protected void doRegister(SipServletRequest req) throws ServletException, IOException {
    logger.info("Received register request: " + req.getTo());
    int response = SipServletResponse.SC_OK;
    SipServletResponse resp = req.createResponse(response);
    HashMap<String, String> users =
        (HashMap<String, String>) getServletContext().getAttribute("registeredUsersMap");
    if (users == null) users = new HashMap<String, String>();
    getServletContext().setAttribute("registeredUsersMap", users);

    Address address = req.getAddressHeader(CONTACT_HEADER);
    String fromURI = req.getFrom().getURI().toString();

    int expires = address.getExpires();
    if (expires < 0) {
      expires = req.getExpires();
    }
    if (expires == 0) {
      users.remove(fromURI);
      logger.info("User " + fromURI + " unregistered");
    } else {
      resp.setAddressHeader(CONTACT_HEADER, address);
      users.put(fromURI, address.getURI().toString());
      logger.info("User " + fromURI + " registered with an Expire time of " + expires);
    }

    resp.send();
  }
    public void handleResponse(SipResponse response) {
      _response = response;

      int status = response.getStatus();

      if (status == 100) return;

      if (_tx.isCompleted() && !response.is2xx()) {
        if (LOG.isDebugEnabled())
          LOG.debug("Dropping response " + response.getStatus() + " since proxy is completed");
        return;
      }

      if (LOG.isDebugEnabled()) LOG.debug("Got response {}", response, null);

      SipRequest request = _tx.getRequest();

      Session session = request.session();

      if (request.isInitial() && status < 300) {
        if (!session.isSameDialog(response)) {
          AppSession appSession = session.appSession();
          Session derived = appSession.getSession(response);
          if (derived == null) derived = appSession.createDerivedSession(session);
          session = derived;
        }
      }

      response.setSession(session);
      if (status < 300) session.updateState(response, false);

      response.removeTopVia();
      response.setProxyBranch(this);

      if (status < 200) {
        if (response.isInvite()) updateTimerC();

        invokeServlet(response);
        forward(response);
      } else {
        _actives--;

        stopTimerC();

        if ((300 <= status && status < 400) && _branchRecurse) {
          try {
            Iterator<Address> it = response.getAddressHeaders(SipHeaders.CONTACT);
            while (it.hasNext()) {
              Address contact = (Address) it.next();
              if (contact.getURI().isSipURI()) {
                Branch branch = addTarget(contact.getURI());
                if (branch != null) {
                  _recursedBranches = LazyList.add(_recursedBranches, branch);
                  branch.setRecurse(_branchRecurse);
                }
              }
            }
          } catch (ServletParseException e) {
            LOG.ignore(e);
          }
        }

        if (_best == null
            || (_best.getStatus() < 600 && (status < _best.getStatus() || status >= 600))) {
          _best = response;
        }

        if (status >= 600) {
          SipProxy.this.doCancel(null, null, null);
        }

        if (status < 300) {
          invokeServlet(response);
          forward(response);

          SipProxy.this.doCancel(null, null, null);
        } else {
          if (LazyList.size(_targets) > 0) startProxy();

          if (_actives > 0) {
            response.setBranchResponse(true);
            invokeServlet(response);
          } else {
            tryFinal();
          }
        }
      }
    }