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layout: default title: param tag parent: title: Tag Reference url: tag-reference.html

param

Please make sure you have read the Tag Syntax document and understand how tag attribute syntax works.

Description

This tag can be used to parameterize other tags. The include tag and bean tag are examples of such tags.

The parameters can be added with or without a name as key. If the tag provides a name attribute the parameters are added using the Component#addParameter(String, Object) method. For unnamed parameters the tag must implement the UnnamedParametric interface defined in this class (e.g. The TextTag does this).

This tag has the following two parameters.

• name (String) - the name of the parameter
• value (Object) - the value of the parameter
• suppressEmptyParameters (boolean) - whether to suppress this parameter if empty

NOTE: When you declare the param tag, the value can be defined in either a value attribute or as text between the start and end tag. Struts behaves a bit different according to these two situations. This is best illustrated using an example: <param name="color">blue</param> (A) <param name="color" value="blue"/> (B) In the first situation (A) the value would be evaluated to the stack as a java.lang.String object. And in situation (B) the value would be evaluated to the stack as a java.lang.Object object. For more information see WW-808.

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Attributes

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Examples

<ui:component>
 <ui:param name="key"     value="[0]"/>
 <ui:param name="value"   value="[1]"/>
 <ui:param name="context" value="[2]"/>
</ui:component>

Whether to suppress empty parameters:

<s:url action="eventAdd">
  <s:param name="bean.searchString" value="%{bean.searchString}" />
  <s:param name="bean.filter" value="%{bean.filter}" />
  <s:param name="bean.pageNum" value="%{pager.pageNumber}" suppressEmptyParameters="true" />
</s:url>

where the key will be the identifier and the value the result of an OGNL expression run against the current ValueStack.