what is the use of Activator.java in CQ ?

Symptoms

A change was made to a component by an author. The page need to be refreshed in order to immediately reflect the change. Is there a way to automate this such that the author does not need to refresh the page?

Resolution

The cq:listeners [cq:EditListenersConfig] is used to refresh the HTML page after a certain action is performed on a component. The cq:listeners node should be located as shown: 

/component-name [cq:Component]

   /cq:editConfig [cq:editConfig]

      /cq:listeners [cq:EditListenersConfig]

NOTE: Text in the "[]" is the nodetype. Text after "/" is the node name -- should be extact name except for the "component-name".

The following properties are associated with cq:listeners node are:

aftercreate

afterdelete

afteredit

afterinsert

aftermove

afterremove

There are three possible values that can be assigned to the properties above -- either "REFRESH_SELF", "REFRESH_PARENT", "REFRESH_PAGE".

So, if you want your text component to cause a page refresh after each edit, you would create the following structure:

...

/mytextcomponent [cq:Component]

   /cq:editConfig [cq:editConfig]

      /cq:listeners [cq:EditListenersConfig]

         - afteredit {REFRESH_PAGE}             <= property {value}

   mytextcomponent.jsp                          <= code

Refer:

http://helpx.adobe.com/experience-manager/kb/RefreshPageWhenModifyDialog.html