As an application grows in size, so will the number of action
mappings. Wildcards can be used to combine similar mappings into one
more generic mapping.
The best way to explain wildcards is to show an example and walk
through how it works. This example modifies a conventional mapping to
use wildcards to match all pages that start with /edit:
<!-- Generic edit* mapping -->
<action
name="/edit*"
class="org.apache.struts.webapp.example.Edit{1}Action">
<result
name="failure"
path="/mainMenu.jsp"/>
<result
path="/\{1\}.jsp"/>
</action>
The "*" in the path attribute allows the mapping to match the
request URIs /editSubscription, editRegistration, or any other URI that
starts with /edit, however /editSubscription/add would not be matched.
The part of the URI matched by the wildcard will then be substituted
into various attributes of the action mapping and its action results
replacing {1}. For the rest of the request, the framework will see the
action mapping and its action results containing the new values.
Mappings are matched against the request in the order they appear in
the framework's configuration file. If more than one pattern matches
the last one wins, so less specific patterns must appear before more
specific ones. However, if the request URL can be matched against a
path without any wildcards in it, no wildcard matching is performed and
order is not important.
Wildcard patterns can contain one or more of the following special tokens:
* Matches zero or more characters excluding the slash ('/') character.
** Matches zero or more characters including the slash ('/') character.
\character The backslash character is used as an escape sequence. Thus * matches the character asterisk ('*'), and
matches the character backslash ('
').
In the action mapping and action results, the wildcard-matched
values can be accessed with the token {N} where N is a number from 1 to
9 indicating which wildcard-matched value to substitute. The whole
request URI can be accessed with the {0} token.
Also, the action mapping properties (set using the <set-property
key="foo" value="bar"> syntax) will accept wildcard-matched strings
in their value attribute.
Like the action mapping, the action result properties (set using the
<set-property key="foo" value="bar"> syntax) will accept
wildcard-matched strings in their value attribute.
See also Wildcard Method