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Chapter 5 Accessing the Standard CGI Variables

5.1 Servlet Equivalent of CGI 

Variables

For each standard CGI variable, this section summarizes its purpose and the

means of accessing it from a servlet. As usual, once you are familiar with this

information, you may want to use Appendix A (Servlet and JSP Quick

Reference) as a reminder. Assume 

request

 is the 

HttpServletRequest

supplied to the 

doGet

 and 

doPost

 methods.

AUTH_TYPE

If an 

Authorization

 header was supplied, this variable gives the 

scheme specified (

basic

 or 

digest

). Access it with 

request.getAu 

thType()

.

CONTENT_LENGTH

For 

POST

 requests only, this variable stores the number of bytes of data 

sent, as given by the 

Content Length

 request header. Technically, 

since the 

CONTENT_LENGTH

 CGI variable is a string, the servlet 

equivalent is

 String.valueOf(request.getContentLength())

 or 

request.getHeader("Content Length")

. You ll probably want to 

just call

 request.getContentLength()

, which returns an 

int

. 

CONTENT_TYPE

CONTENT_TYPE

 designates the MIME type of attached data, if specified. 

See Table 7.1 in Section 7.2 (HTTP 1.1 Response Headers and Their 

Meaning) for the names and meanings of the common MIME types. 

Access 

CONTENT_TYPE

 with 

request.getContentType()

.

 DOCUMENT_ROOT

The 

DOCUMENT_ROOT

 variable specifies the real directory corresponding 

to the URL 

http://host/

. Access it with 

getServletContext().getRealPath("/")

. In older servlet specifica 

tions you accessed this variable with 

request.getRealPath("/")

; the 

older access method is no longer supported. Also, you can use 

get 

ServletContext().getRealPath

 to map an arbitrary URI (i.e., URL 

suffix that comes after the hostname and port) to an actual path on the 

local machine.

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

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