Netty客户端Handler

在 Netty 配置客户端端时，添加的真正处理业务逻辑的 NettyClientHandler 。

概述

NettyClientHandler 继承 ChannelInboundHandlerAdapter，覆写 channelRead、userEventTriggered、exceptionCaught三个方法。
channelRead ：处理服务端返回的数据，交由 CompletableFuture返回（下一篇会讲到 CompletableFuture）给代理方法。
userEventTriggered：对Netty心跳检测事件进行处理，几秒没有写操作的话，发送一个心跳信息过去，以防止服务端关闭ctx。
exceptionCaught：处理异常。

实现代码

	@Override
	public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        try {
            log.info("client receive msg : [{}]", msg);
            if (msg instanceof RpcResponse) {
                RpcResponse<Object> rpcResponse = (RpcResponse<Object>) msg;
                unprocessedRequests.complete(rpcResponse);
            }
        } finally {
            ReferenceCountUtil.release(msg);
        }
    }

    @Override
    public void userEventTriggered(ChannelHandlerContext ctx, Object evt) throws Exception {
        if (evt instanceof IdleStateEvent) {
            IdleState state = ((IdleStateEvent) evt).state();
            if (state == IdleState.WRITER_IDLE) {
                log.info("write idle happen [{}]", ctx.channel().remoteAddress());
                Channel channel = channelProvider.get((InetSocketAddress) ctx.channel().remoteAddress());
                RpcRequest rpcRequest = RpcRequest.builder().rpcMessageType(RpcMessageType.HEART_BEAT).build();
                channel.writeAndFlush(rpcRequest).addListener(ChannelFutureListener.CLOSE_ON_FAILURE);
            }
        } else {
            super.userEventTriggered(ctx, evt);
        }
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        super.exceptionCaught(ctx, cause);
    }