You need to use what is called a "plug-in". A plug-in is a weblogic-made component which can be hooked into your web server. There are specific plug-ins available for popular web servers such as Apache or Microsoft IIS.

In a cluster of weblogic servers, the plug-in is able to read weblogic-specific cookies and route the request to the weblogic server containing the user's state. Click here for more details.