I am trying to build a response for a request that is saved in hashmap. But I am not sure how can I solve this problem - should I use async mechanism or multithreading and how? 
Can I use some kind of asynchronous mechanism or multithreading use? But I am super struggling with this? Even simplifying this approach would be great. But I must send the data received in the POST request back to request A. Please advise on how to progress on this.
    Map<String, HttpServletRequest> requestLookup = new HashMap<>();
    public void handle(String target, Request jettyReq, HttpServletRequest request, HttpServletResponse response) {        // Redirect API control based on HTTP method type
        if (request.getMethod().equals(constGetRequest)) {
            getObject(jettyReq, request, response);
        }
        if (request.getMethod().equals(constPostRequest)) {
            writeGetObjectResponse(jettyReq, request, response);
        }
        jettyReq.setHandled(true);
    }
    public void doGET(Request jettyReq, HttpServletRequest request, HttpServletResponse response) {
        requestLookup.put(xRequestId, request);
        String requestURI = request.getRequestURI();
        String[] strs = requestURI.split("/");
        for (String str : strs) {
            System.out.println("item:" + str);
        }
        String object_key;
        String bucket_name;
        String lambdaFunc;
        if (strs.length <= 2) {
            try {
                throw new Exception("Can not get bucket and object key info");
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
        bucket_name = strs[1];
        System.out.println("Handler -- bucketName received = " + bucket_name);
        // Redis class contains the mapping of bucket_name and function name to be executed in the Python server
        lambdaFunc = redis.getFuncFromRedis(bucket_name); // example function - "".upper()
        object_key = requestURI.substring(requestURI.indexOf(bucket_name) + bucket_name.length() + 1);
        System.out.println("objectKey = " + object_key);
        S3ObjectReader getObject = new S3ObjectReader(); 
        response.setContentType("text/html;charset=utf-8");
        response.setStatus(HttpServletResponse.SC_OK);
        List<String> result = getObject.printOriginalObjectContent(bucket_name,object_key);
        System.out.println("Print original object content:");
        for (String s : result) {
            System.out.println(s);
        }
        System.out.println("Print transformed object content:");
        LambdaFunctionConnector connectLambdaFunc = new LambdaFunctionConnector();
        connectLambdaFunc.sendRequest(lambdaFunc,result);
    }
    public void  doPOST(Request jettyReq, HttpServletRequest req, HttpServletResponse res) {
        // retrieve request from the lookup table       String requestID = request.getHeader("X-Request-ID");
       HttpServletRequest originalRequest = requestLookup.get(requestID);    }