netty：不同顺序InBoundHandler之间的数据传递

pipeline

// out handler
socketChannel.pipeline().addLast(new StringEncoder());
// in handler
socketChannel.pipeline().addLast(new StringDecoder());
socketChannel.pipeline().addLast(new MyServerChannelInBoundHandler1());
socketChannel.pipeline().addLast(new MyServerChannelInBoundHandler2());

注意【MyServerChannelInBoundHandler1】必须在【MyServerChannelInBoundHandler2】的上面
【MyServerChannelInBoundHandler1.java】

@Slf4j
public class MyServerChannelInBoundHandler1 extends SimpleChannelInboundHandler<String>
{
    @Override
    protected void channelRead0(ChannelHandlerContext ctx, String msg) throws Exception {
        log.info("MyServerChannelInBoundHandler1.channelRead0[" + ctx.channel().remoteAddress() + "]:" + msg);
        String retMsg = String.format("server have received data from you:[%s]", msg.trim());
        ctx.writeAndFlush(retMsg);      // 发送数据出去
        ctx.fireChannelRead(retMsg);    // 这一句会触发下一个InBoundHandler的【channelRead】和【channelRead0】被触发
    }
}

注意上面调用了【writeAndFlush(retMsg)】
注意上面调用【fireChannelRead(retMsg)】时参数是被修改过的【retMsg】，而不是【msg】。
【MyServerChannelInBoundHandler2.java】

@Slf4j
public class MyServerChannelInBoundHandler2 extends SimpleChannelInboundHandler<String>
{
    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        log.info("MyServerChannelInBoundHandler2.channelRead[" + ctx.channel().remoteAddress() + "]:" + msg);
        super.channelRead(ctx, msg);
    }

    @Override
    protected void channelRead0(ChannelHandlerContext ctx, String msg) {
        log.info("MyServerChannelInBoundHandler2.channelRead0[" + ctx.channel().remoteAddress() + "]:" + msg);
        ctx.writeAndFlush(msg);        // 发送数据出去，这里的msg是被上面的InBoundHandler修改过的
    }
}

注意【ctx.writeAndFlush()】方法被调用了两次，所以数据其实是被发送了两次出去。
在正常使用中，如果一个InBoundHandler确定了数据是要传给下一个InBoundHandler的话，本handler是不会发送数据的，而是会将数据交给下一个handler去处理，发送数据也由下一个handler发送。