Prentice Hall and Sun Microsystems. Personal use only; do not redistribute.
104
Chapter 4 Handling the Client Request: HTTP Request Headers
check the 
Accept Encoding
 header. Admittedly, this is not always 
possible, but when it is not, you should ask yourself if the browser spe 
cific feature you are using really adds enough value to be worth the 
maintenance cost. 
Most Internet Explorer versions list a  Mozilla  (Netscape) version first 
in their 
User Agent
 line, with the real browser version listed paren 
thetically. This is done for compatibility with JavaScript, where the 
User Agent
 header is sometimes used to determine which JavaScript 
features are supported. Also note that this header can be easily spoofed, 
a fact that calls into question the reliability of sites that use this header 
to  show  market penetration of various browser versions. Hmm, mil 
lions of dollars in marketing money riding on statistics that could be 
skewed by a custom client written in less than an hour, and I should take 
those numbers as accurate ones?
Via
This header is set by gateways and proxies to show the intermediate 
sites the request passed through.
Warning
This rarely used catchall header lets clients warn about caching or con 
tent transformation errors.
4.4 Sending Compressed Web 
Pages
Several recent browsers know how to handle gzipped content, automatically
uncompressing documents that are marked with the 
Content Encoding
header and then treating the result as though it were the original document.
Sending such compressed content can be a real timesaver, since the time
required to compress the document on the server and then uncompress it on
the client is typically dwarfed by the savings in download time, especially
when dialup connections are used. 
Browsers that support content encoding include most versions of Netscape
for Unix, most versions of Internet Explorer for Windows, and Netscape 4.7
and later for Windows. Earlier Netscape versions on Windows and Internet
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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