WHAT IS PORTLET?

Portlets:

Similar to servlets, portlets are web components that are deployed inside of a container and generate dynamic content. On the technical side, a portlet is a class that implements the javax.portlet.Portlet interface and is packaged and deployed as a .war file inside of a portlet container.

Portlets are similar to servlets, in that:

1. Portlets are managed by a specialized container.
2. Portlets generate dynamic content.
3. A portlet's life cycle is managed by the container.
4. Portlets interact with web client via a request/response paradigm.

Portlets are different from servlets, in that:

1. Portlets only generate markup fragments, not complete documents.
2. Portlets are not directly URL addressable. You can’t send somebody URL of a portlet. You can send him the URL of the page containing a portlet.
3. Portlets cannot generate arbitrary content, since the content generated by a portlet is going to be part of portal page. If a portal server is asking for html/text, then all portlets should generate text/html content. On the other hand, if the portal server is asking for WML, then each portlet should generate WML content.

Portlet interface:

The Portlet interface is used by the portlet container to invoke the portlets. Every portlet has to implement this interface, either by directly implementing it, or by using an existing class implementing the Portlet interface.

A portlet is a Java technology-based web component. It is managed by the portlet container and processes requests and generates dynamic content as response. Portlets are used by portals as pluggable user interface components.

The content generated by a portlet is called a fragment. A fragment is a piece of markup (e.g. HTML, XHTML, WML) adhering to certain rules and can be aggregated with other fragments into a complete document. The content of a portlet is normally aggregated with the content of other portlets into the portal page.

The portlet container instantiates portlets manages their lifecycle and invoking them to process requests. The lifecycle consists of:

• initializing the portlet using using the init method
• request processsing
• taking the portlet out of service using the destroy method

Request processing is divided into two types:

• action requests handled through the processAction method, to perform actions targeted to the portlet

render requests handled through the render method, to perform the render operation

public void init(PortletConfig config)throws PortletException :

Called by the portlet container to indicate to a portlet that the portlet is being placed into service.

The portlet container calls the init method exactly once after instantiating the portlet. The init method must complete successfully before the portlet can receive any requests.

The portlet container cannot place the portlet into service if the init method

1.      Throws a PortletException

2.      Does not return within a time period defined by the portlet container

public void processAction(ActionRequest request,ActionResponse response)             throws PortletException,java.IOException

Called by the portlet container to allow the portlet to process an action request. This method is called if the client request was originated by a URL created (by the portlet) with the RenderResponse.createActionURL() method.

Typically, in response to an action request, a portlet updates state based on the information sent in the action request parameters. In an action the portlet may:

·         issue a redirect

·         change its window state

·         change its portlet mode

·         modify its persistent state

·         set render parameters

A client request triggered by an action URL translates into one action request and many render requests, one per portlet in the portal page. The action processing must be finished before the render requests can be issued.

public void render (RenderRequest request,   RenderResponse response)throws PortletException,java.io.IOException

Called by the portlet container to allow the portlet to generate the content of the response based on its current state.

public  void destroy():

Called by the portlet container to indicate to a portlet that the portlet is being taken out of service. Before the portlet container calls the destroy method, it should allow any threads that are currently processing requests within the portlet object to complete execution. To avoid waiting forever, the portlet container can optionally wait for a predefined time before destroying the portlet object.

This method enables the portlet to do the following:

·         clean up any resources that it holds (for example, memory, file handles, threads)

·         make sure that any persistent state is synchronized with the portlet current state in memory.