Extension

The Extension Environment allows for complete customization of Liferay.

• Internal portlets can be modified. 
• Liferay's .jsp pages can be changed. 
• Customizations are kept separate from the Liferay source. 
• The Liferay source code does not have to be modified.
• Developers have a clear upgrade path. 
• The combination of the MIT license and the extension environment means that organization-specific customizations do not need to be contributed back to the Liferay project.

Plugins

The Plugins SDK is a simple environment for the development of Liferay plugins.

•  Portlet, theme and layout development used to take place in the ext environment. 
• The ext environment no longer supports portlet and theme development, except for struts portlets and modifying/extending Liferay’s out-of-the-box portlets. 
• The Plugins SDK is to be used instead to create hot-deployable portlets, themes and layouts.

Portlets can make use of any application framework that Liferay supports 

• Struts 
• JSF 
• Spring 
• JSP
• MVC