When an edge proxy is implemented using SIP Servlets, the application inserts the flow token into the request as explained in RFC 5626. The application can retrieve flow tokens from the Flow object for that purpose.

Example 8-4 illustrates how an application might implement this logic.

@Register
public void handleRegister(SipServletRequest request){
  Proxy proxy = request.getProxy();
  Flow flow = proxy.getFlow();
  proxy.setAddToPath(true);
  SipURI pathURI = proxy.getPathURI();
  pathURI.setUser("edge");
  pathURI.setParameter("flow", flow.getToken());
  pathURI.setParameter("ob", "true");
  proxy.proxyTo(request.getRequestURI());
}

Similarly, when a different request that needs to be forwarded to a UA arrives at the edge proxy, it can look up the Flow object using the flow token present in the request. After the retrieved flow object is set on the Proxy (or ProxyBranch) by using the Proxy.setFlow(Flow flow) or ProxyBranch.setFlow(Flow flow) methods, the SIP Servlet container uses the corresponding transport association to send the message.

Example 8-5 illustrates one such implementation.

@Invite
public void handleInvite(SipServletRequest request) {
  Address route = request.getPoppedRoute();
  String flowToken = route.getURI().getParameter("flow");
  Proxy proxy = request.getProxy();
  Flow flow = sipServletContext.getFlow(flowToken);
  proxy.setFlow(flow);
  proxy.proxyTo(request.getRequestURI());
}