AB Infinity feb 2014 | Página 3

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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.getAuthType().
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 specifications you accessed this variable with request.getRealPath("/"); the
older access method is no longer supported. Also, you can use getServletContext().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.
Servlet and JSP training courses by book’s author: courses.coreservlets.com.