelPromise promise) {ChannelOutboundBuffer outboundBuffer = this.outboundBuffer;if (outboundBuffer == null) {// If the outboundBuffer is null we know the channel was closed and so// need to fail the future right away. If it is not null the handling of the rest// will be done in flush0()// See https://github.com/netty/netty/issues/2362
                safeSetFailure(promise, CLOSED_CHANNEL_EXCEPTION);// release message now to prevent resource-leak
                ReferenceCountUtil.release(msg);return;}outboundBuffer.addMessage(msg, promise);}

 @Overrideprotected void doWrite(ChannelOutboundBuffer in) throws Exception {int writeSpinCount = -1;for (;;) {Object msg = in.current();if (msg == null) {// Wrote all messages.
                clearOpWrite();break;}if (msg instanceof ByteBuf) {ByteBuf buf = (ByteBuf) msg;int readableBytes = buf.readableBytes();if (readableBytes == 0) {in.remove();continue;}boolean setOpWrite = false;boolean done = false;long flushedAmount = 0;if (writeSpinCount == -1) {writeSpinCount = config().getWriteSpinCount();}for (int i = writeSpinCount - 1; i >= 0; i --) {int localFlushedAmount = doWriteBytes(buf); // 这里才是实际将数据写出去的地方if (localFlushedAmount == 0) {setOpWrite = true;break;}flushedAmount += localFlushedAmount;if (!buf.isReadable()) {done = true;break;}}in.progress(flushedAmount);if (done) {in.remove();} else {incompleteWrite(setOpWrite);break;}} else if (msg instanceof FileRegion) {FileRegion region = (FileRegion) msg;boolean setOpWrite = false;boolean done = false;long flushedAmount = 0;if (writeSpinCount == -1) {writeSpinCount = config().getWriteSpinCount();}for (int i = writeSpinCount - 1; i >= 0; i --) {long localFlushedAmount = doWriteFileRegion(region);if (localFlushedAmount == 0) {setOpWrite = true;break;}flushedAmount += localFlushedAmount;if (region.transfered() >= region.count()) {done = true;break;}}in.progress(flushedAmount);if (done) {in.remove(); // 根据写出的数据的数量情况, 来判断操作是否完成, 如果完成则调用 in.remove()} else {incompleteWrite(setOpWrite);break;}} else {throw new UnsupportedOperationException("unsupported message type: " + StringUtil.simpleClassName(msg));}}}

    public final boolean remove() {if (isEmpty()) {return false;}Entry e = buffer[flushed];Object msg = e.msg;if (msg == null) {return false;}ChannelPromise promise = e.promise;int size = e.pendingSize;e.clear();flushed = flushed + 1 & buffer.length - 1;if (!e.cancelled) {// only release message, notify and decrement if it was not canceled before.
            safeRelease(msg);safeSuccess(promise); // 这里, 调用了promise的trySuccess()方法, 触发ListenerdecrementPendingOutboundBytes(size);}return true;}

@Overridepublic void channelRead(ChannelHandlerContext ctx, Object msg) {ctx.writeAndFlush(new Object()).addListener(new ChannelFutureListener() {@Overridepublic void operationComplete(ChannelFuture future) throws Exception {if (future.isSuccess()) {// do sth} else {// do sth
                }}});}

selectionKey = javaChannel().register(eventLoop().selector, 0, this);