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18 package org.apache.commons.beanutils;
19
20 import org.apache.commons.collections.Transformer;
21 import org.apache.commons.logging.Log;
22 import org.apache.commons.logging.LogFactory;
23
24 import java.lang.reflect.InvocationTargetException;
25
26
27 /***
28 * <p><code>Transformer</code> that outputs a property value.</p>
29 *
30 * <p>An implementation of <code>org.apache.commons.collections.Transformer</code> that transforms
31 * the object provided by returning the value of a specified property of the object. The
32 * constructor for <code>BeanToPropertyValueTransformer</code> requires the name of the property
33 * that will be used in the transformation. The property can be a simple, nested, indexed, or
34 * mapped property as defined by <code>org.apache.commons.beanutils.PropertyUtils</code>. If any
35 * object in the property path specified by <code>propertyName</code> is <code>null</code> then the
36 * outcome is based on the value of the <code>ignoreNull</code> attribute.
37 * </p>
38 *
39 * <p>
40 * A typical usage might look like:
41 * <code><pre>
42 * // create the transformer
43 * BeanToPropertyValueTransformer transformer = new BeanToPropertyValueTransformer( "person.address.city" );
44 *
45 * // transform the Collection
46 * Collection peoplesCities = CollectionUtils.collect( peopleCollection, transformer );
47 * </pre></code>
48 * </p>
49 *
50 * <p>
51 * This would take a <code>Collection</code> of person objects and return a <code>Collection</code>
52 * of objects which represents the cities in which each person lived. Assuming...
53 * <ul>
54 * <li>
55 * The top level object in the <code>peeopleCollection</code> is an object which represents a
56 * person.
57 * </li>
58 * <li>
59 * The person object has a <code>getAddress()</code> method which returns an object which
60 * represents a person's address.
61 * </li>
62 * <li>
63 * The address object has a <code>getCity()</code> method which returns an object which
64 * represents the city in which a person lives.
65 * </li>
66 * </ul>
67 *
68 * @author Norm Deane
69 * @see org.apache.commons.beanutils.PropertyUtils
70 * @see org.apache.commons.collections.Transformer
71 */
72 public class BeanToPropertyValueTransformer implements Transformer {
73
74 /*** For logging. */
75 private final Log log = LogFactory.getLog(this.getClass());
76
77 /*** The name of the property that will be used in the transformation of the object. */
78 private String propertyName;
79
80 /***
81 * <p>Should null objects on the property path throw an <code>IllegalArgumentException</code>?</p>
82 * <p>
83 * Determines whether <code>null</code> objects in the property path will genenerate an
84 * <code>IllegalArgumentException</code> or not. If set to <code>true</code> then if any objects
85 * in the property path evaluate to <code>null</code> then the
86 * <code>IllegalArgumentException</code> throw by <code>PropertyUtils</code> will be logged but
87 * not rethrown and <code>null</code> will be returned. If set to <code>false</code> then if any
88 * objects in the property path evaluate to <code>null</code> then the
89 * <code>IllegalArgumentException</code> throw by <code>PropertyUtils</code> will be logged and
90 * rethrown.
91 * </p>
92 */
93 private boolean ignoreNull;
94
95 /***
96 * Constructs a Transformer which does not ignore nulls.
97 * Constructor which takes the name of the property that will be used in the transformation and
98 * assumes <code>ignoreNull</code> to be <code>false</code>.
99 *
100 * @param propertyName The name of the property that will be used in the transformation.
101 * @throws IllegalArgumentException If the <code>propertyName</code> is <code>null</code> or
102 * empty.
103 */
104 public BeanToPropertyValueTransformer(String propertyName) {
105 this(propertyName, false);
106 }
107
108 /***
109 * Constructs a Transformer and sets ignoreNull.
110 * Constructor which takes the name of the property that will be used in the transformation and
111 * a boolean which determines whether <code>null</code> objects in the property path will
112 * genenerate an <code>IllegalArgumentException</code> or not.
113 *
114 * @param propertyName The name of the property that will be used in the transformation.
115 * @param ignoreNull Determines whether <code>null</code> objects in the property path will
116 * genenerate an <code>IllegalArgumentException</code> or not.
117 * @throws IllegalArgumentException If the <code>propertyName</code> is <code>null</code> or
118 * empty.
119 */
120 public BeanToPropertyValueTransformer(String propertyName, boolean ignoreNull) {
121 super();
122
123 if ((propertyName != null) && (propertyName.length() > 0)) {
124 this.propertyName = propertyName;
125 this.ignoreNull = ignoreNull;
126 } else {
127 throw new IllegalArgumentException(
128 "propertyName cannot be null or empty");
129 }
130 }
131
132 /***
133 * Returns the value of the property named in the transformer's constructor for
134 * the object provided. If any object in the property path leading up to the target property is
135 * <code>null</code> then the outcome will be based on the value of the <code>ignoreNull</code>
136 * attribute. By default, <code>ignoreNull</code> is <code>false</code> and would result in an
137 * <code>IllegalArgumentException</code> if an object in the property path leading up to the
138 * target property is <code>null</code>.
139 *
140 * @param object The object to be transformed.
141 * @return The value of the property named in the transformer's constructor for the object
142 * provided.
143 * @throws IllegalArgumentException If an IllegalAccessException, InvocationTargetException, or
144 * NoSuchMethodException is thrown when trying to access the property specified on the object
145 * provided. Or if an object in the property path provided is <code>null</code> and
146 * <code>ignoreNull</code> is set to <code>false</code>.
147 */
148 public Object transform(Object object) {
149
150 Object propertyValue = null;
151
152 try {
153 propertyValue = PropertyUtils.getProperty(object, propertyName);
154 } catch (IllegalArgumentException e) {
155 final String errorMsg = "Problem during transformation. Null value encountered in property path...";
156
157 if (ignoreNull) {
158 log.warn("WARNING: " + errorMsg, e);
159 } else {
160 log.error("ERROR: " + errorMsg, e);
161 throw e;
162 }
163 } catch (IllegalAccessException e) {
164 final String errorMsg = "Unable to access the property provided.";
165 log.error(errorMsg, e);
166 throw new IllegalArgumentException(errorMsg);
167 } catch (InvocationTargetException e) {
168 final String errorMsg = "Exception occurred in property's getter";
169 log.error(errorMsg, e);
170 throw new IllegalArgumentException(errorMsg);
171 } catch (NoSuchMethodException e) {
172 final String errorMsg = "No property found for name [" +
173 propertyName + "]";
174 log.error(errorMsg, e);
175 throw new IllegalArgumentException(errorMsg);
176 }
177
178 return propertyValue;
179 }
180
181 /***
182 * Returns the name of the property that will be used in the transformation of the bean.
183 *
184 * @return The name of the property that will be used in the transformation of the bean.
185 */
186 public String getPropertyName() {
187 return propertyName;
188 }
189
190 /***
191 * Returns the flag which determines whether <code>null</code> objects in the property path will
192 * genenerate an <code>IllegalArgumentException</code> or not. If set to <code>true</code> then
193 * if any objects in the property path evaluate to <code>null</code> then the
194 * <code>IllegalArgumentException</code> throw by <code>PropertyUtils</code> will be logged but
195 * not rethrown and <code>null</code> will be returned. If set to <code>false</code> then if any
196 * objects in the property path evaluate to <code>null</code> then the
197 * <code>IllegalArgumentException</code> throw by <code>PropertyUtils</code> will be logged and
198 * rethrown.
199 *
200 * @return The flag which determines whether <code>null</code> objects in the property path will
201 * genenerate an <code>IllegalArgumentException</code> or not.
202 */
203 public boolean isIgnoreNull() {
204 return ignoreNull;
205 }
206 }