Action Configuration

The action mappings are the basic "unit-of-work" in the framework. Essentially, the action maps an identifier to a handler class. When a request matches the action's name, the framework uses the mapping to determine how to process the request.

Action Mappings

The action mapping can specify a set of result types, a set of exception handlers, and an interceptor stack. But, only the name attribute is required. The other attributes can also be provided at package scope.

<action name="Logon" class="tutorial.Logon">
  <result type="redirect-action">Menu</result>
  <result name="input">/tutorial/Logon.jsp</result>
</action>

Action Names

In a web application, the name attribute is matched a part of the location requested by a browser (or other HTTP client). The framework will drop the host and application name and the extension, and match what's in the middle. So, a request for http://www.planetstruts.org/struts2-mailreader/Welcome.do will map to the Welcome action.

Within an application, the link to an action is usually generated by a Struts Tag. The tag can specify the action by name, and the framework will render the default extension and anything else that is needed.

<s:form action="Hello">
    <s:textfield label="Please enter your name" name="name"/>
    <s:submit/>
</s:form>

Action Methods

The default entry method to the handler class is defined by the Action interface.

public interface Action {
    public String execute() throws Exception;
}

Implementing the Action interface is optional. If Action is not implemented, the framework will use reflection to look for an execute method.

Sometimes, developers like to create more than one entry point to an Action. For example, in the case of of a data-access Action, a developer might want separate entry-points for create, retrieve, update, and delete. A different entry point can be specified by the method attribute.

<action name="delete" class="example.CrudAction" method="delete">

If there is no execute method, and no other method, specified in the configuration, the framework will throw an exception.

Wildcard Method

Many times, a set of action mappings will share a common pattern. For example, all your edit actions might start with the word "edit", and call the edit method on the Action class. The delete actions might use the same pattern, but call the delete method instead.

Rather than code a separate mapping for each action class that uses this pattern, you can write it once as a wildcard mapping.

<action name="*Crud" class="example.Crud" method="{1}">

Here, a reference to "editCrud" will call the edit method on an instance of the Crud Action class. Likewise, a reference to "deleteCrud" will call the delete method instead.

Another common approach is to postfix the method name and set it off with an exclamation point (aka "bang"), underscore, or other special character.

• "action=Crud_input"
• "action=Crud_delete"

To use a postfix wildcard, just move the asterisk and add an underscore.

<action name="Crud_*" class="example.Crud" method="{1}">

From the framework's perspective, a wildcard mapping creates a new "virtual" mapping with all the same attributes as a conventional, static mapping. As a result, you can use the expanded wildcard name as the name of validation, type conversion, and localization files, just as if it were an Action name (which it is!).

• Crud_input-validation.xml
• Crud_delete-conversion.xml

The postfix "!" notation is also available in WebWork 2, but it is implemented differently. To use the old implementation, set struts.enable.DynamicMethodInvocation=TRUE in the struts.properties file. To use wildcards instead (preferred), set struts.enable.DynamicMethodInvocation=FALSE.

ActionSupport Default

If the class attribute in an action mapping is left blank, the com.opensymphony.xwork.ActionSupport class is used as a default.

<action name="Hello">
   // ...
</action>

The ActionSupport class has execute and input methods that return "success".

Post-Back Default

A good practice is to link to actions rather than pages. Linking to actions encapsulates which server page renders, and ensures that an Action class can fire before a page renders.

Another common workflow stategy is to first render a page using an alternate method, like input and then have it submit back to the default execute method.

Using these two strategies together creates an opportunity to use a "post-back" form that doesn't specify an action. The form simply submits back to the action that created it.

<s:form>
    <s:textfield label="Please enter your name" name="name"/>
    <s:submit/>
</s:form>

Action Default

Usually, if an action is requested, and the framework can't map the request to an action name, the result will be the usual "404 - Page not found" error. But, if you would prefer that an ominbus action handle any unmatched requests, you can specify a default action. If no other action matches, the default action is used instead.

<package name="Hello" extends="action-default">

<default-action-ref name="UnderConstruction">

<action name="UnderConstruction">
  <result>/UnderConstruction.jsp</result>
</action>

There are no special requirements for the default action. Each package can have its own default action, but there should only be one default action per namespace.

Wildcard Default

Using wildcards is another approach to default actions. A wildcard action at the end of the configuration can be used to catch unmatched references.

<action name="*" >
  <result>/(1).jsp</result>
</action>

When a new action is needed, just add a stub page.

FAQ

How can we display dynamic or static images that can be provided as an array of bytes?
How can we test Actions?
How can we force the Action Mappings (struts.xml) to reload?