A lot of these Java-based portals have plenty of open standards. A lot of JSR-### compliance.
From my perspective as a developer, I don't use the document sharing or publishing features of Liferay. My focus is on the portlet development. This means JSR-168 and JSR-286 portlet APIs.
I know nothing about SharePoint, so I can't really compare the two. I just know that I really dislike Java portlet development, and am ready to never have to do it again.
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