Prentice Hall and Sun Microsystems. Personal use only; do not redistribute.
2.8 An Example Using Servlet Initialization and Page Modification Dates
45
Figure 2 8
Output of LotteryNumbers servlet.
with Java dates. The time is automatically converted to a date in GMT appro 
priate 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
, only returning the page
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 as well as reducing server load. Since the 
Last Mod 
ified
 and 
If Modified Since
 headers use only whole seconds, the 
get 
LastModified
 method should round times down to the nearest second. 
Figures 2 9 and 2 10 show the result of requests for the same servlet with
two slightly different 
If Modified Since
 dates. To set the request headers
and see the response headers, I used 
WebClient
, a Java application shown in
Section 2.10 (WebClient: Talking to Web Servers Interactively) that lets you
interactively set up HTTP requests, submit them, and see the results.
Second edition of this book: www.coreservlets.com; Sequel: www.moreservlets.com.
Servlet and JSP training courses by book's author: courses.coreservlets.com.






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