@Override
    public void handlerAdded(ChannelHandlerContext ctx) throws Exception {
        ctx.pipeline()
            .addBefore(ctx.name(), null, new Http2ServerUpgradeHandler.PriorKnowledgeHandler())
            .addBefore(ctx.name(), "HttpServerCodec", httpServerCodec)
            .replace(this, "HttpServerUpgradeHandler", httpServerUpgradeHandler);
    }
Creates the channel handler provide cleartext HTTP/2 upgrade from HTTP
upgrade or prior knowledge

@param bizGroup                 the EventLoopGroup
@param httpServerCodec          the http server codec
@param httpServerUpgradeHandler the http server upgrade handler for HTTP/2
@param http2ServerHandler       the http2 server handler, will be added into pipeline
                                when starting HTTP/2 by prior knowledge
remoting/remoting-http/src/main/java/com/alipay/sofa/rpc/transport/http/Http2ServerUpgradeHandler.java