CODEWITHSUNDEEP
javaservlets
SK176H
SK176H

Reputation: 1319

HttpSessionBindingListner methods not being called

I am trying a HttpSessionBindingListener example and the events are not firing. What am i doing wrong here.

Here is the code for the Attribute class that i am trying to set and the code for the servlet class.

The servlet is working but is not displaying the output that i am expecting.

    public class SimpleAttribute implements HttpSessionBindingListener {

        PrintWriter writer;

        public  SimpleAttribute(PrintWriter writer) {
            this.writer = writer;
        }

        public void valueBound(HttpSessionBindingEvent event) {
            writer.write("Value bound called");
            writer.write("<br/>");
        }

        public void valueUnbound(HttpSessionBindingEvent event) {
            writer.write("value Unbound called");
            writer.write("<br/>");


}
}




public class SessionBindingServlet extends HttpServlet {

    private static final String SIMPLEATTR = "simpleattribute";

    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws IOException {

        ServletContext servletContext = getServletContext();            
        PrintWriter out = response.getWriter();
        response.setContentType("text/html");
        try {
            servletContext.removeAttribute(SIMPLEATTR);
            out.write("removed previous attribute successfully");
            out.write("<br/>");
        } catch (Exception e) {

        }

        servletContext.setAttribute(SIMPLEATTR, new SimpleAttribute(out));
        out.write("Added simple attribute successfully");
        out.write("<br/>");
    }
}

Upvotes: 0

Views: 711

Answers (2)

Amir Pashazadeh
Amir Pashazadeh

Reputation: 7302

There are many issues in your code:

  • A HttpSessionBindingListener is notified if the object which implements the interface is bound/unbound to session, not other objects. If you need to be informed by attributes set/get on session, you shall implement HttpSessionAttributeListener.
  • Have you registered your listener in web.xml?
  • And finally HttpSessionAttributeListener is get notified on session attribute changes not servlet-context attribute changes, if you want that you shall implement ServletContextAttributeListener.

Upvotes: 0

Sotirios Delimanolis
Sotirios Delimanolis

Reputation: 279890

You haven't actually bound the object to an HttpSession, you've bound it to the ServletContext.

You should be retrieving the HttpSession with

HttpSession session = request.getSession(true);

and adding the attribute

session.setAttribute(SIMPLEATTR, new SimpleAttribute(out));

That will fire an HttpSessionBindingEvent which will notify your HttpSessionBindingListener implementing class object.

Upvotes: 2

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