Enabling HttpSession Support - Atmosphere/atmosphere Wiki

By default, the Atmosphere Framework doesn't create sessions and isn't using them. If your application uses HttpSession, you need to tell Atmosphere to track the session as well by enabling it, in web.xml / application.xml:

<listener>
    <listener-class>org.atmosphere.cpr.SessionSupport</listener-class>
</listener>
...
<context-param>
    <param-name>org.atmosphere.cpr.sessionSupport</param-name>
    <param-value>true</param-value>
</context-param>

This is specially important if you are using WebSocket because of the difference of WebServer implementation, the framework will makes sure it works uniformly with all of them.