code: private void configureClearTextWithHttpUpgrade(SocketChannel ch) {
          HttpClientCodec sourceCodec = new HttpClientCodec();
          Http2ClientUpgradeCodec upgradeCodec = new Http2ClientUpgradeCodec(connectionHandler);
          HttpClientUpgradeHandler upgradeHandler = new HttpClientUpgradeHandler(sourceCodec, upgradeCodec, 65536);
  
          ch.pipeline().addLast(sourceCodec,
              upgradeHandler,
              new UpgradeRequestHandler(),
              new UserEventLogger());
      }
docs: Configure the pipeline for a cleartext upgrade from HTTP to HTTP/2.