Question of properties file

[木叶清风-谢]

hi!I meet a problem about the properties files.
I discover that the properties won't be loaded automatically unless use  
<constant name="struts.custom.i18n.resources" value="global,Register,Package"/> 
in struts.xml.
I want to know how to configure the struts2 to load Package.properties and 
(activity_name).properties automatically,notice the <constant 
name="struts.devMode" value="true" />,the value is true!!!‍