Developing a Java Portlet is
similar to the process of developing a Servlet based web applications. The
main differences are:
• The portlet only produces a
fragment of the final HTML and not the full markup. The portal will join
the fragments of several portlets
and will create the full page returned to the user.
• The class receiving the
requests has to inherit from javax.portlet.Portlet instead of
javax.servlet.http.HttpServlet.
• A portlet request may involve a
two phase process:
1. On each request at most one
portlet will be able to perform an state-changing operation. This is
referred to as the Action phase
and is implemented through a method called processAction.
Not always an action phase is
needed. Requests that involved an action phase are invoked to an
URL known as an ActionURL, while
those that only have a render phase are invoked through a
RenderURL.
2. Next is the render phase where
all other portlets related to the page that is going to be returned may
be called in any order to produce
the HTML fragment to draw themselves. Portlet implement this
functionality through a method
called render.
• Existing web application
development frameworks such as Struts, JSF, Webworks, etc can be used
through the use of Bridges. Other
existing frameworks have been adapted to be usable directly
without the need of a bridge. An
example is the Spring Portlet MVC framework.
A portlet container is a server
side software component that is capable of running portlets. A portal is a
web application that includes a
portlet container and may offer additional services to the user. Liferay
Portal includes its own portlet
container and offers lots of functionalities such as user and organization
administration, creation of
virtual communities, having pages based on portlet layouts, graphical
selection of portlets and
drag&drop to place them, grouping pages into websites, several bundled
ready-to-use portlets, and much more.
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