1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one or more
3 * contributor license agreements. See the NOTICE file distributed with
4 * this work for additional information regarding copyright ownership.
5 * The ASF licenses this file to You under the Apache License, Version 2.0
6 * (the "License"); you may not use this file except in compliance with
7 * the License. You may obtain a copy of the License at
8 *
9 * http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 */
17 package org.apache.commons.el;
18
19 import java.lang.reflect.Array;
20 import java.util.Collection;
21 import java.util.Map;
22
23 import javax.servlet.jsp.el.ELException;
24
25 /**
26 *
27 * <p>The implementation of the empty operator
28 *
29 * @author Nathan Abramson - Art Technology Group
30 * @version $Change: 181177 $$DateTime: 2001/06/26 08:45:09 $$Author: bayard $
31 **/
32
33 public class EmptyOperator
34 extends UnaryOperator
35 {
36 //-------------------------------------
37 // Singleton
38 //-------------------------------------
39
40 public static final EmptyOperator SINGLETON =
41 new EmptyOperator ();
42
43 //-------------------------------------
44 /**
45 *
46 * Constructor
47 **/
48 public EmptyOperator ()
49 {
50 }
51
52 //-------------------------------------
53 // Expression methods
54 //-------------------------------------
55 /**
56 *
57 * Returns the symbol representing the operator
58 **/
59 public String getOperatorSymbol ()
60 {
61 return "empty";
62 }
63
64 //-------------------------------------
65 /**
66 *
67 * Applies the operator to the given value
68 **/
69 public Object apply (Object pValue)
70 throws ELException
71 {
72 // See if the value is null
73 if (pValue == null) {
74 return PrimitiveObjects.getBoolean (true);
75 }
76
77 // See if the value is a zero-length String
78 else if ("".equals (pValue)) {
79 return PrimitiveObjects.getBoolean (true);
80 }
81
82 // See if the value is a zero-length array
83 else if (pValue.getClass ().isArray () &&
84 Array.getLength (pValue) == 0) {
85 return PrimitiveObjects.getBoolean (true);
86 }
87
88 // See if the value is an empty Map
89 else if (pValue instanceof Map &&
90 ((Map) pValue).isEmpty ()) {
91 return PrimitiveObjects.getBoolean (true);
92 }
93
94 // See if the value is an empty Collection
95 else if (pValue instanceof Collection &&
96 ((Collection) pValue).isEmpty ()) {
97 return PrimitiveObjects.getBoolean (true);
98 }
99
100 // Otherwise, not empty
101 else {
102 return PrimitiveObjects.getBoolean (false);
103 }
104 }
105
106 //-------------------------------------
107 }