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Alias Interceptor

The aim of this Interceptor is to alias a named parameter to a different named parameter. By acting as the glue between actions sharing similar parameters (but with different names), it can help greatly with action chaining.

Action’s alias expressions should be in the form of #{ "name1" : "alias1", "name2" : "alias2" }. This means that assuming an action (or something else in the stack) has a value for the expression named name1 and the action this interceptor is applied to has a setter named alias1, alias1 will be set with the value from name1.

Parameters

Ordering relative to the params interceptor

The interceptor sets the aliased property on the action at the moment it runs, and so does the params interceptor. When a request carries both the source name and the target name, whichever of the two interceptors runs last wins:

Stack order Request foo=1&bar=2, aliases #{ 'foo' : 'bar' } bar after both have run
alias before params (the defaultStack order) alias sets bar=1, then params sets bar=2 2 — the directly submitted parameter wins
params before alias params sets bar=2, then alias sets bar=1 1 — the alias overrides the submitted parameter

To make the alias override a directly submitted parameter, place alias after params in a custom stack. Keep it before conversionError so that a conversion failure while binding the aliased property still becomes a field error:

<interceptor-stack name="aliasOverridesStack">
    <interceptor-ref name="exception"/>
    <interceptor-ref name="servletConfig"/>
    <interceptor-ref name="i18n"/>
    <interceptor-ref name="staticParams"/>
    <interceptor-ref name="actionMappingParams"/>
    <interceptor-ref name="params"/>
    <interceptor-ref name="alias"/>
    <interceptor-ref name="conversionError"/>
    <interceptor-ref name="validation"/>
    <interceptor-ref name="workflow"/>
</interceptor-stack>

There is no overwrite flag on this interceptor; the ordering above is the supported way to get that behavior.

Extending the Interceptor

This interceptor does not have any known extension points.

Examples

 <action name="someAction" class="com.examples.SomeAction">
     <!-- The value for the foo parameter will be applied as if it were named bar -->
     <param name="aliases">#{ 'foo' : 'bar' }</param>

     <interceptor-ref name="alias"/>
     <interceptor-ref name="basicStack"/>
     <result name="success">good_result.ftl</result>
 </action>
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