BeanToPropertyValueTransformer.java
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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}.
*
* @param object The object to be transformed.
* @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;
}
}