Java Reference
In-Depth Information
jpeg or image
/
gif for other images.
MIME
types also exist for
XML
, multime-
dia, and applications.
A
POST
request instructs the server to execute an application to process a
block of information. A
POST
request can be issued within
HTML
to send
user-specified form data to the server for processing. The server then pro-
cesses the request and sends back a response, as in the
GET
. The traditional
method for processing the request is the Common Gateway Interface (
CGI
)
command.
CGI
simply starts a program on the server on behalf of the client.
This architecture can result in poor performance, because each request starts
a process, makes any required enterprise connections, processes the request,
takes down the connection, and then kills the process—an extraordinarily
cycle-expensive process. A significant advance over
CGI
, and the application
architecture for Java that we will use in this topic, is called a
servlet
. A Java
servlet is a Java program that stays resident after use. Chapter 3 will begin to
describe some antipatterns of servlet architectures.
2.2.6
HTML and XML
We have been working our way up the food chain to progressively higher level
layers.
HTML
was originally created as a standard way to format documents
for display, but it has grown to be rich enough to build basic application user
interfaces. Though there are many extensions and versions, its user interfaces
can be flexible, portable, scalable, and efficient.
HTML
consists of plain text,
marked up with tags. Known as
metadata
, or data about data, these tags
define how
HTML
documents are interpreted and rendered.
Where
HTML
tags attach a structure and meaning to documents,
XML
attaches structure and meaning to generic data. With
XML
, standard types can
be built to do many different things. Hundreds of
XML
standards already
exist.
XML
types can be used in a number of ways.
XML
documents can be
translated with Extensible Stylesheet Language (
XSL
). This translation tech-
nology can generate
HTML
from
XML
for easy presentation; it can even
repur-
pose
data, or translate content from one
XML
form to another. Within an
application, the Document Object Model (
DOM
) interface can be used to
parse even the most complex
XML
documents. You can find additional infor-
Numerous other great websites and books on
XML
are available as well.
Internet layers solve client/server problems
Each successive Internet standard forms an increasingly abstract software
layer. The combination that is the Internet has shown incredible power and