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Chapter

f you come to servlets with a background in traditional Common Gate 

way Interface (CGI) programming, you are probably used to the idea of

I

 CGI variables.  These are a somewhat eclectic collection of informa 

tion about the current request. Some are based on the HTTP request line

and headers (e.g., form data), others are derived from the socket itself (e.g.,

the name and IP address of the requesting host), and still others are taken

from server installation parameters (e.g., the mapping of URLs to actual

paths). 

Although it probably makes more sense to think of different sources of

data (request data, server information, etc.) as distinct, experienced CGI pro 

grammers may find it useful to see the servlet equivalent of each of the CGI

variables. If you don't have a background in traditional CGI, first, count your

blessings; servlets are easier to use, more flexible and more efficient than

standard CGI. Second, just skim this chapter, noting the parts not directly

related to the incoming HTTP request. In particular, observe that you can

use 

getServletContext().getRealPath

 to map a URI (the part of the

URL that comes after the host and port) to an actual path and that you can

use 

request.getRemoteHost

 and 

request.getRemoteAddress

 to get the

name and IP address of the client.

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