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1   /*
2    * Copyright 2002,2004 The Apache Software Foundation.
3    *
4    * Licensed under the Apache License, Version 2.0 (the "License");
5    * you may not use this file except in compliance with the License.
6    * You may obtain a copy of the License at
7    *
8    *      http://www.apache.org/licenses/LICENSE-2.0
9    *
10   * Unless required by applicable law or agreed to in writing, software
11   * distributed under the License is distributed on an "AS IS" BASIS,
12   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13   * See the License for the specific language governing permissions and
14   * limitations under the License.
15   */
16  package org.apache.commons.jelly.tags.core;
17  
18  import org.apache.commons.jelly.JellyTagException;
19  import org.apache.commons.jelly.TagSupport;
20  import org.apache.commons.jelly.XMLOutput;
21  import org.apache.commons.jelly.expression.Expression;
22  
23  /*** A tag which conditionally evaluates its body based on some condition
24    *
25    * @author <a href="mailto:jstrachan@apache.org">James Strachan</a>
26    * @version $Revision: 155420 $
27    */
28  public class WhenTag extends TagSupport {
29  
30      /*** The expression to evaluate. */
31      private Expression test;
32  
33      public WhenTag() {
34      }
35  
36      // Tag interface
37      //-------------------------------------------------------------------------
38      public void doTag(XMLOutput output) throws JellyTagException {
39          ChooseTag tag = (ChooseTag) findAncestorWithClass( ChooseTag.class );
40          if ( tag == null ) {
41              throw new JellyTagException( "This tag must be enclosed inside a <choose> tag" );
42          }
43          if ( ! tag.isBlockEvaluated() && test != null ) {
44              if ( test.evaluateAsBoolean( context ) ) {
45                  tag.setBlockEvaluated(true);
46                  invokeBody(output);
47              }
48          }
49      }
50  
51      // Properties
52      //-------------------------------------------------------------------------
53  
54      /*** Sets the expression to evaluate. */
55      public void setTest(Expression test) {
56          this.test = test;
57      }
58  
59  }