Action Configuration

Versions Compared

Key

  • This line was added.
  • This line was removed.
  • Formatting was changed.

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.

Table of Contents
minLevel2

Action Mappings

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

Code Block
titleA Logon Action

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

...

Code Block
titleA Hello Form

<s:form action="Hello">
    <s:textfield label="Please enter your name" name="name"/>
    <s:submit/>
</s:form>
Info
titleAction Names With Slashes

If your action names have slashes in them (for example, <action name="admin/home" class="tutorial.Admin"/>) you need to specifically allow slashes in your action names via a constant in the struts.xml file by specifying <constant name="struts.enable.SlashesInActionNames" value="true"/>. See JIRA Issue WW-1383 for discussion as there are side effects to setting this property to true.

...

Code Block
titleAction interface

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

...

Sometimes, developers like to create more than one entry point to an Action. For example, in the case 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.

Code Block
xml

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

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

excerptDefaultActionInvocation will try to call also doDelete if it couldn't find delete method in action's class.

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.

Code Block
xml

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

...

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

Code Block
xml

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

...

!" in the action name, the Wildcard Method will overlap with another flexible approach to mapping, <ac:link ac:anchor="Dynamic Method Invocation"><ac:link-body>Dynamic Method Invocation</ac:link-body></ac:link>. To use action names that include the "!" character, set struts.enable.DynamicMethodInvocation to FALSE in the application configuration.

Warning

If Wildcard Method mapping uses a "

Wiki Markup

...

The Wildcard Method feature is implemented differently. When a Wildcard Method action is invoked, the framework acts as if the matching action had been hardcoded in the configuration. The framework "believes" it's executing the action Category!create and "knows" it is executing the create method of the corresponding Action class. Accordingly, we can add for a Wildcard Method action mapping its own validations, message resources, and type converters, just like a conventional action mapping. For this reason, the Wildcard Method is preferred.

In Struts 2.3, an option was added to restrict the methods that DMI can invoke. First, set the attribute strict-method-invocation="true" on your <package> element. This tells Struts to reject any method that is not explicitly allowed via either the method attribute (including wildcards) or the <allowed-methods> tag. Then specify <allowed-methods> as a comma-separated list of method names in your <action>. (If you specify a method attribute for your action, you do not need to list it in <allowed-methods>.)

Note that you can specify <allowed-methods> even without strict-method-invocation. This restricts access only for the specific actions that have <allowed-methods>.

Code Block
xml
titleExample struts.xml
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE struts PUBLIC
	"-//Apache Software Foundation//DTD Struts Configuration 2.3//EN"
	"http://struts.apache.org/dtds/struts-2.3.dtd">
<struts>

  <constant name="struts.enable.DynamicMethodInvocation" value="true"/>

  <package name="default" extends="struts-default" strict-method-invocation="true">

	<action name="index" class="org.apache.struts2.examples.actions.Index">
		<result name="success" type="redirectAction">hello</result>
	</action>

	<action name="hello" class="org.apache.struts2.examples.actions.HelloAction">
		<result name="success">/WEB-INF/content/hello.jsp</result>
		<result name="redisplay" type="redirectAction">hello</result>
		<allowed-methods>add</allowed-methods>
	</action>

  </package>
</struts>
Warning

Strict DMI doesn't work with the Convention Plugin yet!

ActionSupport Default

If the class attribute in an action mapping is left blank, the com.opensymphony.xwork2.ActionSupport class is used as a default.

Code Block

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

...

Code Block
titlePosting Back

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

...

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 omnibus action handle any unmatched requests, you can specify a default action. If no other action matches, the default action is used instead.

Code Block
xml

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

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

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

    ...

...

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

Code Block
xml

<action name="*">
  <result>/{1}.jsp</result>
</action>

...

(warning) It's important to put a "catchall" wildcard mapping like this at the end of your configuration so it won't attempt to map every request!

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?

Next: Wildcard Mappings