Question

It is not clear to me when is a Portlet‘s init method called. Is it called when the container instantiated or when a first request to the portlet comes?
Does it have the same behavior as the Servlet#init?

Answer 1

It depends on the container. From the Portlet 2.0 spec:

PLT.5.2.1 Loading and Instantiation

The portlet container is responsible for loading and instantiating
portlets. The loading and instantiation can occur when the portlet
container starts the portlet application, or delayed until the portlet
container determines the portlet is needed to service a request.

…

PLT.5.2.2 Initialization

After the portlet object is instantiated, the
portlet container must initialize the portlet before invoking it to
handle requests.