EmptyOperator


1   /*
2    * Copyright 1999-2004 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  
18  
19  package org.apache.taglibs.standard.lang.jstl;
20  
21  
22  
23  import java.lang.reflect.Array  ;
24  
25  import java.util.Collection  ;
26  
27  import java.util.Map  ;
28  
29  
30  
31  /**
32  
33   *
34  
35   * <p>The implementation of the empty operator
36  
37   * 
38  
39   * @author Nathan Abramson - Art Technology Group
40  
41   * @version $Change: 181177 $$DateTime: 2001/06/26 08:45:09 $$Author: pierred $
42  
43   **/
44  
45  
46  
47  public class EmptyOperator
48  
49    extends UnaryOperator
50  
51  {
52  
53    //-------------------------------------
54  
55    // Singleton
56  
57    //-------------------------------------
58  
59  
60  
61    public static final EmptyOperator SINGLETON =
62  
63      new EmptyOperator ();
64  
65  
66  
67    //-------------------------------------
68  
69    /**
70  
71     *
72  
73     * Constructor
74  
75     **/
76  
77    public EmptyOperator ()
78  
79    {
80  
81    }
82  
83  
84  
85    //-------------------------------------
86  
87    // Expression methods
88  
89    //-------------------------------------
90  
91    /**
92  
93     *
94  
95     * Returns the symbol representing the operator
96  
97     **/
98  
99    public String   getOperatorSymbol ()
100 
101   {
102 
103     return "empty";
104 
105   }
106 
107 
108 
109   //-------------------------------------
110 
111   /**
112 
113    *
114 
115    * Applies the operator to the given value
116 
117    **/
118 
119   public Object   apply (Object   pValue,
120 
121                Object   pContext,
122 
123                Logger pLogger)
124 
125     throws ELException
126 
127   {
128 
129     // See if the value is null
130 
131     if (pValue == null) {
132 
133       return PrimitiveObjects.getBoolean (true);
134 
135     }
136 
137 
138 
139     // See if the value is a zero-length String
140 
141     else if ("".equals (pValue)) {
142 
143       return PrimitiveObjects.getBoolean (true);
144 
145     }
146 
147 
148 
149     // See if the value is a zero-length array
150 
151     else if (pValue.getClass ().isArray () &&
152 
153          Array.getLength (pValue) == 0) {
154 
155       return PrimitiveObjects.getBoolean (true);
156 
157     }
158 
159 
160 
161     // See if the value is an empty Collection
162 
163     else if (pValue instanceof Collection   &&
164 
165          ((Collection  ) pValue).isEmpty ()) {
166 
167       return PrimitiveObjects.getBoolean (true);
168 
169     }
170 
171 
172 
173     // See if the value is an empty Map
174 
175     else if (pValue instanceof Map   &&
176 
177          ((Map  ) pValue).isEmpty ()) {
178 
179       return PrimitiveObjects.getBoolean (true);
180 
181     }
182 
183 
184 
185     // Otherwise, not empty
186 
187     else {
188 
189       return PrimitiveObjects.getBoolean (false);
190 
191     }
192 
193   }
194 
195 
196 
197   //-------------------------------------
198 
199 }
200 
201
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