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1   /*
2    * $Id: EmptyTag.java 471754 2006-11-06 14:55:09Z husted $
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.struts.taglib.logic;
22  
23  import org.apache.struts.taglib.TagUtils;
24  
25  import javax.servlet.jsp.JspException;
26  
27  import java.lang.reflect.Array;
28  
29  import java.util.Collection;
30  import java.util.Map;
31  
32  /**
33   * Evalute the nested body content of this tag if the specified value is empty
34   * for this request.
35   *
36   * @version $Rev: 471754 $ $Date: 2004-10-16 12:38:42 -0400 (Sat, 16 Oct 2004)
37   *          $
38   * @since Struts 1.1
39   */
40  public class EmptyTag extends ConditionalTagBase {
41      // ------------------------------------------------------ Protected Methods
42  
43      /**
44       * Evaluate the condition that is being tested by this particular tag, and
45       * return <code>true</code> if the nested body content of this tag should
46       * be evaluated, or <code>false</code> if it should be skipped. This
47       * method must be implemented by concrete subclasses.
48       *
49       * @throws JspException if a JSP exception occurs
50       */
51      protected boolean condition()
52          throws JspException {
53          return (condition(true));
54      }
55  
56      /**
57       * Evaluate the condition that is being tested by this particular tag, and
58       * return <code>true</code> if the nested body content of this tag should
59       * be evaluated, or <code>false</code> if it should be skipped. This
60       * method must be implemented by concrete subclasses.
61       *
62       * @param desired Desired outcome for a true result
63       * @throws JspException if a JSP exception occurs
64       */
65      protected boolean condition(boolean desired)
66          throws JspException {
67          if (this.name == null) {
68              JspException e =
69                  new JspException(messages.getMessage("empty.noNameAttribute"));
70  
71              TagUtils.getInstance().saveException(pageContext, e);
72              throw e;
73          }
74  
75          Object value = null;
76  
77          if (this.property == null) {
78              value = TagUtils.getInstance().lookup(pageContext, name, scope);
79          } else {
80              value =
81                  TagUtils.getInstance().lookup(pageContext, name, property, scope);
82          }
83  
84          boolean empty = true;
85  
86          if (value == null) {
87              empty = true;
88          } else if (value instanceof String) {
89              String strValue = (String) value;
90  
91              empty = (strValue.length() < 1);
92          } else if (value instanceof Collection) {
93              Collection collValue = (Collection) value;
94  
95              empty = collValue.isEmpty();
96          } else if (value instanceof Map) {
97              Map mapValue = (Map) value;
98  
99              empty = mapValue.isEmpty();
100         } else if (value.getClass().isArray()) {
101             empty = Array.getLength(value) == 0;
102         } else {
103             empty = false;
104         }
105 
106         return (empty == desired);
107     }
108 }