org.apache.struts2.components

Class Param

java.lang.Object

org.apache.struts2.components.Component

org.apache.struts2.components.Param

public class Param
extends Component

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 addParamter method. For unnamed parameters the Tag must implement the Param.UnnamedParametric interface defined in this class (e.g. The TextTag does this).

This tag has the following two paramters.

• 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.

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.

This second example demonstrates how the text tag can use parameters from this param tag.

 <s:text name="cart.total.cost">
     <s:param value="#session.cartTotal"/>
 </s:text>
 

See Also:

Include, Bean, Text

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static interface	Param.UnnamedParametric Tags can implement this to support nested param tags without the name attribute.

Field Summary

Fields

Modifier and Type	Field and Description
protected String	name
protected boolean	suppressEmptyParameters
protected String	value

Fields inherited from class org.apache.struts2.components.Component

actionMapper, COMPONENT_STACK, devMode, parameters, stack, standardAttributesMap, throwExceptionOnELFailure

Constructor Summary

Constructors

Constructor and Description
Param(ValueStack stack)

Method Summary

Modifier and Type	Method and Description
boolean	end(Writer writer, String body) Callback for the end tag of this component.
void	setName(String name)
void	setSuppressEmptyParameters(boolean suppressEmptyParameters)
void	setValue(String value)
boolean	usesBody() Overwrite to set if body should be used.

Methods inherited from class org.apache.struts2.components.Component

addAllParameters, addParameter, altSyntax, completeExpressionIfAltSyntax, copyParams, determineActionURL, determineNamespace, end, escapeHtmlBody, fieldError, findAncestor, findString, findString, findStringIfAltSyntax, findValue, findValue, findValue, getComponentStack, getParameters, getStack, getStandardAttributes, isValidTagAttribute, popComponentStack, setActionMapper, setDevMode, setThrowExceptionsOnELFailure, setUrlHelper, start, stripExpressionIfAltSyntax, toString

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

name

protected String name

value

protected String value

suppressEmptyParameters

protected boolean suppressEmptyParameters

Constructor Detail

Param

public Param(ValueStack stack)

Method Detail

end

public boolean end(Writer writer,
                   String body)

Description copied from class: Component

Callback for the end tag of this component. Should the body be evaluated again?
NOTE: will pop component stack.

Overrides:

end in class Component

Parameters:

writer - the output writer.

body - the rendered body.

Returns:

true if the body should be evaluated again

usesBody

public boolean usesBody()

Description copied from class: Component

Overwrite to set if body should be used.

Overrides:

usesBody in class Component

Returns:

always false for this component.

setName

public void setName(String name)

setValue

public void setValue(String value)

setSuppressEmptyParameters

public void setSuppressEmptyParameters(boolean suppressEmptyParameters)