BeanToPropertyValueTransformer

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 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
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package org.apache.commons.beanutils2;

import java.lang.reflect.InvocationTargetException;
import java.util.function.Function;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

/**
 * <p>
 * {@code Transformer} that outputs a property value.
 * </p>
 *
 * <p>
 * An implementation of {@link java.util.function.Function} that transforms the object provided by returning the value of a specified property of the object.
 * The constructor for {@code BeanToPropertyValueTransformer} requires the name of the property that will be used in the transformation. The property can be a
 * simple, nested, indexed, or mapped property as defined by {@code org.apache.commons.beanutils2.PropertyUtils}. If any object in the property path specified
 * by {@code propertyName</code> is <code>null} then the
 * outcome is based on the value of the {@code ignoreNull} attribute.
 * </p>
 *
 * <p>
 * A typical usage might look like:
 * </p>
 * <pre>{@code
 * // create the transformer
 * BeanToPropertyValueTransformer transformer = new BeanToPropertyValueTransformer( "person.address.city" );
 *
 * // transform the Collection
 * Collection peoplesCities = CollectionUtils.collect( peopleCollection, transformer );
 * }</pre>
 *
 * <p>
 * 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
 * lived. Assuming...
 * <ul>
 * <li>The top level object in the {@code peopleCollection} is an object which represents a person.</li>
 * <li>The person object has a {@code getAddress()} method which returns an object which represents a person's address.</li>
 * <li>The address object has a {@code getCity()} method which returns an object which represents the city in which a person lives.</li>
 * </ul>
 *
 * @param <T> the type of the input to the function
 * @param <R> the type of the result of the function
 * @see org.apache.commons.beanutils2.PropertyUtils
 * @see java.util.function.Function
 */
public class BeanToPropertyValueTransformer<T, R> implements Function<T, R> {

    /** For logging. Each subclass gets its own log instance. */
    private final Log log = LogFactory.getLog(this.getClass());

    /** The name of the property that will be used in the transformation of the object. */
    private final String propertyName;

    /**
     * <p>
     * Should null objects on the property path throw an {@code IllegalArgumentException}?
     * </p>
     * <p>
     * Determines whether {@code null} objects in the property path will generate an
     * {@code IllegalArgumentException</code> or not. If set to <code>true} then if any objects
     * in the property path evaluate to {@code null} then the
     * {@code IllegalArgumentException</code> throw by <code>PropertyUtils} will be logged but
     * not re-thrown and {@code null</code> will be returned.  If set to <code>false} then if any
     * objects in the property path evaluate to {@code null} then the
     * {@code IllegalArgumentException</code> throw by <code>PropertyUtils} will be logged and re-thrown.
     * </p>
     */
    private final boolean ignoreNull;

    /**
     * Constructs a Transformer which does not ignore nulls. Constructor which takes the name of the property that will be used in the transformation and
     * assumes {@code ignoreNull</code> to be <code>false}.
     *
     * @param propertyName The name of the property that will be used in the transformation.
     * @throws IllegalArgumentException If the {@code propertyName</code> is <code>null} or empty.
     */
    public BeanToPropertyValueTransformer(final String propertyName) {
        this(propertyName, false);
    }

    /**
     * Constructs a Transformer and sets ignoreNull. Constructor which takes the name of the property that will be used in the transformation and a boolean
     * which determines whether {@code null} objects in the property path will generate an {@code IllegalArgumentException} or not.
     *
     * @param propertyName The name of the property that will be used in the transformation.
     * @param ignoreNull   Determines whether {@code null} objects in the property path will generate an {@code IllegalArgumentException} or not.
     * @throws IllegalArgumentException If the {@code propertyName</code> is <code>null} or empty.
     */
    public BeanToPropertyValueTransformer(final String propertyName, final boolean ignoreNull) {
        if (propertyName == null || propertyName.isEmpty()) {
            throw new IllegalArgumentException("propertyName cannot be null or empty");
        }
        this.propertyName = propertyName;
        this.ignoreNull = ignoreNull;
    }

    /**
     * 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
     * target property is {@code null</code> then the outcome will be based on the value of the <code>ignoreNull}
     * attribute. By default, {@code ignoreNull</code> is <code>false} and would result in an
     * {@code IllegalArgumentException} if an object in the property path leading up to the
     * target property is {@code null}.
     *
     * &#64;param object The object to be transformed.
     * &#64;return The value of the property named in the transformer's constructor for the object
     * provided.
     * @throws IllegalArgumentException If an IllegalAccessException, InvocationTargetException, or
     * NoSuchMethodException is thrown when trying to access the property specified on the object
     * provided. Or if an object in the property path provided is {@code null} and
     * {@code ignoreNull</code> is set to <code>false}.
     */
    @Override
    public R apply(final T object) {
        R propertyValue = null;
        try {
            propertyValue = (R) PropertyUtils.getProperty(object, propertyName);
        } catch (final IllegalArgumentException e) {
            final String errorMsg = "Problem during transformation. Null value encountered in property path...";
            if (!ignoreNull) {
                throw new IllegalArgumentException(errorMsg, e);
            }
            log.warn(errorMsg, e);
        } catch (final IllegalAccessException e) {
            final String errorMsg = "Unable to access the property provided.";
            throw new IllegalArgumentException(errorMsg, e);
        } catch (final InvocationTargetException e) {
            final String errorMsg = "Exception occurred in property's getter";
            throw new IllegalArgumentException(errorMsg, e);
        } catch (final NoSuchMethodException e) {
            final String errorMsg = "No property found for name [" + propertyName + "]";
            throw new IllegalArgumentException(errorMsg, e);
        }

        return propertyValue;
    }

    /**
     * Returns the name of the property that will be used in the transformation of the bean.
     *
     * @return The name of the property that will be used in the transformation of the bean.
     */
    public String getPropertyName() {
        return propertyName;
    }

    /**
     * Returns the flag which determines whether {@code null} objects in the property path will generate an
     * {@code IllegalArgumentException</code> or not. If set to <code>true} then
     * if any objects in the property path evaluate to {@code null} then the
     * {@code IllegalArgumentException</code> throw by <code>PropertyUtils} will be logged but
     * not re-thrown and {@code null</code> will be returned.  If set to <code>false} then if any
     * objects in the property path evaluate to {@code null} then the
     * {@code IllegalArgumentException</code> throw by <code>PropertyUtils} will be logged and re-thrown.
     *
     * @return The flag which determines whether {@code null} objects in the property path will generate an {@code IllegalArgumentException} or not.
     */
    public boolean isIgnoreNull() {
        return ignoreNull;
    }
}