Why to use PortletURL? - liferay

Question

This thread is not a question , it was a doubt raised when I was going through Liferay Forums about using PortletURL.
In some cases I see this PortletURL inside the javscript Method
function createRowURL() {
var portletURL = new Liferay.PortletURL();
portletURL.setParameter("rowNumber", "25" );
return portletURL.toString();
}
In some cases I see this PortletURL inside the doView Method as shown
To get currentURL :
PortletURL url = PortletURLUtil.getCurrent(renderRequest, mimeResponse or renderResponse)
creating PortletURL from renderResponse :
For RenderURL:
PortletURL renderURL = renderResponse.createRenderURL();
For actionURL:
PortletURL actionURL = renderResponse.createActionURL();
Could anybody please tell me in which case PortletURL would be useful ?

Answer 1

Portlet applications are different from normal web applications. Portlets are mini pages inside a parent page called a portal and multiple portals become a book (a Weblogic term). Normal URL will not work in this situation. Aside from the reason given above, a portlet has a life circle with different states. You have to give the Portlet container a way to determine which portlet is communicating with it and what state it is being in - such as the window state of the portlet - is it minimized, maximized, or normal. Of course, another important function of the PortletUrl is to carry request parameters. If you are looking at a PortletURL you will sure see a lot exotic names along with the request parameters you give it.
Although most of the information needed by a PortletURL are common in many situations, the structure of a PortletURL is implementation-dependent and it is generated by the Portlet container one way or the other. There has been some time since my last liferay experience. I never used liferay specific javascript in my application. I used my own javascript/ajax to communication with the portal container. So I am just guessing the javascript way you presented is also liferay specific and won't be portable among different portal frameworks.
Edit: added types of PortletURLs and their differences and usage following comment from #PrakashK.
There are two types of PortletURLs:
Action URLs, they trigger an action request followed by a render request.
Render URLs, they trigger a render request.
So the purpose of an ActionURL is to trigger some kind of action - such as pressing a button. The action request will be intercepted by portlet container and send to appropriate action request handlers which process the action request and set necessary render parameters to be used by the render phase. In the life cycle of a portlet, a render request ALWAYS follows an action request. On the other hand, a RenderURl, as it's name suggested, is mainly for rendering the portlet.
Because of the "rendering" nature of a RenderURL, in JSR168(Portlet 1.0), you could not serve dynamically generated resources directly through the portlet. The only workaround is to use an additional servlet to serve the resources. The biggest problem of this approach is the inability of a Servlet to be involved in the lifecycle of a portlet. Direct links to the resources in the same portlet web application are not guaranteed to pass through the portal server and will not have portlet context available. To overcome this, in JSR286(Portlet 2.0), a feature called resource serving and a new kind of URL called ResourceURL has been introduced to enable a portlet to dynamically serve a resource. ResourceURL is not a PortletURL although they extend the same BaseURL. The biggest difference between a ResourceURL and an ActionURL is that a ResourceURL will NOT trigger a render request. This makes possible an Ajax request to the resource.
For more information on Portlet 2.0, please refer to [JSR286].
Hope the above information would be useful to you.