Datasheet

The Portlet Interface and the GenericPortlet

The Portlet interface defines the behaviors that all portlets must implement. Typically, you would pre-

fer to extend the

GenericPortlet class to build a portlet, because it provides structures for providing

all of the typical portlet implementation methods, not simply the required ones.

Portlet Life Cycle

Much like servlets, a portlet’s life cycle is managed by the container, and has an init method that is

used to manage the initialization requirements (creating resources, configuring, and so on). Portlets are

not guaranteed to be loaded until needed, unless you configure the container to load them on startup.

The

init method takes an object that implements the PortletConfig interface, which manages initial-

ization parameters and the portlet’s

ResourceBundle. This object can be used to get a reference to the

object that implements the

PortletContext interface.

Portlet developers don’t typically spend a lot of time worrying about the intricacies of portlet container

initialization exceptions, because generally they are thrown, and the developer reacts to them (debug-

ging the circumstance that led to the exception and correcting it if appropriate). However, it is worth

noting that an

UnavailableException is able to specify a time for which the portlet will be unavail-

able. This could be both useful (keeping the portlet container from continuously trying to load the port-

let) and aggravating (Why isn’t the portlet container reloading my portlet?!) to a developer.

The

destroy method provides the opportunity to clean up resources that were established in the init

method. This is analogous to the destroy method in a servlet, and is called once when the container

disposes of the portlet.

Portlet Runtime States

When a portlet is running, it has an associated Preferences object that allows for customization of the

portlet. The initial values of the preferences are those specified in the deployment descriptor, but the

portlet has full programmatic access to its preferences.

When a portlet is placed on a page, a

Preferences object is related to it. The pairing of the portlet and a

Preferences object on a page is known as a portlet window. A page can contain many of the same

portlet windows within its display.

Before you start wondering why all of these

Preferences objects are necessary, realize that this is pro-

viding the capability to perform a major features of a portal— customization. While the initial portlet

Preferences object is great for specifying the configuration and runtime state of the portlet, it is

When an exception is thrown in the portlet init method, the destroy method is

guaranteed not to be called. Therefore, if resources are created in the

init method

prior to the exception being thrown, the developer cannot expect the

destroy

method to clean them up, and must handle them in the exception’s catch block.

Chapter 1

04 469513 Ch01.qxd 1/16/04 11:04 AM Page 8