Prentice Hall and Sun Microsystems. Personal use only; do not redistribute.

4.4 Sending Compressed Web Pages

105

DILBERT reprinted by permission of United Syndicate, Inc.

Explorer on non Windows platforms generally do not support content encod 

ing. Fortunately, browsers that support this feature indicate that they do so

by setting the 

Accept Encoding

 request header. Listing 4.2 shows a servlet

that checks this header, sending a compressed Web page to clients that sup 

port gzip encoding and sending a regular Web page to those that don't. The

result showed a tenfold speedup for the compressed page when a dialup con 

nection was used. In repeated tests with Netscape 4.7 and Internet Explorer

5.0 on a 28.8K modem connection, the compressed page averaged less than 5

seconds to completely download, whereas the uncompressed page consis 

tently took more than 50 seconds.

Core Tip

Gzip compression can dramatically reduce the download time of long text 

pages.

Implementing compression is straightforward since gzip format is built in

to the Java programming languages via classes in 

java.util.zip

. The serv 

let first checks the 

Accept Encoding

 header to see if it contains an entry for

gzip. If so, it uses a 

GZIPOutputStream

 to generate the page, specifying

gzip

 as the value of the 

Content Encoding

 header. You must explicitly call

close

 when using a 

GZIPOutputStream

. If gzip is not supported, the servlet

uses the normal 

PrintWriter

 to send the page. To make it easy to create

benchmarks with a single browser, I also added a feature whereby compres 

sion could be suppressed by including 

?encoding=none

 at the end of the

URL. 

Second edition of this book: www.coreservlets.com; Sequel: www.moreservlets.com.

Servlet and JSP training courses by book's author: courses.coreservlets.com.