A portal is a collection of mini web applications, called portlets, which supports features like personalization, content aggregation, authentication and customization. Portlets act as windowed web applications within the portal and each window on a portal web page (called portal page) represents a portlet.
I don't think there is any hype left around portal or portlets anymore. Its more of a business decision to develop portals these days. The hype was around portlets when JSR 168 was released, but with time developers realized the shortcomings of the JSR 168 specification. Things were fixed in JSR -286 which is why we see now a more matured approach to developing portals using Java portlet technology.
The learning curve with portlet development will not be much, if you are using Portlets in Action book It does have its complexity because of the following reasons:
- multiple request processing phases (render, event, resource, action)
- portlets generate only HTML fragment and not the complete portal page
- minor differences in different portal servers implementation of Portlet 2.0 API
- lack of dedicated portlet frameworks for developing portlets - this is now addressed by Spring Portlet MVC - developing real-time portlets requires using servlets - meaning you need to secure servlets yourself. Chapter 12 example shows developing a real-time portlet using DWR Comet support.
- porting portlet applications to different portal servers is not as easy as porting web applications