Do portlets have url that I can link directly?
I find some information says that portlets are not directly URL addressable.
But in JSR-286 , there are a topic about portlet url.
I want to know that if a portlet can be linked by a URL that I can send some parameter to it via http request.
That is one thing you can't do: direct linking to a portlet. Portlets are not like Servlets.
The URL for a portlet is not specified in web.xml as in case of Servlets. The portlet URL is not specified by the developer but created using methods defined in the RenderResponse object or by using the portletURL tag of portlet tag library. The Portlet URL chapter that you saw in the 2.0 spec, it deals with the different types of portlet URLs that you can create for a portlet to send it different types of requests, like RenderRequest, ActionRequest and ResourceRequest. Instead of directly linking to a portlet, you should link to a portal page, which contains the portlet.