1 /*
2 * $Header: /home/cvs/jakarta-commons/betwixt/src/java/org/apache/commons/betwixt/expression/IteratorExpression.java,v 1.5 2003/01/09 22:34:07 rdonkin Exp $
3 * $Revision: 1.5 $
4 * $Date: 2003/01/09 22:34:07 $
5 *
6 * ====================================================================
7 *
8 * The Apache Software License, Version 1.1
9 *
10 * Copyright (c) 1999-2002 The Apache Software Foundation. All rights
11 * reserved.
12 *
13 * Redistribution and use in source and binary forms, with or without
14 * modification, are permitted provided that the following conditions
15 * are met:
16 *
17 * 1. Redistributions of source code must retain the above copyright
18 * notice, this list of conditions and the following disclaimer.
19 *
20 * 2. Redistributions in binary form must reproduce the above copyright
21 * notice, this list of conditions and the following disclaimer in
22 * the documentation and/or other materials provided with the
23 * distribution.
24 *
25 * 3. The end-user documentation included with the redistribution, if
26 * any, must include the following acknowlegement:
27 * "This product includes software developed by the
28 * Apache Software Foundation (http://www.apache.org/)."
29 * Alternately, this acknowlegement may appear in the software itself,
30 * if and wherever such third-party acknowlegements normally appear.
31 *
32 * 4. The names "The Jakarta Project", "Commons", and "Apache Software
33 * Foundation" must not be used to endorse or promote products derived
34 * from this software without prior written permission. For written
35 * permission, please contact apache@apache.org.
36 *
37 * 5. Products derived from this software may not be called "Apache"
38 * nor may "Apache" appear in their names without prior written
39 * permission of the Apache Group.
40 *
41 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
42 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
43 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
44 * DISCLAIMED. IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
45 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
46 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
47 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
48 * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
49 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
50 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
51 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
52 * SUCH DAMAGE.
53 * ====================================================================
54 *
55 * This software consists of voluntary contributions made by many
56 * individuals on behalf of the Apache Software Foundation. For more
57 * information on the Apache Software Foundation, please see
58 * <http://www.apache.org/>.
59 *
60 * $Id: IteratorExpression.java,v 1.5 2003/01/09 22:34:07 rdonkin Exp $
61 */
62
63 package org.apache.commons.betwixt.expression;
64
65 import java.util.Collection;
66 import java.util.Collections;
67 import java.util.Enumeration;
68 import java.util.Iterator;
69 import java.util.Map;
70
71 import org.apache.commons.collections.iterators.ArrayIterator;
72 import org.apache.commons.collections.iterators.EnumerationIterator;
73
74 /*** <p><code>IteratorExpression</code> returns an iterator over the current context.</p>
75 *
76 * @author <a href="mailto:jstrachan@apache.org">James Strachan</a>
77 * @version $Revision: 1.5 $
78 */
79 public class IteratorExpression implements Expression {
80
81 /*** Use this <code>Expression</code> to perform initial evaluation*/
82 private Expression expression;
83
84 /***
85 * Construct <code>IteratorExpression</code> using given expression for initial evaluation.
86 * @param expression this expression will be evaluated and the result converted to an
87 * iterator.
88 */
89 public IteratorExpression(Expression expression) {
90 this.expression = expression;
91 }
92
93 /***
94 * Returns an interator over the current context
95 * @see org.apache.commons.betwixt.expression.Expression
96 */
97 public Object evaluate(Context context) {
98 // evaluate wrapped expression against context
99 Object value = expression.evaluate( context );
100
101 // based on the class of the result,
102 // return an appropriate iterator
103 if ( value instanceof Iterator ) {
104 // if the value is an iterator, we're done
105 return (Iterator) value;
106
107 } else if ( value instanceof Collection ) {
108 // if it's a collection, return an iterator for that collection
109 Collection collection = (Collection) value;
110 return collection.iterator();
111
112 } else if ( value instanceof Map ) {
113 // if it's a map, return an iterator for the map entries
114 Map map = (Map) value;
115 return map.entrySet().iterator();
116
117 } else if ( value instanceof Enumeration ) {
118 // if it's an enumeration, wrap it in an EnumerationIterator
119 return new EnumerationIterator( (Enumeration) value );
120
121 } else if ( value != null ) {
122 // if we have an array return an ArrayIterator
123 Class type = value.getClass();
124 if ( type.isArray() ) {
125 return new ArrayIterator( value );
126 }
127 }
128
129 // we've got something we can't deal with
130 // so return an empty iterator
131 return Collections.EMPTY_LIST.iterator();
132 }
133
134 /***
135 * Do nothing
136 * @see org.apache.commons.betwixt.expression.Expression
137 */
138 public void update(Context context, String newValue) {
139 // do nothing
140 }
141
142 /***
143 * Returns something useful for logging
144 * @return string useful for logging
145 */
146 public String toString() {
147 return "IteratorExpression [expression=" + expression + "]";
148 }
149 }
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