Prentice Hall and Sun Microsystems. Personal use only; do not redistribute.
5.1 Servlet Equivalent of CGI Variables
117
HTTP_XXX_YYY
Variables of the form 
HTTP_HEADER_NAME
 were how CGI programs 
obtained access to arbitrary HTTP request headers. The 
Cookie
 header 
became 
HTTP_COOKIE
, 
User Agent
 became 
HTTP_USER_AGENT
, 
Ref 
erer
 became 
HTTP_REFERER
, and so forth. Servlets should just use 
request.getHeader
 or one of the shortcut methods described in 
Chapter 4 (Handling the Client Request: HTTP Request Headers).
PATH_INFO
This variable supplies any path information attached to the URL after the 
address of the servlet but before the query data. For example, with 
http://host/servlet/coreservlets.SomeServ 
let/foo/bar?baz=quux
, the path information is 
/foo/bar
. Since serv 
lets, unlike standard CGI programs, can talk directly to the server, they 
don't need to treat path information specially. Path information could be 
sent as part of the regular form data and then translated by 
getServlet 
Context().getRealPath
. Access the value of 
PATH_INFO
 by using 
request.getPathInfo()
.
PATH_TRANSLATED
PATH_TRANSLATED
 gives the path information mapped to a real path on 
the server. Again, with servlets there is no need to have a special case for 
path information, since a servlet can call 
getServletContext().get 
RealPath
 to translate partial URLs into real paths. This translation is 
not possible with standard CGI because the CGI program runs entirely 
separately from the server. Access this variable by means of 
request.getPathTranslated()
.
QUERY_STRING
For 
GET
 requests, this variable gives the attached data as a single string 
with values still URL encoded. You rarely want the raw data in servlets; 
instead, use 
request.getParameter
 to access individual parameters, 
as described in Chapter 3 (Handling the Client Request: Form Data). 
However, if you do want the raw data, you can get it via 
request.getQueryString()
.
REMOTE_ADDR
This variable designates the IP address of the client that made the 
request, as a 
String
 (e.g., 
"198.137.241.30"
). Access it by calling 
request.getRemoteAddr()
.
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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