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1   /*
2    * $Id: Param.java 497654 2007-01-19 00:21:57Z rgielen $
3    *
4    * Licensed to the Apache Software Foundation (ASF) under one
5    * or more contributor license agreements.  See the NOTICE file
6    * distributed with this work for additional information
7    * regarding copyright ownership.  The ASF licenses this file
8    * to you under the Apache License, Version 2.0 (the
9    * "License"); you may not use this file except in compliance
10   * with the License.  You may obtain a copy of the License at
11   *
12   *  http://www.apache.org/licenses/LICENSE-2.0
13   *
14   * Unless required by applicable law or agreed to in writing,
15   * software distributed under the License is distributed on an
16   * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
17   * KIND, either express or implied.  See the License for the
18   * specific language governing permissions and limitations
19   * under the License.
20   */
21  package org.apache.struts2.components;
22  
23  import java.io.Writer;
24  
25  import org.apache.struts2.views.annotations.StrutsTag;
26  import org.apache.struts2.views.annotations.StrutsTagAttribute;
27  import org.apache.struts2.StrutsException;
28  
29  import com.opensymphony.xwork2.util.ValueStack;
30  
31  /***
32   * <!-- START SNIPPET: javadoc -->
33   * <p>This tag can be used to parameterize other tags.</p>
34   * The include tag and bean tag are examples of such tags.
35   * <p/>
36   * The parameters can be added with or without a name as key.
37   * If the tag provides a name attribute the parameters are added using the
38   * {@link Component#addParameter(String, Object) addParamter} method.
39   * For unnamed parameters the Tag must implement the {@link UnnamedParametric} interface defined in
40   * this class (e.g. The TextTag does this).
41   * <p/>
42   * This tag has the following two paramters.
43   * <!-- START SNIPPET: params -->
44   * <ul>
45   *      <li>name (String) - the name of the parameter</li>
46   *      <li>value (Object) - the value of the parameter</li>
47   * </ul>
48   * <!-- END SNIPPET: params -->
49   * <p/>
50   * <b>Note:</b>
51   * When you declare the param tag, the value can be defined in either a <tt>value</tt> attribute or
52   * as text between the start and end tag. Struts behaves a bit different according to these two situations.
53   * This is best illustrated using an example:
54   * <br/>&lt;param name="color"&gt;blue&lt;/param&gt; &lt;-- (A) --&gt;
55   * <br/>&lt;param name="color" value="blue"/&gt; &lt;-- (B) --&gt;
56   * <br/>In the first situation (A) the value would be evaluated to the stack as a <tt>java.lang.String</tt> object.
57   * And in situation (B) the value would be evaluated to the stack as a <tt>java.lang.Object</tt> object.
58   * <br/>For more information see <a href="http://jira.opensymphony.com/browse/WW-808">WW-808</a>.
59   * <!-- END SNIPPET: javadoc -->
60   *
61   * <p/> <b>Examples</b>
62   * <!-- START SNIPPET: example -->
63   * <pre>
64   * &lt;ui:component&gt;
65   *  &lt;ui:param name="key"     value="[0]"/&gt;
66   *  &lt;ui:param name="value"   value="[1]"/&gt;
67   *  &lt;ui:param name="context" value="[2]"/&gt;
68   * &lt;/ui:component&gt;
69   * </pre>
70   * <!-- END SNIPPET: example -->
71   * <p/>
72   * <!-- START SNIPPET: exampledescription -->
73   * where the key will be the identifier and the value the result of an OGNL expression run against the current
74   * ValueStack.
75   * <!-- END SNIPPET: exampledescription -->
76   * <p/>
77   * This second example demonstrates how the text tag can use parameters from this param tag.
78   * <!-- START SNIPPET: example2 -->
79   * <pre>
80   * &lt;s:text name="cart.total.cost"&gt;
81   *     &lt;s:param value="#session.cartTotal"/&gt;
82   * &lt;/s:text&gt;
83   * </pre>
84   * <!-- END SNIPPET: example2 -->
85   * <p/>
86   *
87   * @see Include
88   * @see Bean
89   * @see Text
90   *
91   */
92  @StrutsTag(name="param", tldTagClass="org.apache.struts2.views.jsp.ParamTag", description="Parametrize other tags")
93  public class Param extends Component {
94      protected String name;
95      protected String value;
96  
97      public Param(ValueStack stack) {
98          super(stack);
99      }
100 
101     public boolean end(Writer writer, String body) {
102         Component component = findAncestor(Component.class);
103         if (value != null) {
104             if (component instanceof UnnamedParametric) {
105                 ((UnnamedParametric) component).addParameter(findValue(value));
106             } else {
107                 String name = findString(this.name);
108 
109                 if (name == null) {
110                     throw new StrutsException("No name found for following expression: " + name);
111                 }
112 
113                 Object value = findValue(this.value);
114                 component.addParameter(name, value);
115             }
116         } else {
117             if (component instanceof UnnamedParametric) {
118                 ((UnnamedParametric) component).addParameter(body);
119             } else {
120                 component.addParameter(findString(name), body);
121             }
122         }
123 
124         return super.end(writer, "");
125     }
126 
127     public boolean usesBody() {
128         return true;
129     }
130 
131     @StrutsTagAttribute(description="Name of Parameter to set")
132     public void setName(String name) {
133         this.name = name;
134     }
135 
136     @StrutsTagAttribute(description="Value expression for Parameter to set", defaultValue="The value of evaluating provided name against stack")
137     public void setValue(String value) {
138         this.value = value;
139     }
140 
141 
142     /***
143      * Tags can implement this to support nested param tags without the <tt>name</tt> attribute.
144      * <p/>
145      * The {@link Text TextTag} uses this approach. For unnamed parameters an example is given in the class
146      * javadoc for {@link Param ParamTag}.
147      */
148     public interface UnnamedParametric {
149 
150         /***
151          * Adds the given value as a parameter to the outer tag.
152          * @param value  the value
153          */
154         public void addParameter(Object value);
155     }
156 
157 }