001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017
018package org.apache.commons.beanutils2;
019
020import java.lang.reflect.InvocationTargetException;
021import java.util.function.Function;
022
023import org.apache.commons.logging.Log;
024import org.apache.commons.logging.LogFactory;
025
026/**
027 * <p>
028 * {@code Transformer} that outputs a property value.
029 * </p>
030 *
031 * <p>
032 * An implementation of {@link java.util.function.Function} that transforms the object provided by returning the value of a specified property of the object.
033 * The constructor for {@code BeanToPropertyValueTransformer} requires the name of the property that will be used in the transformation. The property can be a
034 * simple, nested, indexed, or mapped property as defined by {@code org.apache.commons.beanutils2.PropertyUtils}. If any object in the property path specified
035 * by {@code propertyName</code> is <code>null} then the
036 * outcome is based on the value of the {@code ignoreNull} attribute.
037 * </p>
038 *
039 * <p>
040 * A typical usage might look like:
041 * </p>
042 * <pre>{@code
043 * // create the transformer
044 * BeanToPropertyValueTransformer transformer = new BeanToPropertyValueTransformer( "person.address.city" );
045 *
046 * // transform the Collection
047 * Collection peoplesCities = CollectionUtils.collect( peopleCollection, transformer );
048 * }</pre>
049 *
050 * <p>
051 * This would take a {@code Collection</code> of person objects and return a <code>Collection} of objects which represents the cities in which each person
052 * lived. Assuming...
053 * <ul>
054 * <li>The top level object in the {@code peopleCollection} is an object which represents a person.</li>
055 * <li>The person object has a {@code getAddress()} method which returns an object which represents a person's address.</li>
056 * <li>The address object has a {@code getCity()} method which returns an object which represents the city in which a person lives.</li>
057 * </ul>
058 *
059 * @param <T> the type of the input to the function
060 * @param <R> the type of the result of the function
061 * @see org.apache.commons.beanutils2.PropertyUtils
062 * @see java.util.function.Function
063 */
064public class BeanToPropertyValueTransformer<T, R> implements Function<T, R> {
065
066    /** For logging. Each subclass gets its own log instance. */
067    private final Log log = LogFactory.getLog(this.getClass());
068
069    /** The name of the property that will be used in the transformation of the object. */
070    private final String propertyName;
071
072    /**
073     * <p>
074     * Should null objects on the property path throw an {@code IllegalArgumentException}?
075     * </p>
076     * <p>
077     * Determines whether {@code null} objects in the property path will generate an
078     * {@code IllegalArgumentException</code> or not. If set to <code>true} then if any objects
079     * in the property path evaluate to {@code null} then the
080     * {@code IllegalArgumentException</code> throw by <code>PropertyUtils} will be logged but
081     * not re-thrown and {@code null</code> will be returned.  If set to <code>false} then if any
082     * objects in the property path evaluate to {@code null} then the
083     * {@code IllegalArgumentException</code> throw by <code>PropertyUtils} will be logged and re-thrown.
084     * </p>
085     */
086    private final boolean ignoreNull;
087
088    /**
089     * Constructs a Transformer which does not ignore nulls. Constructor which takes the name of the property that will be used in the transformation and
090     * assumes {@code ignoreNull</code> to be <code>false}.
091     *
092     * @param propertyName The name of the property that will be used in the transformation.
093     * @throws IllegalArgumentException If the {@code propertyName</code> is <code>null} or empty.
094     */
095    public BeanToPropertyValueTransformer(final String propertyName) {
096        this(propertyName, false);
097    }
098
099    /**
100     * Constructs a Transformer and sets ignoreNull. Constructor which takes the name of the property that will be used in the transformation and a boolean
101     * which determines whether {@code null} objects in the property path will generate an {@code IllegalArgumentException} or not.
102     *
103     * @param propertyName The name of the property that will be used in the transformation.
104     * @param ignoreNull   Determines whether {@code null} objects in the property path will generate an {@code IllegalArgumentException} or not.
105     * @throws IllegalArgumentException If the {@code propertyName</code> is <code>null} or empty.
106     */
107    public BeanToPropertyValueTransformer(final String propertyName, final boolean ignoreNull) {
108        if (propertyName == null || propertyName.isEmpty()) {
109            throw new IllegalArgumentException("propertyName cannot be null or empty");
110        }
111        this.propertyName = propertyName;
112        this.ignoreNull = ignoreNull;
113    }
114
115    /**
116     * Returns the value of the property named in the transformer's constructor for the object provided. If any object in the property path leading up to the
117     * target property is {@code null</code> then the outcome will be based on the value of the <code>ignoreNull}
118     * attribute. By default, {@code ignoreNull</code> is <code>false} and would result in an
119     * {@code IllegalArgumentException} if an object in the property path leading up to the
120     * target property is {@code null}.
121     *
122     * &#64;param object The object to be transformed.
123     * &#64;return The value of the property named in the transformer's constructor for the object
124     * provided.
125     * @throws IllegalArgumentException If an IllegalAccessException, InvocationTargetException, or
126     * NoSuchMethodException is thrown when trying to access the property specified on the object
127     * provided. Or if an object in the property path provided is {@code null} and
128     * {@code ignoreNull</code> is set to <code>false}.
129     */
130    @Override
131    public R apply(final T object) {
132        R propertyValue = null;
133        try {
134            propertyValue = (R) PropertyUtils.getProperty(object, propertyName);
135        } catch (final IllegalArgumentException e) {
136            final String errorMsg = "Problem during transformation. Null value encountered in property path...";
137            if (!ignoreNull) {
138                throw new IllegalArgumentException(errorMsg, e);
139            }
140            log.warn(errorMsg, e);
141        } catch (final IllegalAccessException e) {
142            final String errorMsg = "Unable to access the property provided.";
143            throw new IllegalArgumentException(errorMsg, e);
144        } catch (final InvocationTargetException e) {
145            final String errorMsg = "Exception occurred in property's getter";
146            throw new IllegalArgumentException(errorMsg, e);
147        } catch (final NoSuchMethodException e) {
148            final String errorMsg = "No property found for name [" + propertyName + "]";
149            throw new IllegalArgumentException(errorMsg, e);
150        }
151
152        return propertyValue;
153    }
154
155    /**
156     * Returns the name of the property that will be used in the transformation of the bean.
157     *
158     * @return The name of the property that will be used in the transformation of the bean.
159     */
160    public String getPropertyName() {
161        return propertyName;
162    }
163
164    /**
165     * Returns the flag which determines whether {@code null} objects in the property path will generate an
166     * {@code IllegalArgumentException</code> or not. If set to <code>true} then
167     * if any objects in the property path evaluate to {@code null} then the
168     * {@code IllegalArgumentException</code> throw by <code>PropertyUtils} will be logged but
169     * not re-thrown and {@code null</code> will be returned.  If set to <code>false} then if any
170     * objects in the property path evaluate to {@code null} then the
171     * {@code IllegalArgumentException</code> throw by <code>PropertyUtils} will be logged and re-thrown.
172     *
173     * @return The flag which determines whether {@code null} objects in the property path will generate an {@code IllegalArgumentException} or not.
174     */
175    public boolean isIgnoreNull() {
176        return ignoreNull;
177    }
178}