1 /*
2 * $Header: /home/cvs/jakarta-commons/betwixt/src/java/org/apache/commons/betwixt/expression/IteratorExpression.java,v 1.2 2002/07/01 18:55:39 rdonkin Exp $
3 * $Revision: 1.2 $
4 * $Date: 2002/07/01 18:55:39 $
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,
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47 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
48 * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
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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
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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 1.2 2002/07/01 18:55:39 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.ArrayIterator;
72 import org.apache.commons.collections.EnumerationIterator;
73 import org.apache.commons.collections.SingletonIterator;
74
75 /*** <p><code>IteratorExpression</code> returns an iterator over the current context.</p>
76 *
77 * @author <a href="mailto:jstrachan@apache.org">James Strachan</a>
78 * @version $Revision: 1.2 $
79 */
80 public class IteratorExpression implements Expression {
81
82 /*** Use this <code>Expression</code> to perform initial evaluation*/
83 private Expression expression;
84
85 /*** Construct <code>IteratorExpression</code> using given expression for initial evaluation.
86 */
87 public IteratorExpression(Expression expression) {
88 this.expression = expression;
89 }
90
91 /*** Returns an interator over the current context */
92 public Object evaluate(Context context) {
93 // evaluate wrapped expression against context
94 Object value = expression.evaluate( context );
95
96 // based on the class of the result,
97 // return an appropriate iterator
98 if ( value instanceof Iterator ) {
99 // if the value is an iterator, we're done
100 return (Iterator) value;
101 }
102 else if ( value instanceof Collection ) {
103 // if it's a collection, return an iterator for that collection
104 Collection collection = (Collection) value;
105 return collection.iterator();
106 }
107 else if ( value instanceof Map ) {
108 // if it's a map, return an iterator for the map entries
109 Map map = (Map) value;
110 return map.entrySet().iterator();
111 }
112 else if ( value instanceof Enumeration ) {
113 // if it's an enumeration, wrap it in an EnumerationIterator
114 return new EnumerationIterator( (Enumeration) value );
115 }
116 else if ( value != null ) {
117 // if we have an array return an ArrayIterator
118 Class type = value.getClass();
119 if ( type.isArray() ) {
120 return new ArrayIterator( value );
121 }
122 }
123
124 // we've got something we can't deal with
125 // so return an empty iterator
126 return Collections.EMPTY_LIST.iterator();
127 }
128
129 public void update(Context context, String newValue) {
130 // do nothing
131 }
132
133 public String toString() {
134 return "IteratorExpression [expression=" + expression + "]";
135 }
136 }
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