使用PrintWriter对象将List对象从Java Servlet发送到JSP？

Question

Before proceeding I realise that there's a similar question ( Passing a List from Servlet to JSP ) from a couple of years ago. I realise that it is possible to set the list I'm trying to pass as a session attribute but out of curiosity I wondered if it's possible to use the PrintWriter object to send the data back to the JSP page.

<script type="text/javascript">
        function getEngineSchemes(engineID) {
            $.get('SchemeTypeServlet', {
                action: "getSchemes",
                engineID: engineID
            },
            function(data, status){

            }).fail(function() {
                alert("Error obtaining schemes for engine with engine id: " + engineID);
            });
        }
    </script>
</body> 

@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    //Set type of response
    response.setContentType("text/html");
    response.setCharacterEncoding("UTF-8");
    //get parameters that may be passed from client to determine which methods should be called
    String action = request.getParameter("action");

    if(action.equalsIgnoreCase("getSchemesForEngine")) { 
        Integer engineID = Integer.parseInt(request.getParameter("engineID"));
        List<String> schemeNames = getSchemeNamesForEngine(engineID);

        response.getWriter(). //insert code to send object back to JSP
        response.getWriter().flush();
    }       

One solution I think may be reasonable would be to create a JSONObject and have something along the lines of

response.setContentType("application/json");
JSONObject json = new JSONObject();
     for(String name : schemeNames) {
            json.put(engineID, name);
         }
    response.getWriter().write(json.toJSONString());
    response.getWriter().flush();

I haven't tested the above code but I just want to know if that seems like the best solution to my problem or if I'm making it overly complicated? Maybe there's a far simpler solution to my question.

Answer 1

I think you are having things messed up in your head. First of all, you cannot sent text or any kind of data from a servlet to a jsp. The proper way to do this is to use the session and use response.sendRedirect or RequestDispatcher.forward methods. But this will ignore any calls made before to the servlet's Writer Object.