JSP / Servlets会话+ PHP：跟踪会话 - JSON /数据库或HttpSessionListener？

I have implemented a Servlet, and a PHP site is accessing that Servlet to retrieve data. I'm wondering what is the best method to store a session variable, or whether I should store it at all.

Variables which need to be stored include an ArrayList, and other objects.

I've thought through about 3 possibilities:

(1) Implement the HttpSessionListener, and store each session (when it's created) into a static SessionMap. Then delete the session once it is destroyed.

(2) Store everything in JSON. So I'll have to serialize/deserialize each Object and pass it back and forth. (I have a list of items in each ArrayList/Object I want to keep track of between user clicks.)

(3) Store the information in MongoDB (just to pick one), using the SessionID as the primary key.

What do you guys think?

I rather like a combination of all three.

  1. Has the advantage of simplicity - no need to go to a database if there's a session available.
  2. JSON is lightweight, and it's the language of the browser.
  3. Storing items in a database and retrieving them using session ID allows the possibility of users starting a session, leaving it in an incomplete state, and coming back later to pick up where they left off. The database might be a nice way to store information if the memory requirements become large and cumbersome.

I don't believe it has to be an exclusive choice.

The HttpSessionListener is unnecessary here. All you basically need to do in the servlet is:

List<String> links = (List<String>) request.getSession().getAttribute("links");
if (links == null) {
    links = new ArrayList<String>();
    request.getSession().setAttribute("links", links);
}
links.add(request.getParameter("link"));

The attributes will be garbaged anyway when the session get destroyed.

JSON only adds unnecessary overhead and a database is only beneficial when there's not much memory space in webserver (however, DB's in turn also eats memory to a certain degree).

I only wonder how you think to maintain the same servlet session from PHP on. This would involve invoking the servlet using JSESSIONID attribute in URL (bad idea) or a PHP script with curl acting as a proxy (why not just doing it all in PHP?). Or is it running on the same domain? Or are you using Quercus to run PHP on a Java servletcontainer?