Namespace Configuration
The namespace attribute subdivides action configurations into logical modules, each with its own identifying prefix. Namespaces avoid conflicts between action names. Each namespace can have its own “menu” or “help” action, each with its own implementation. While the prefix appears in the browser URI, the tags are “namespace aware”, so the namespace prefix does not need to be embedded in forms and links.
Struts 2 Namespaces are the equivalent of Struts Action 1 modules, but more convenient and flexible.
Default Namespace
The default namespace is ""
- an empty string. The default namespace is used as a “catch-all” namespace. If an action
configuration is not found in a specified namespace, the default namespace is also be searched. The local/global
strategy allows an application to have global action configurations outside of the action element “extends” hierarchy.
The namespace prefix can be registered with Java declarative security, to ensure only authorized users can access the actions in a given namespace.
Root Namespace
A root namespace "/"
is also supported. The root is the namespace when a request directly under the context path is
received. As with other namespaces, it will fall back to the default ""
namespace if a local action is not found.
Namespace Example
<package name="default">
<action name="foo" class="mypackage.simpleAction">
<result name="success" type="dispatcher">greeting.jsp</result>
</action>
<action name="bar" class="mypackage.simpleAction">
<result name="success" type="dispatcher">bar1.jsp</result>
</action>
</package>
<package name="mypackage1" namespace="/">
<action name="moo" class="mypackage.simpleAction">
<result name="success" type="dispatcher">moo.jsp</result>
</action>
</package>
<package name="mypackage2" namespace="/barspace">
<action name="bar" class="mypackage.simpleAction">
<result name="success" type="dispatcher">bar2.jsp</result>
</action>
</package>
How the Code Works
If a request for /barspace/bar.action
is made, the /barspace
namespace is searched for the bar
action.
If found, the bar
action is executed, else it will fall back to the default namespace. In the Namespace Example,
the bar
action does exist in the /barspace
namespace, so the bar
action will be executed, and if “success” is
returned, the request will be forwarded to bar2.jsp
.
If a request is made to /barspace/foo.action
, the namespace /barspace
will be checked for action foo
.
If a local action is not found, the default namespace is checked. In the Namespace Example, there is no action foo
in the namespace /barspace
, therefore the default will be checked and /foo.action
will be executed.
In the Namespace Example, if a request for moo.action
is made, the root namespace "/"
is searched for a moo
action; if a root action is not found, the default namespace is checked. In this case, the moo
action does exist
and will be executed. Upon success, the request would be forwarded to moo.jsp
.
If a request is made for /foo.action
, the root "/"
namespace will be checked. If foo
is found, the root action
will be selected. Otherwise, the framework will check the default namespace. In the Namespace Example, the foo
action
does not exist in the root namespace, so the default namespace is checked, and the default foo action is executed.
Namespace are not hierarchical like a file system path. There is one namespace level. For example if the URL
/barspace/myspace/bar.action
is requested, the framework will first look for namespace /barspace/myspace
.
If the action does not exist at /barspace/myspace
, the search will immediately fall back to the default namespace ""
.
The framework will not parse the namespace into a series of “folders”. In the Namespace Example, the bar action
in the default namespace would be selected.