Servlets vs Portlets

• Portlets are not accessible by a URL. Portlets are intended to be part of a page, as opposed to being independent pages.

• Browsers and web clients interact with portlets through the portal server. Portlets can neither set HTTP headers, nor be aware of the client URL.

• The portal server provides a customized subset of the request object to a portlet.

• Portlets only contribute a fragment of the HTML page that is eventually presented to the browser, and not the whole page. A portal server aggregates these fragments from various portlets to create a final page.
  

• Portlets come with certain modes and window states that make them function independently of the whole page behavior.
  

• Portlets have access to some specialized functionality that allows storage of states and preferences across requests and sessions.