Java Portlet Specification

A Java Portlet Specification defines a contract between portlets and their containers; they provides a convenient programming model for Java portlet developers. It is defined through various Java Specification Requests (JSRs).

Portlets
A portlet is a pluggable user interface software component that is managed and displayed in a web portal. A portlet responds to requests from a web client with and generates dynamic content. Some examples of portlet applications are e-mail, weather reports, discussion forums, and news.

Portlet containers
A portlet is managed by a portlet container, which runs portlets and provides them with the required runtime environment. A portlet container receives requests from the portal to execute requests on the portlets hosted by it.

Specifications
Portlet standards are platform independent application programming interfaces that are intended to enable software developers to create portlets that can be plugged into any portal supporting the standards. An example is the Java Portlet Specification. A Java portlet resembles a Java Servlet, but produces fragments rather than complete documents, and is not bound by a URL. A Java Portlet Specification (JSR) defines a contract between portlets and the portlet container. JSRs provides a convenient programming model for Java portlet developers.

JSR 168
The Java Portlet Specification V1.0 was developed under the Java Community Process as Java Specification Request JSR 168, and released in its final form in October 2003.

The Java Portlet Specification V1.0 introduces the basic portlet programming model with:
 * two phases of action processing and rendering in order to support the Model–View–Controller pattern.
 * portlet modes, enabling the portal to advise the portlet what task it should perform and what content it should generate
 * window states, indicating the amount of portal page space that will be assigned to the content generated by the portlet
 * portlet data model, allowing the portlet to store view information in the render parameters, session related information in the portlet session and per user persistent data in the portlet preferences
 * a packaging format in order to group different portlets and other Java EE artifacts needed by these portlets into one portlet application which can be deployed on the portal server.
 * Portal development as a way to integrate the different web-based applications for supporting deliveries of information and services.

Portlet Catalog

 * Initially Java portal vendors had their own portlet development framework thus those portlets were confined to specific portal servers and couldn't be deployed to the rest of the Java portals. After JSR 168 inception, Java portlets may be deployed on any Java portal servers adhering to JSR 168 specifications.
 * A Portlets Catalog is a set of portlets that are ready-to-use components for enterprise portals. For those who want to adopt portals certainly need many and variety of portlets to deploy and run. Here Portlets catalog are of use.
 * A JSR 168 portlets catalog makes sure that portlets under this catalog may run on any standards–compliant Java portal server. Types of portlet solution (vertical domains and technology) like collaboration, social networking, community, content management, utility, calendaring, HRM all are available in these catalogs.
 * There are many open source and commercial Portlets Catalog available but JSR 168 based solutions are rare.
 * JSR 168 specifications offer suitability to the developers to reuse the code to maintain a set of JSR 168 compliant portlets. For deployers, it's easy to keep a single set of solution and deploy it on many.

JSR 286
JSR-286 is the Java Portlet Specification v2.0 as developed under the JCP and created in alignment with the updated version 2.0 of WSRP. It was released in June 2008. It was developed to improve on the short-comings of the version 1.0 specification, JSR-168. Some of its major features include:
 * Inter-Portlet Communication through events and public render parameters
 * Serving dynamically generated resources directly through portlets
 * Serving AJAX or JSON data directly through portlets
 * Introduction of portlet filters and listeners

JSR 362
JSR-362 is the Java Portlet Specification v3.0 and was released in April 2017. Some of its major features include:
 * Resource Dependencies
 * Explicit Render State
 * CDI 1.2 Integration
 * Servlet 3.1 Alignment
 * Portlet Hub & XHR IPC
 * FacesBridge Integration via JSR 378