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


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
17 package org.apache.commons.jelly.tags.core;
18
19 import org.apache.commons.jelly.JellyTagException;
20 import org.apache.commons.jelly.MissingAttributeException;
21 import org.apache.commons.jelly.TagSupport;
22 import org.apache.commons.jelly.XMLOutput;
23 import org.apache.commons.jelly.expression.Expression;
24 import org.apache.commons.jelly.impl.BreakException;
25 import org.apache.commons.logging.Log;
26 import org.apache.commons.logging.LogFactory;
27
28 /**
29  * A tag which performs an iteration while the result of an expression is true.
30  *
31  * @author <a HREF="mailto:eric@ericalexander.net">Eric Alexander</a>
32  * @author dIon Gillard
33  * @version $Revision: 155420 $
34  */
35 public class WhileTag extends TagSupport {
36
37     /** The Log to which logging calls will be made. */
38     private static final Log log = LogFactory.getLog(WhileTag.class);
39
40     /** The expression to use to determine if the while should continue */
41     private Expression test;
42
43     /**
44      * Create a new while tag
45      */
46     public WhileTag() {
47     }
48
49     /**
50      * Tag interface
51      * @param output destination for xml output
52      * @throws MissingAttributeException when the test attribute is missing
53      * @throws Exception for anything else
54      */
55     public void doTag(XMLOutput output) throws MissingAttributeException, JellyTagException {
56         if (test != null) {
57             try {
58                 while (test.evaluateAsBoolean(getContext())) {
59                     if (log.isDebugEnabled()) {
60                         log.debug("evaluated to true! gonna keep on chuggin!");
61                     }
62                     invokeBody(output);
63                 }
64             }
65             catch (BreakException e) {
66                 if (log.isDebugEnabled()) {
67                     log.debug("loop terminated by break: " + e, e);
68                 }
69             }
70         }
71         else {
72             throw new MissingAttributeException("test");
73         }
74     }
75
76     // Properties
77 //-------------------------------------------------------------------------
78
79     /**
80      * Setter for the expression
81      * @param e the expression to test
82      */
83     public void setTest(Expression e) {
84         this.test = e;
85     }
86 }
87
88
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