difference between hook and ext

Hook                                                          EXT

Hot Deployable                                                    Not Hot Deployable

No need to Restart the server                              Need to restart the server

Maintenance is Easy                                           Maintenance is difficult

Not overriding code directly                                It will replace the code directly

Undoing is easy                                                   Undoing is difficult

Note : We can deploy only one ext plugin per Liferay installation.

Key Point : To avoid multiple submit in form submission when it got refresh give the below line in  liferay-portlet.xml

<action-url-redirect>true</action-url-redirect>