Liferay provides 3 ways to extend the functionality of a Liferay portal. Each of the way fits is good for different needs.

Hook:

Liferay portal comes with a bundle where all the default built in portlets exist. Typically if any customization required in terms of JSP (UI) and portal properties. We need to go by Hook implementation. Hook is supported by hot deployment. Liferay documentation suggests that - Whenever possible, hooks should be used in place of EXT plugins, as they are hot-deployable and more forward compatible.

Some common scenarios that require the use of a hook are: 

• When you have to perform a custom action on portal startup
• When you have to perform a custom action on user login
• When you need to overwrite or extend portal JSPs
• When you need to modify portal properties
• When you need to replace a portal service with your own implementation.

EXT:

Liferay EXT Plugins are the most powerful way to extend the portal functionality. If any customization required in the core level classes then it can be done through EXT for example LDAP users and user groups IMPORT modification. but here in EXT, restart would be required.

EXT Plugins should be used only in case the portal functionality can not be extended using Portlet of Hooks. The EXT plugins are complex to develop and may cause maintenance issues in case you are trying to UPGRADE.

From liferay documents, The main use cases in which an Ext plugin may be used are:

• Customizations to portal.properties (that is not supported by Hook Plugins)
• Customizing and making changes to the Struts Actions for portal
• Customizations of the Liferay beans declared in Liferay's Spring files
• Adding JSPs that are referenced from portal properties that can only be changed from an ext plugin (be sure to check if the property can be modified from a hook plugin before doing this)
• Direct overwriting of a class (not recommended unless it's strictly necessary)

Portlet:

Portlets are the most common and easiest way to extend and provide a custom functionality for a liferay portal. This is a small application to fulfill the requirement of certain domain. It is basically a BUNCH of code(Java Files, JSP, CSS, Java Scripts etc.). Portlet is supported by hot deployment.

Liferay also has a marketplace where a lot of useful portlets are available for download and these portlets can contributed by anyone in the world. We recently contributed a Speed reading portlet and a My IP Address portlet in this marketplace for free use by liferay community. 

Liferay provides 3 ways to extend the functionality of a Liferay portal. Each of the way fits is good for different needs.

Hook:

Liferay portal comes with a bundle where all the default built in portlets exist. Typically if any customization required in terms of JSP (UI) and portal properties. We need to go by Hook implementation. Hook is supported by hot deployment. Liferay documentation suggests that - Whenever possible, hooks should be used in place of Ext plugins, as they are hot-deployable and more forward compatible.

Some common scenarios that require the use of a hook are: 

EXT:

Liferay EXT Plugins are the most powerful way to extend the portal functionality. If any customization required in the core level classes then it can be done through EXT for example LDAP users and user groups import modification. but here in EXT, restart would be required.

EXT Plugins should be used only in case the portal functionality can not be extended using Portlet of Hooks. The EXT plugins are complex to develop and may cause maintenance issues in case you are trying to upgrade.

From liferay documents, The main use cases in which an Ext plugin may be used are:

Portlet:

Portlets are the most common and easiest way to extend and provide a custom functionality for a liferay portal. This is a small application to fulfill the requirement of certain domain. It is basically a bunch of code(Java Files, JSP, CSS, Java Scripts etc.). Portlet is supported by hot deployment.

Liferay also has a marketplace where a lot of useful portlets are available for download and these portlets can contributed by anyone in the world. We recently contributed a Speed reading portlet and a My IP Address portlet in this marketplace for free use by liferay community.