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# Parameter Selector

- Name : ParameterSelector
- Class: org.apache.cocoon.selection.ParameterSelector
- Cacheable: not applicable

This Selector matches a string, in the Parameters object passed to the selector, against a specified Cocoon internal parameter. It performs a case-sensitive string comparison between the value of the 'parameter-selector-test' parameter and the value of the 'test' attribute of the `<map:when ...>` element.

This internal parameter could be:

- A sitemap parameter from the `<map:match ...>` portion of the pipeline
- A sitemap parameter set by an action

## Reasons to use ParameterSelector

One purpose of this selector is to choose between different components of a pipeline based on sitemap parameters set by an action. This would allow the action to control the logic required to set one or more parameters, which can then be used by this selector to control pipeline processing. Thus, complex decision-making logic can be contained in actions, while the sitemap simply uses the results of the actions (the parameters) to determine pipeline processing.

Parameter Selector can also be used to select on the value of 'keys' (such as {1} or {../2} ) from the wildcard matcher. Information in the URI, such as part of a filename, can then be used to determine pipeline processing.

## Examples

Add the component to your sitemap.xmap:

       <map:components>
        ...
        <map:selectors>
         ...
         <map:selector
          name="parameter"
            logger="sitemap.selector.parameter"
            src="org.apache.cocoon.selection.ParameterSelector"/>
         ...

Use a parameter set by an action:

Assume there is an action (named MyAction) that sets a parameter (named MyRegion) to several possible values. For more information on actions, including a simple example of an action that creates a sitemap parameter, see Creating and Using Actions.

       <map:match pattern="*.xml">
        <map:act type="MyAction">
          <map:generate src="{../1}.xml"/>

          <map:select type="parameter">
            <map:parameter name="parameter-selector-test" value="{MyRegion}"/>

            <!-- executes iff the value of MyRegion equals
                 "United States" (without quotes) -->
            <map:when test="United States">
              <map:transform src="stylesheets/us.xsl"/>
            </map:when>

            <map:when test="South_America">
              <map:transform src="stylesheets/southamerica.xsl"/>
            </map:when>

            <map:when test="Europe">
              <map:transform src="stylesheets/europe.xsl"/>
            </map:when>

            <map:otherwise>
              <map:transform src="all_others.xsl"
            </map:otherwise>

          </map:select>
        </map:act>
        <map:serialize/>
      </map:match>

Use values from the URI:

       <map:pipeline>
         <!-- {1}/{2}/myfile.xml -->
         <map:match pattern="**/*/myfile.xml">

           <!-- Use ParameterSelector -->
           <map:select type="parameter">
            <map:parameter name="parameter-selector-test" value="{2}"/>

            <!-- executes iff the value of {2} equals
                 "basic" (without quotes); the requested URI
                  could be **/basic/myfile.xml -->
            <map:when test="basic">
                <map:generate src="{1}/myfile.xml"/>
                <map:transform src="stylesheets/basic.xsl">
                    <map:parameter name="use-request-parameters" value="true"/>
                    <map:parameter name="resource" value="{2}.html"/>
                </map:transform>
                <map:serialize/>
            </map:when>

            <map:when test="aggregate">
                <map:aggregate element="site">
              <map:part src="cocoon:/{1}/sidebar-{1}/{2}.xml"/>
              <map:part src="cocoon:/body-{1}/{2}.xsp"/>
                </map:aggregate>
                <map:transform src="stylesheets/aggregate2xhtml.xsl"/>
                <map:serialize/>
            </map:when>

            <map:otherwise>
                <map:redirect-to uri="other_URI"/>
            </map:otherwise>

          </map:select>
        </map:match>
        ...

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