Java tutorial
/* * 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 * limitations under the License. */ package org.apache.commons.beanutils; import org.apache.commons.collections.Transformer; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; import java.lang.reflect.InvocationTargetException; /** * <p><code>Transformer</code> that outputs a property value.</p> * * <p>An implementation of <code>org.apache.commons.collections.Transformer</code> that transforms * the object provided by returning the value of a specified property of the object. The * constructor for <code>BeanToPropertyValueTransformer</code> 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.beanutils.PropertyUtils</code>. If any * object in the property path specified by <code>propertyName</code> is <code>null</code> then the * outcome is based on the value of the <code>ignoreNull</code> attribute. * </p> * * <p> * A typical usage might look like: * <code><pre> * // create the transformer * BeanToPropertyValueTransformer transformer = new BeanToPropertyValueTransformer( "person.address.city" ); * * // transform the Collection * Collection peoplesCities = CollectionUtils.collect( peopleCollection, transformer ); * </pre></code> * </p> * * <p> * This would take a <code>Collection</code> of person objects and return a <code>Collection</code> * of objects which represents the cities in which each person lived. Assuming... * <ul> * <li> * The top level object in the <code>peeopleCollection</code> is an object which represents a * person. * </li> * <li> * The person object has a <code>getAddress()</code> method which returns an object which * represents a person's address. * </li> * <li> * The address object has a <code>getCity()</code> method which returns an object which * represents the city in which a person lives. * </li> * </ul> * * @author Norm Deane * @see org.apache.commons.beanutils.PropertyUtils * @see org.apache.commons.collections.Transformer */ public class BeanToPropertyValueTransformer implements Transformer { /** For logging. */ private final Log log = LogFactory.getLog(this.getClass()); /** The name of the property that will be used in the transformation of the object. */ private String propertyName; /** * <p>Should null objects on the property path throw an <code>IllegalArgumentException</code>?</p> * <p> * Determines whether <code>null</code> objects in the property path will genenerate an * <code>IllegalArgumentException</code> or not. If set to <code>true</code> then if any objects * in the property path evaluate to <code>null</code> then the * <code>IllegalArgumentException</code> throw by <code>PropertyUtils</code> will be logged but * not rethrown and <code>null</code> will be returned. If set to <code>false</code> then if any * objects in the property path evaluate to <code>null</code> then the * <code>IllegalArgumentException</code> throw by <code>PropertyUtils</code> will be logged and * rethrown. * </p> */ private 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</code>. * * @param propertyName The name of the property that will be used in the transformation. * @throws IllegalArgumentException If the <code>propertyName</code> is <code>null</code> or * empty. */ public BeanToPropertyValueTransformer(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</code> objects in the property path will * genenerate an <code>IllegalArgumentException</code> or not. * * @param propertyName The name of the property that will be used in the transformation. * @param ignoreNull Determines whether <code>null</code> objects in the property path will * genenerate an <code>IllegalArgumentException</code> or not. * @throws IllegalArgumentException If the <code>propertyName</code> is <code>null</code> or * empty. */ public BeanToPropertyValueTransformer(String propertyName, boolean ignoreNull) { super(); if ((propertyName != null) && (propertyName.length() > 0)) { this.propertyName = propertyName; this.ignoreNull = ignoreNull; } else { throw new IllegalArgumentException("propertyName cannot be null or empty"); } } /** * 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</code> * attribute. By default, <code>ignoreNull</code> is <code>false</code> and would result in an * <code>IllegalArgumentException</code> if an object in the property path leading up to the * target property is <code>null</code>. * * @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</code> and * <code>ignoreNull</code> is set to <code>false</code>. */ public Object transform(Object object) { Object propertyValue = null; try { propertyValue = PropertyUtils.getProperty(object, propertyName); } catch (IllegalArgumentException e) { final String errorMsg = "Problem during transformation. Null value encountered in property path..."; if (ignoreNull) { log.warn("WARNING: " + errorMsg + e); } else { IllegalArgumentException iae = new IllegalArgumentException(errorMsg); if (!BeanUtils.initCause(iae, e)) { log.error(errorMsg, e); } throw iae; } } catch (IllegalAccessException e) { final String errorMsg = "Unable to access the property provided."; IllegalArgumentException iae = new IllegalArgumentException(errorMsg); if (!BeanUtils.initCause(iae, e)) { log.error(errorMsg, e); } throw iae; } catch (InvocationTargetException e) { final String errorMsg = "Exception occurred in property's getter"; IllegalArgumentException iae = new IllegalArgumentException(errorMsg); if (!BeanUtils.initCause(iae, e)) { log.error(errorMsg, e); } throw iae; } catch (NoSuchMethodException e) { final String errorMsg = "No property found for name [" + propertyName + "]"; IllegalArgumentException iae = new IllegalArgumentException(errorMsg); if (!BeanUtils.initCause(iae, e)) { log.error(errorMsg, e); } throw iae; } 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</code> objects in the property path will * genenerate an <code>IllegalArgumentException</code> or not. If set to <code>true</code> then * if any objects in the property path evaluate to <code>null</code> then the * <code>IllegalArgumentException</code> throw by <code>PropertyUtils</code> will be logged but * not rethrown and <code>null</code> will be returned. If set to <code>false</code> then if any * objects in the property path evaluate to <code>null</code> then the * <code>IllegalArgumentException</code> throw by <code>PropertyUtils</code> will be logged and * rethrown. * * @return The flag which determines whether <code>null</code> objects in the property path will * genenerate an <code>IllegalArgumentException</code> or not. */ public boolean isIgnoreNull() { return ignoreNull; } }