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Param.javaAPI DocExample5857Mon Jul 23 13:26:36 BST 2007org.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 {@link Component#addParameter(String, Object) addParamter} method. For unnamed parameters the Tag must implement the {@link 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

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>

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
Include
see
Bean
see
Text

Fields Summary
protected String
name
protected String
value
Constructors Summary
public Param(com.opensymphony.xwork2.util.ValueStack stack)

        super(stack);
Methods Summary
public booleanend(java.io.Writer writer, java.lang.String body)

        Component component = findAncestor(Component.class);
        if (value != null) {
            if (component instanceof UnnamedParametric) {
                ((UnnamedParametric) component).addParameter(findValue(value));
            } else {
                String name = findString(this.name);

                if (name == null) {
                    throw new StrutsException("No name found for following expression: " + name);
                }

                Object value = findValue(this.value);
                component.addParameter(name, value);
            }
        } else {
            if (component instanceof UnnamedParametric) {
                ((UnnamedParametric) component).addParameter(body);
            } else {
                component.addParameter(findString(name), body);
            }
        }

        return super.end(writer, "");
public voidsetName(java.lang.String name)

        this.name = name;
public voidsetValue(java.lang.String value)

        this.value = value;
public booleanusesBody()

        return true;