Question

can i access ApplicationResource.properties file keys from Action Class in Struts 2
and update the values of the key ?

Answer 1

I don’t think you can update the values of those keys directly, that would kind of defeat the purpose of it being (static) resources.
You can however use placeholders.

ApplicationResources.properties

property.key=Hi {0}, there's a problem with {1}

MyAction.java

public ActionForward execute(ActionMapping mapping,
                             ActionForm form,
                             javax.servlet.ServletRequest request,
                             javax.servlet.ServletResponse response)
                      throws java.lang.Exception {
MessageResources msgResource = getResources(request);
String msg = msgResource.getMessage("property.key", "Sankar", "updating values in the resources.");
}