If you have already developed servlets/JSPs, your first question will be: how do Application Designer sessions relate to HTTP sessions?
Application Designer adapters are living in sessions which are administered inside the Application Designer runtime environment. The sessions are kept in parallel to HTTP sessions, i.e. HTTP sessions may be used by other servlets/JSPs that may be part of your web application - but Application Designer itself does not require them. It is no problem to reach HTTP sessions from an adapter object via an API.
Why is Application Designer not using straight HTTP sessions? The problem is that HTTP sessions are sometimes the same for multiple browser instances. If you open a new browser instance from an existing browser instance (for example, with the Internet Explorer), then the corresponding session object on the server is shared between the browser instances. In the Application Designer session management, each instance of a browser (and if you want: each frame inside one browser) has its own clearly assigned session.
The above diagram shows the following:
There are three browser instances sharing one HTTP session.
Each browser instance has one related Application Designer session.
There is an API from the Application Designer runtime to access the HTTP session.
