The
meaning of this method is to return the last time the resource represented by the
servlet was modified. For example, if a GET for this servlet would return the contents of a file, you would override getLastModified() to return the modification date of the file. That way, browsers and proxies can find out whether they can use their own cached copy of the URL contents or have to download a new updated copy.
The
default implementation of this method simply returns a negative number (-1 in fact), which should tell proxies and browsers never to cache the page (Microsoft Proxy is another story altogether though). After all, as far as the HttpServlet class knows you may be generating different content in doGet/doPost for every request, so it cannot make smart assumptions about how long content will remain valid for.
Overriding this method with something sensible will reduce network traffic and improve your site's responsiveness.
- Peter