[S2]Could not find or error in struts.properties

[WongTseng]

I am a newbie to Strus2, and I have just set up a Struts2 project of blank
example. When I start the web container, it throws an exception.

java.lang.IllegalStateException: struts.properties missing
   at org.apache.struts2.config.PropertiesSettings.<init>(
PropertiesSettings.java:49)
   at org.apache.struts2.config.DefaultSettings.<init>(DefaultSettings.java
:52)

the directory structure is as follow:
WEB-INF
    |----web.xml
    |----struts.properties
    |----applicationContext.xml
    |----class
    |        |----struts.xml
    |        |----example.xml
    |----example
             |----Login-validation.xml
             |----package.properties
             |----package_es.properties

I just don't know where these xml files should be correctly located. The
struts2 is rather webwork than Struts,so don't know how  to deal with it.
Any help is userful to me.
--
Wong Tseng
王曾