How to reuse Request in DispatchInterceptor?

ENV
ICE: 3.7.1
JDK: 10.0
WINDOWS 10

My case:
Node_A will send a request to Node_B，then the Node_B will handle the request locally, and it will forward the request to Node_C.
Here is my code sample:

public class ForwardInterceptor extends DispatchInterceptor {
    @Override
    public CompletionStage<OutputStream> dispatch(Request request) throws UserException{


        Identity identity = request.getCurrent().id;
        String serviceName = request.getCurrent().id.name;
        String operation = request.getCurrent().operation;
        Map<String, String> context = request.getCurrent().ctx;

        //get all dest node ids
        List<String> destNodeIdList = JSON.parseArray(context.get("DestNodeId"));



        Object servant = NodeContext.findServant(identity);
        if (servant != null) {
            if(destNodeList.size()<=1){
                //just only dispatch the request to local servant
                return servant.ice_dispatch(request);

            }else{

                //step 1: dispatch the request to local servant
                servant.ice_dispatch(request);              

                //step 2:remove current node Id from destNodeIdList

                //step 3: forward the request to other-nodes
                for(String destNodeId : destNodeIdList){
                    Session destSession = SessionManager.getSession(destNodeId);
                    ObjectPrx base = destSession.getProxy(serviceName);

                    //Error, How to retrieve byte[] inParams from request object?
                    byte[] inParams = getInParams(request); 
                    base.ice_invoke(operation, com.zeroc.Ice.OperationMode.Normal, inParams, context);  

              }
            }
        }
    }


    private byte[] getInParams(Request request){
      Incoming in = (Incoming)request;
      byte[] inParams = in.readParamEncaps();
      in.startOver();
      return inParams;
    }
}