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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.