Building Portlets with JavaBeans Developer's Overview August 2001

Portals and Portlets

A portal is a Web page that displays data from other sources. Increasingly, developers are using portal software to offer employees, customers, and partners personalized views of applications and information.

Oracle9iAS Portal provides a common, integrated starting point for accessing data from a variety of sources:

• Web Sites: Content from any internal or external Web page, such as stock quotes, news headlines, or travel services.
• Content Areas: Portal entities that hold self-published information (such as documents, spreadsheets, and presentations) in the form of folders and items. Portal pages can link one or more content areas together for better organization and controlled access.
• Applications: Web-enabled applications.
• Custom Sources: Content and application pieces built using the PDK.

Oracle9iAS Portal pages display content in regions called portlets. You can think of portlets as "Web components" that display data from other Web sites and applications and generate summaries of key information. Portlets provide a standardized, reliable, secure way to represent and package enterprise information; they provide at-a-glance views of data from various sources both inside and outside of a corporate network. By assembling many portlets onto one page, you can give end-users a centralized place to perform their daily business tasks.

From a developer's perspective, portlets are PL/SQL procedures or Java servlets that execute on the server. Oracle9iAS Portal renders portlets dynamically in nested HTML tables, with the output of each portlet displayed in a cell. Typically, portlets use standard HTML to display information to users, but their interfaces can be extended using other browser-capable technologies such as Cascading Style Sheets (CSS), eXtensible Markup Language (XML), eXtensible Style Language (XSL), JavaScript, and Java applets.

Oracle9iAS Portal provides simple self-service tools for building portlets, and you can use other tools, including Oracle JDeveloper and the PDK. The PDK-Java provides services you can use to create portlets from existing Java applications, servlets, and JSPs. It provides an abstraction to handle communication with Oracle9iAS Portal, default classes to simplify portlet creation, and exposes methods for end-user customization, session storage, security, and logging.

Providers

In the Oracle9iAS Portal architecture, the portal never talks to a portlet directly. Instead, it communicates via an entity called a provider that represents and manages one or more portlets. A portlet provider is a Java class or PL/SQL package that exposes a data source or application to Oracle9iAS Portal. The best example of a portlet provider is Oracle9iAS Portal itself: features including security, administration, application building, and self-service publishing are exposed as portlets.

By implementing functions that interact with Oracle9iAS Portal, providers give a framework for portlets to work within. A portlet provider has the following characteristics:

• Provides a communication link between the portal services and portlets.
• Implements session startup and provider login.
• Acts as a proxy to all portlet calls.
• Manages the portlet repository list.

You can expose portlets through two kinds of providers:

• Database providers are best for portlets that are executed within the database or require significant interaction with the database, and in situations where the development team has extensive Oracle experience.
• Web providers are best for leveraging existing code or external information sources, when the portlets reside on machines other than Oracle9iAS Portal nodes, and in development groups that have extensive Web development background.

This article and the accompanying case study focus on Web providers. For more information about Database providers, see Understanding Database Providers.

The main purpose of the PDK-Java is to simplify portlet implementation while representing the provider architecture in a natural way to Java developers. There are four functional areas:

• The Provider Adapter (oracle.portal.provider.v1.http.HttpProvider) handles HTTP communication.
• The Provider Interfaces specify the functions a provider and its portlets require to operate as part of the portal page.
• The Provider Runtime provides a base implementation of the Provider interfaces in the class oracle.portal.provider.v1.http.DefaultProvider.
• The Provider Utilities provide methods for rendering portlets.

The DefaultProvider (which implements the Provider Runtime) is the first line of communication from the portal (through the Provider Adapter) when retrieving portlet information and rendering a portlet. Once intialized by Oracle9iAS Portal, the DefaultProvider uses its methods to answer all of the requests from Oracle9iAS Portal.

The DefaultProvider gets information about a portlet by parsing a static XML file named provider.xml. Click here to display the provider.xml file used in the case study that accompanies this article.

Created by the portlet developer, a provider.xml file has the following characteristics:

• It describes the provider, including the name of the class that implements the provider.
• It describes the portlet(s) the provider manages. Each portlet description includes:
  • Portlet ID, portlet name, portlet title, and portlet description.
  • Implementation modes of the portlet such as renderer, security manager, and personalization manager.

At runtime, the DefaultProvider locates provider.xml by using the "provider_root" argument from the Oracle HTTP Server (Oracle9i Application Server). Once located, the DefaultProvider parses this file and creates an instance (Java object) for each portlet specified in the file. It associates each of the portlet tags with each newly-created portlet instance. The DefaultProvider then creates an instance for each render mode specified in provider.xml and associates it with the value of its portlet tag. Finally, the DefaultProvider creates a list of portlets and adds each newly-instantiated portlet to the list. At this point, Oracle9iAS Portal can render the portlet.

Rendering

Portlets generate text, such as HTML or XML, that browsers use to draw what the portlet looks like. The act of generating this text for display is called portlet rendering.

Because portlets are displayed in browsers, they can use most techniques that browsers support, including JavaScript, Java applets, and plug-ins. Plain HTML is the most basic way to render portlets and provides a great deal of flexibility. You can use standard HTML paradigms such as links, forms, images, tables, and any construct that can be displayed within an HTML table cell. A few constructs (such as frames) cannot be used simply because they cannot be displayed in a table cell.

When the user views a page containing a Web provider portlet, Oracle9iAS Portal calls the portlet’s render manager to render the portlet’s content. The portlet content can be rendered in several modes that can be made available to end-users and administrators, as appropriate.

Conclusion

Oracle9iAS Portal provides a starting point for accessing data from diverse sources. Oracle9iAS Portal pages render content in portlets that display data from other Web sites and applications and generate summaries of key information. Oracle9iAS Portal provides simple self-service tools for creating portlets, and you can build portlets with a variety of tools, including Oracle JDeveloper and Oracle9iAS Portal Developer Kit. In addition to providing abstractions for the underlying communications mechanisms, the PDK services include methods for end-user customization, session storage, security, and logging.

OTN's Oracle9iAS Portal Community page provides resources for learning about and using Oracle9iAS Portal and the PDK. It also provides Portal Studio, a hosted developer service that you can use to build and deploy Web portlets without having to install Oracle9iAS Portal yourself.

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