[FIXED] Attributes not being saved in an HTTP session on multiple requests

Issue

I want to create a session in a servlet that I can add data to as multiple requests are coming in. I first check if the session is null, if it is, I get the session and store initial attributes in it. This is what I am hoping for on the first request to the servlet. For further requests, the session should exist and I modify data to the attributes in my session. But in my else condition, my attributes do not exist. How can I get the session to persist through multiple request? thank you

protected void processRequest(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    response.setContentType("text/html;charset=UTF-8");
    try (PrintWriter out = response.getWriter()) {
        int quantity = 0;
        Item[] item = new Item[9];
        int currRow = Integer.parseInt(request.getParameter("rowNum"));

        HttpSession session = request.getSession(false);
        if (session == null) {
            session = request.getSession();
            for (int i = 0; i < 9; i++) {
                item[i] = new Item();
                item[i].setID(request.getParameter("ID" + (i + 1)));
                item[i].setPrice(Double.parseDouble(request.getParameter("p" + (i + 1))));
                session.setAttribute(Integer.toString((i + 1)), item[i]);

            }
            quantity = Integer.parseInt(request.getParameter("q" + currRow));
            Item currItem = (Item) session.getAttribute(Integer.toString(currRow));
            currItem.setQuantity(currItem.getQuantity() + quantity);
            session.setAttribute(Integer.toString(currRow), currItem);
        } else {

            if (null == session.getAttribute("2")) {
                out.println("not exist");
            } else {
                out.println("exist");
            }
        }

    }
}

FIX:

protected void processRequest(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    response.setContentType("text/html;charset=UTF-8");
    try (PrintWriter out = response.getWriter()) {
        int quantity = 0;
        Item[] item = new Item[9];
        int currRow = Integer.parseInt(request.getParameter("rowNum"));

        HttpSession session = request.getSession();
        Item currItem;

        if (session.getAttribute("1") == null) {
            for (int i = 0; i < 9; i++) {
                item[i] = new Item();
                item[i].setID(request.getParameter("ID" + (i + 1)));
                item[i].setPrice(Double.parseDouble(request.getParameter("p" + (i + 1))));
                session.setAttribute(Integer.toString((i + 1)), item[i]);
            }
            quantity = Integer.parseInt(request.getParameter("q" + currRow));
            currItem = (Item) session.getAttribute(Integer.toString(currRow));
            currItem.setQuantity(currItem.getQuantity() + quantity);
        } else {
            quantity = Integer.parseInt(request.getParameter("q" + currRow));
            currItem = (Item) session.getAttribute(Integer.toString(currRow));
            currItem.setQuantity(currItem.getQuantity() + quantity);
        }
}

Solution

You can just use request.getSession() instead of request.getSession(false); and the subsequent null check.

It will create a new one if none exists or use the existing one when it is found. The java docs for HtpServletRequest

Answered By - superbAfterSemperPhi