Cita:
Second, since the output of the servlet does not change except when the server is rebooted, init also stores a page modification date that is used by the getLastModified method. This method should return a modification time expressed in miliseconds since 1970, as is standard with Java dates. The time is automatically converted to a date in GMT appropriate for the Last-Modified header. More importantly, if the server receives a conditional GET request (one specifying that the client only wants pages marked If-Modified-Since a particular date), the system compares the specified date to that returned by getLastModified, returning the page only if it has been changed after the specified date. Browsers frequently make these conditional requests for pages stored in their caches, so supporting conditional requests helps your users (they get faster results) and reduces server load (you send fewer complete documents). Since the Last-Modified and If-Modified-Since headers use only whole seconds, the getLastModified method should round times down to the nearest second.
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