How can I manually load a Java session using a JSESSIONID?

Question

I have a servlet which handles a multipart form post. The post is actually being made by a Flash file upload component embedded in the page. In some browsers, the Flash-generated POST doesn't include the JSESSIONID which is making it impossible for me to load certain information from the session during the post.

The flash upload component does include cookie and session information within a special form field. Using this form field, I can actually retrieve the JSESSIONID value. The problem is, I don't know how to use this JSESSIONID value to manually load that specific session.

Edit - Based on ChssPly76's solution, I created the following HttpSessionListener implementation:

    @Override
    public void sessionCreated(final HttpSessionEvent se) {
        final HttpSession session = se.getSession();
        final ServletContext context = session.getServletContext();
        context.setAttribute(session.getId(), session);
    }

    @Override
    public void sessionDestroyed(final HttpSessionEvent se) {
        final HttpSession session = se.getSession();
        final ServletContext context = session.getServletContext();
        context.removeAttribute(session.getId());
    }

Which adds all sessions to the ServletContext as attributes mapped by their unique ids. I could put a Map of sessions in the context instead, but it seems redundant. Please post any thoughts on this decision. Next, I add the following method to my servlet to resolve the session by id:

    private HttpSession getSession(final String sessionId) {
        final ServletContext context = getServletContext();
        final HttpSession session = (HttpSession) context.getAttribute(sessionId);
        return session;
    }

Answer 1

There is no API to retrieve session by id.

What you can do, however, is implement a session listener in your web application and manually maintain a map of sessions keyed by id (session id is retrievable via session.getId()). You will then be able to retrieve any session you want (as opposed to tricking container into replacing your current session with it as others suggested)