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BeanUtils provides an easy-to-use but flexible wrapper around reflection and introspection.
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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
 * limitations under the License.
 */
 
package org.apache.commons.beanutils;

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

import java.lang.reflect.InvocationTargetException;


/**
 * Closure that sets a property.
 * 
 * An implementation of org.apache.commons.collections.Closure that updates
 * a specified property on the object provided with a specified value.
 * The BeanPropertyValueChangeClosure constructor takes two parameters which determine
 * what property will be updated and with what value.
 * 

 *    
 *       
 *           public BeanPropertyValueChangeClosure( String propertyName, Object propertyValue )
 *       
 *    
 *    
 *       Will create a Closure that will update an object by setting the property
 *       specified by propertyName to the value specified by propertyValue.
 *    
 * 
 *
 * 
 * Note: Property names can be a simple, nested, indexed, or mapped property as defined by
 * org.apache.commons.beanutils.PropertyUtils.  If any object in the property path
 * specified by propertyName is null then the outcome is based on the
 * value of the ignoreNull attribute.
 *
 * 

 * A typical usage might look like:
 * 
 * // create the closure
 * BeanPropertyValueChangeClosure closure =
 *    new BeanPropertyValueChangeClosure( "activeEmployee", Boolean.TRUE );
 *
 * // update the Collection
 * CollectionUtils.forAllDo( peopleCollection, closure );
 * 
 * 
 *
 * This would take a Collection of person objects and update the
 * activeEmployee property of each object in the Collection to
 * true. Assuming...
 * 

 *    
 *       The top level object in the peopleCollection is an object which represents a
 *       person.
 *    
 *    
 *       The person object has a setActiveEmployee( boolean ) method which updates
 *       the value for the object's activeEmployee property.
 *    
 * 
 *
 * @author Norm Deane
 * @see org.apache.commons.beanutils.PropertyUtils
 * @see org.apache.commons.collections.Closure
 */
public class BeanPropertyValueChangeClosure implements Closure {
   
    /** For logging. */
    private final Log log = LogFactory.getLog(this.getClass());

    /**
     * The name of the property which will be updated when this Closure executes.
     */
    private String propertyName;

    /**
     * The value that the property specified by propertyName
     * will be updated to when this Closure executes.
     */
    private Object propertyValue;

    /**
     * Determines whether null objects in the property path will genenerate an
     * IllegalArgumentException or not. If set to true then if any objects
     * in the property path leading up to the target property evaluate to null then the
     * IllegalArgumentException throw by PropertyUtils will be logged but
     * not rethrown.  If set to false then if any objects in the property path leading
     * up to the target property evaluate to null then the
     * IllegalArgumentException throw by PropertyUtils will be logged and
     * rethrown.
     */
    private boolean ignoreNull;

    /**
     * Constructor which takes the name of the property to be changed, the new value to set
     * the property to, and assumes ignoreNull to be false.
     *
     * @param propertyName The name of the property that will be updated with the value specified by
     * propertyValue.
     * @param propertyValue The value that propertyName will be set to on the target
     * object.
     * @throws IllegalArgumentException If the propertyName provided is null or empty.
     */
    public BeanPropertyValueChangeClosure(String propertyName, Object propertyValue) {
        this(propertyName, propertyValue, false);
    }

    /**
     * Constructor which takes the name of the property to be changed, the new value to set
     * the property to and a boolean which determines whether null objects in the
     * property path will genenerate an IllegalArgumentException or not.
     *
     * @param propertyName The name of the property that will be updated with the value specified by
     * propertyValue.
     * @param propertyValue The value that propertyName will be set to on the target
     * object.
     * @param ignoreNull Determines whether null objects in the property path will
     * genenerate an IllegalArgumentException or not.
     * @throws IllegalArgumentException If the propertyName provided is null or empty.
     */
    public BeanPropertyValueChangeClosure(String propertyName, Object propertyValue, boolean ignoreNull) {
        super();

        if ((propertyName != null) && (propertyName.length() > 0)) {
            this.propertyName = propertyName;
            this.propertyValue = propertyValue;
            this.ignoreNull = ignoreNull;
        } else {
            throw new IllegalArgumentException("propertyName cannot be null or empty");
        }
    }

    /**
     * Updates the target object provided using the property update criteria provided when this
     * BeanPropertyValueChangeClosure was constructed.  If any object in the property
     * path leading up to the target property is null then the outcome will be based on
     * the value of the ignoreNull attribute. By default, ignoreNull is
     * false and would result in an IllegalArgumentException if an object
     * in the property path leading up to the target property is null.
     *
     * @param object The object to be updated.
     * @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 null and
     * ignoreNull is set to false.
     */
    public void execute(Object object) {
       
        try {
            PropertyUtils.setProperty(object, propertyName, propertyValue);
        } catch (IllegalArgumentException e) {
            final String errorMsg = "Unable to execute Closure. 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 = "Property not found";
            IllegalArgumentException iae = new IllegalArgumentException(errorMsg);
            if (!BeanUtils.initCause(iae, e)) {
                log.error(errorMsg, e);
            }
            throw iae;
        }
    }

    /**
     * Returns the name of the property which will be updated when this Closure executes.
     *
     * @return The name of the property which will be updated when this Closure executes.
     */
    public String getPropertyName() {
        return propertyName;
    }

    /**
     * Returns the value that the property specified by propertyName
     * will be updated to when this Closure executes.
     *
     * @return The value that the property specified by propertyName
     * will be updated to when this Closure executes.
     */
    public Object getPropertyValue() {
        return propertyValue;
    }

    /**
     * Returns the flag that determines whether null objects in the property path will
     * genenerate an IllegalArgumentException or not. If set to true then
     * if any objects in the property path leading up to the target property evaluate to
     * null then the IllegalArgumentException throw by
     * PropertyUtils will be logged but not rethrown.  If set to false then
     * if any objects in the property path leading up to the target property evaluate to
     * null then the IllegalArgumentException throw by
     * PropertyUtils will be logged and rethrown.
     *
     * @return The flag that determines whether null objects in the property path will
     * genenerate an IllegalArgumentException or not.
     */
    public boolean isIgnoreNull() {
        return ignoreNull;
    }
}