why did you specify particularly to use Head method ?
This places a lot of emphasis on using the HTTP methods strictly according to the intent of the HTTP specifiction. HEAD is intended to get "metadata" about a resource, such as the last modified time.
Since the HttpServlet base class already contains doXXX methods for all of the HTTP methods, adding a doHead method to your custom servlet is simple.
Wrt Bill'statement pertaining to HEAD method is correct :
HEAD method can be used for obtaining metainformation about the entity implied by the request without transferring the entity-body itself.
This method is often used for testing hypertext links for validity, accessibility, and recent modification.
But how come it will be useful in finding/knowing that there is change in the backend.
May be I am wrong in understanding, when saying/considering backend as DATABASE resource.
Otherwise whatever William said is right and I go with that.