Session Tracking: Behind the Scenes

If cookies fail, url rewriting is handled by

//return the new url
public String HttpServletResponse.encodeURL(String url);

If you feel nosy, you can get the actual is string with
```
public String HttpSession.getId();
```
You can build an object that gets a callback whenever it is bound or unbound by having it implementing the javax.servlet.http.HttpSessionBindingListener interface. The callbacks you need to implement are
```
public void HttpSessionBindingListener.valueBound(HttpSessionBindingEvent event);
public void HttpSessionBindingListener.valueUnbound(HttpSessionBindingEvent event);
```