Portlet Vs. Servlet

•  With servlets, the service() method processes all requests.
•  With portlets, the processAction() method processes the requests and the render() method draws the    contents of the portlet on the page.

Portlets have additional characteristics that make them different
from Servlets

•  Portlet Modes
•  Window States
•  Portlet Preferences 

Portlet Modes :  Each portlet has a current mode, which indicates the function the portlet is performing.
All JSR 168 compliant portals should support the View, Edit and Help modes.

Window States :Window states indicate the amount of portal page space that will be assigned to a portlet.
 All spec compliant portals should support the minimized, maximized and normal window states.

Portlet Preferences :Portlets can be configured to provide a custom view or behavior for different users.
 For example, a any portlet can show the other view in Ahmedabad for one user and the different view in Banglore for anotheruser. These configurations are represented as a persistent set of name-value pairs and are referred to as portlet preferences.