RequestDispatcher.include is working only once

Question

I am trying to output the rendering of a JSP page using RequestDispatcher.include() in the following method:

public static String readTemplate(HttpServletRequest request, HttpServletResponse response, String template) {
    HttpServletResponseWrapper responseWrapper = new HttpServletResponseWrapper(response) {
        private final StringWriter sw = new StringWriter();

        @Override
        public PrintWriter getWriter() throws IOException {
            return new PrintWriter(sw);
        }

        @Override
        public String toString() {
            return sw.toString();
        }
    };

    String templateFile = "/templates/" + template + ".jsp";
    logger.log(Level.INFO, "Reading template {0} ...", templateFile);

    try {
        request.getRequestDispatcher(templateFile).include(request, responseWrapper);

    } catch (ServletException | IOException | IllegalStateException e) {
        logger.log(Level.SEVERE, e.getMessage());
    }

    logger.log(Level.INFO, "Completed reading template {0}", templateFile);

    // retrieve HTML from response
    return responseWrapper.toString();
}

The method is part of a servlet I am running with Tomcat8. This works perfectly the first time, but hangs at the include call the second run (i.e. if I click refresh on the browser).

I have already verified the dispatcher is not null.

This is what I can see from the catalina.log (cleaned for your review)

First run:

26-Feb-2015 17:41:17.921 INFO [http-nio-8081-exec-2] ism.Reports.readTemplate Reading template /templates/INCIDENT_REPORT.jsp ...
26-Feb-2015 17:41:18.046 INFO [http-nio-8081-exec-2] ism.Reports.readTemplate Completed reading template /templates/INCIDENT_REPORT.jsp

Second run (response never returns, i.e. browser always loading page):

26-Feb-2015 17:41:26.327 INFO [http-nio-8081-exec-8] ism.Reports.readTemplate Reading template /templates/INCIDENT_REPORT.jsp ...

This does not change until I reboot Tomcat.

Can someone explain what am I doing wrong or at least how to debug this? Thanks!

EDIT 1: Forgot to say the method is static, but I also tried making it not static didn't make any difference

I don't see why it would cause the problem you're seeing, but returning a new PrintWriter every time the method is called is a bad idea. You should always return the same PrintWriter. — JB Nizet, Feb 26 '15 at 17:12
Thanks @JBNizet will do that, but still I need to figure out what is happening there.... — Fabrizio Prosperi, Feb 27 '15 at 07:55

score 0 · Accepted Answer · answered Feb 27 '15 at 13:44

The code above is working, I realized where the issue was. The included JSP page was opening many MySQL connections but only one was closed. Hence the second request was waiting for the MYSQL resources to be freed before performing the task. I am very sorry I didn't notice this until now, and I didn't even mention MySQL connections in the first place. I guess not receiving replies here lead me to find the solution on the JSP file itself.

RequestDispatcher.include is working only once

1 Answers1