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Java > Open Source Codes > org > apache > commons > jelly > tags > core > WhenTag


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 }
60
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