This document lists all of the available selectors of Apache Cocoon and
describes their purpose.
You may also wish to read
Using and Implementing
Matchers and Selectors.
Selectors in Apache Cocoon have a role similar to matchers
with additional flexibility. If you haven't learned about
matchers yet, read about them here
before continuing. Selectors are designed to evaluate a
generally simple boolean expression regarding some
part of the environment (request URI, headers, or cookies, for example).
The result of this evaluation determines which pipeline fragments
should be combined within a given pipeline. Unlike matchers,
selectors can be active decision-driving components.
For example, a matcher makes only simple
"yes/no" decisions. If a match is successful, a
pipeline is executed. If not, it is ignored.
Selectors go further by allowing more complex, multiple-choice
use cases. In short, consider matchers to be simple "if"
statements. By extension, consider selectors to have all
the power of an "if-else if-else" or "switch-case" constructs.
The selector syntax should be familiar to anyone who
As an example, consider the typical scenario in which a page should
be rendered differently based on the client browser.
Given the large number and diversity of available browsers,
it would be awkward and counterintuitive to address this need
with a set of matchers. The BrowserSelector tests a given parameter
against the user-agent request header. Using this single selector,
we can deploy a consistent and readable setup.
The Selectors in Cocoon
<map:transform src="stylesheets/netscape.xsl" />
<map:transform src="stylesheets/ie.xsl" />
<map:transform src="stylesheets/text-based.xsl" />
<map:transform src="stylesheets/html.xsl" />
Available Selectors in Cocoon include the following:
BrowserSelector: matches the value of the "test"
parameter against the HTTP User-Agent header, allowing it to
recognize the browser issuing the request;
CodeSelector: matches a snippet of Java code
given as the "test" parameter against the environment;
HostSelector: matches the "test" parameter value
against the Host request header
ParameterSelector: matches the string specified
in the "test" parameter against a specified Cocoon internal
(e.g. sitemap) parameter;
HeaderSelector: same as the Parameter selector,
but matches against the request headers;
RequestSelector: again, same as the Parameter selector,
but matches against the Request parameters;
SessionSelector: finally, this selector is used as
the Parameter selector to match against an arbitrary session