Portlets

Portlets are pluggable user interface components that run inside a portal container and produce content to be displayed on a portal page. They are designed to be aggregated with other portlets and pages, enabling a single web portal to present multiple, independently developed applications within a unified user interface. Portlets differ from traditional servlets in that they are intended for inclusion in a portal page and interact with the surrounding portal framework and other portlets rather than standing alone.

Architecture and lifecycle: Portlets execute within a portal server or container that manages their execution and state. Each portlet instance goes through a lifecycle that includes action, render, event, and resource phases. The action phase handles user input and may update internal state; the render phase produces the markup fragment for display; the event phase supports communication between portlets; the resource phase serves non-HTML resources such as JSON or binary data. Portlets support window states (such as normal, minimized, and maximized) and render modes (such as view, edit, and help), along with preferences that store configuration data for individual users or portlets.

Standards and interoperability: The Java Portlet API defines the interfaces and lifecycles used by portlets. The original standard, JSR 168, established portlets and their basic lifecycle; subsequent editions, such as JSR 286, added features for resource serving, public render parameters, and more flexible inter-portlet communication. Portlets are implemented by various portal servers and can interoperate with standards like the Open Portlet Specification (and, in some cases, Web Services for Remote Portlets) to enable cross-vendor integration. Popular implementations include portal platforms like Liferay, IBM WebSphere Portal, Oracle WebCenter, and reference implementations such as Apache Pluto.

Usage: Portlets are commonly used to build customizable dashboards and intranet portals, where content from multiple applications is displayed together. They support user personalization, role-based access, and centralized navigation, enabling organizations to present a cohesive, modular web experience.