How Portlets are different from traditional Servlets?


If we talk about a web application, Servlets provide content that normally takes up the whole web page in a browser (unless you're using frames), and we talk about portlet application, portlets provide content that is wrapped by a window. With portlets, you can have multiple portlets side by side with one another and each one can provide content and functionality that is different from the other. A portlet can provide the complete interaction for one type of application, while another portlet can provide content for another type of application. The portal can provide some house keeping functionality and secured single point of entries to all of the portlets on a page.

Here are some similarities:
  • Servlets and portlets are web based components that utilize Java for their implementation.
  • Portlets are managed by a portlet container similar to a servlet container.
  • Both of these components generate content, which can be static or dynamic.
  • Both portlets and servlets have a life cycle that is controlled by the container.
  • The client/server model is used for both servlets and portlets.
  • The packaging and deployment are essentially the same.
  • The manner in which the classes are loaded and the class loaders that perform the work are also the same.
  • Lifecycle management is similar.
  • The Request and Response semantics are also similar.
Here are some differences:
  • Servlets can provide complete web pages, whereas portlets only provide fragments. These fragments are then aggregated to form a complete web page by the portal.
  • Portlets aren’t allowed to generated HTML code that contains tags such as base, body, frame, frame set, head, HTML, or title. The iframe tag can be used with caution.
  • The user cannot access a portlet directly using a URL in the way that a servlet is accessed. Instead, the URL points to the page containing all of the portlets on one page.
  • Communication between the web client and the portlets is performed through the portal.
  • Portlets can be provided with buttons or controls to manipulate the portlets’ window states or portlet modes.
  • Multiple instances of a single portlet can be placed onto the same page
  • Portlets support persistent configuration and customization.
  • Portlets also support user profile information.
  • Portlets support two scopes within the session; application scope and portlet scope.
There are several things that servlets are allowed to do, but portlets aren’t.
  • Portlet aren’t allowed to set the character set encoding of the response.
  • Portlet also aren’t allowed to set the HTTP headers on the response. Portlet cannot manipulate the URL of the client request to the portal.

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