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Wildcards

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.

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Also, the action mapping and 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

Parameters in namespaces

From Struts 2.1+ namespace patterns can be extracted as request parameters and bound to the action. To enable this feature, set the following constant in struts.xml:

<constant name="struts.patternMatcher" value="named-variable"/>

With that in place, namespace definitions can contain {PARAM_NAME} patterns which will be evaluated against the request URL and extracted as parameters, for example:

@Namespace{"/users/{userID}");
public class DetailsAction exends ActionSupport {
  private Long userID;
  public void setUserID(Long userID) {...}
}

If the request URL is /users/10/detail, then the DetailsAction will be executed and its userID field will be set to 10.

Only one PatternMatcher implementation can be used at a time.  The two implementations included with Struts 2 are mutually exclusive.  You cannot use Wildcards and Named Variable patterns at the same application (if that were required, you'd need to create a custom PatternMatcher implementation).

Some tags tags not are 100% compatible with variables in the namespace. For instance, they may write the literal namespace into the HTML (eg /{user}/2w) instead of the path used in the request (ie. /brett/24).  This usually affects attributes that attempt to guess the namespace of an action (eg. Form tag, Action tag, action=). This problem can be avoided by using HTML tags directly with relative paths or explicit URLs.

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