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55
56 package org.apache.commons.el;
57
58 import java.lang.reflect.Array JavaDoc;
59 import java.util.Collection JavaDoc;
60 import java.util.Map JavaDoc;
61 import javax.servlet.jsp.el.ELException JavaDoc;
62
63 /**
64  *
65  * <p>The implementation of the empty operator
66  *
67  * @author Nathan Abramson - Art Technology Group
68  * @version $Change: 181177 $$DateTime: 2001/06/26 08:45:09 $$Author: luehe $
69  **/
70
71 public class EmptyOperator
72   extends UnaryOperator
73 {
74   //-------------------------------------
75 // Singleton
76 //-------------------------------------
77
78   public static final EmptyOperator SINGLETON =
79     new EmptyOperator ();
80
81   //-------------------------------------
82 /**
83    *
84    * Constructor
85    **/
86   public EmptyOperator ()
87   {
88   }
89
90   //-------------------------------------
91 // Expression methods
92 //-------------------------------------
93 /**
94    *
95    * Returns the symbol representing the operator
96    **/
97   public String JavaDoc getOperatorSymbol ()
98   {
99     return "empty";
100   }
101
102   //-------------------------------------
103 /**
104    *
105    * Applies the operator to the given value
106    **/
107   public Object JavaDoc apply (Object JavaDoc pValue,
108                Logger pLogger)
109     throws ELException JavaDoc
110   {
111     // See if the value is null
112 if (pValue == null) {
113       return PrimitiveObjects.getBoolean (true);
114     }
115
116     // See if the value is a zero-length String
117 else if ("".equals (pValue)) {
118       return PrimitiveObjects.getBoolean (true);
119     }
120
121     // See if the value is a zero-length array
122 else if (pValue.getClass ().isArray () &&
123          Array.getLength (pValue) == 0) {
124       return PrimitiveObjects.getBoolean (true);
125     }
126
127     // See if the value is an empty Map
128 else if (pValue instanceof Map JavaDoc &&
129          ((Map JavaDoc) pValue).isEmpty ()) {
130       return PrimitiveObjects.getBoolean (true);
131     }
132
133     // See if the value is an empty Collection
134 else if (pValue instanceof Collection JavaDoc &&
135          ((Collection JavaDoc) pValue).isEmpty ()) {
136       return PrimitiveObjects.getBoolean (true);
137     }
138
139     // Otherwise, not empty
140 else {
141       return PrimitiveObjects.getBoolean (false);
142     }
143   }
144
145   //-------------------------------------
146 }
147
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