Is it possible to create a few portlets inside a portlet? I mean a multilevel portlet.
Yes. You can use the Nested Portlet to this purpose. This is a layout container for other portlets. You can choose the wanted layout in the configuration.
Yes, definately, you can have portlet within portlet.
Liferay provides taglib, thru which you can easily embed different util portlets (web content display, breadcrumb, navigation etc) within portlet
NESTED-PORTLET
Assuming that you are talking about a framework, a platform or something similar, yes, it's possible. Look if your framework have a kind of Nested-portlet. I'm using the liferay platform, and they offer an implementation of Nested Portlet.
No you can't have portlet within portlet, its similar to having servlet within servlet...
来源：https://stackoverflow.com/questions/3101247/liferay-portlets-inside-portlet