Portlets and portlet container

Portals are implemented in various technologies. In this book, we will focus on J2EE technology and portal implementation on that platform.

As with any other API or feature in J2EE, portal and portal server implementations are governed by commonly-agreed industry standards and specifications. JSR-168 and JSR-286, also called the Portlet Specifications, govern the standards for portal technology on the J2EE platform. Before we go further into the portal server architecture, let us review some terminology.

The components of this figure are described here:

Constructing a view

Let us look at an example of how these components are used. The following figure shows a high-level view of how a portal processes a request, and the specific role of the components of the portal:

As we can see, the browser makes the request for a portal page, which is then passed to the portal container by the server that had originally received the request. The container determines the appropriate page and passes the request to it. The portal page identifies all the portlets contributing to it, and aggregates all the page fragments generated by each portlet. Each portlet independently follows its own life cycle and generates the final fragment. The combined page is then passed back to the container, which then passes the response back to the server. The server aggregates the information along with its own features, and returns the response to the browser, which formats the HTML for the user.

Portal specification and WSRP

JSR-168 and JSR-286 are Java Portlet Specifications that define the standard for the Java Portlet API. Like other specifications, the portlet API specification is intended for both portlet developers and portal server creators. Standardizing on a portlet API allows the creation of pluggable portlets that are independent of the portal server. Hence, the portlets created on one platform can be easily migrated to another.

The Web Services for Remote Portlets(WSRP) specification defines a protocol for creating and communicating with remote portlets. It is not intended to compete with the portlet specifications; instead, it facilitates web services based communication between portlets created using the specification. Because application integration is the primary function of portals, utilizing web services for integration can be an efficient mechanism.

Servlets and portlets

J2EE Servlets and Portlets share a lot of features. Both are Java-based web components, whose life cycles are managed by the container, interacting with browser clients, servicing requests, and responding to them. Both are also responsible for generating dynamic content to create the user interface of the web application. However, portlets differ from servlets in terms of scope and functionality in the following ways:

The expectations from portals are different from traditional web sites. Hence, the portlet specifications have to be created independently of servlets.

However, this doesn't preclude portals from interacting with servlets. A portlet can effectively invoke any servlet, JSP, or a JSP tag, and leverage their functionality to fulfill its function.