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Apache Commons 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
 *
 *      https://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.beanutils2;

import java.lang.reflect.InvocationTargetException;
import java.util.Objects;
import java.util.function.Predicate;

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

/**
 * 
 * {@code Predicate} that evaluates a property value against a specified value.
 * 
 * 
 * An implementation of {@link java.util.function.Predicate} that evaluates a property value on the object provided against a specified value and returns
 * {@code true} if equal; {@code false} otherwise. The {@code BeanPropertyValueEqualsPredicate} constructor takes two parameters which determine what property
 * will be evaluated on the target object and what its expected value should be.
 * 
 * 
 *  {@code public BeanPropertyValueEqualsPredicate( String propertyName, Object propertyValue )} 
 * Will create a {@code Predicate} that will evaluate the target object and return
 * {@code true if the property specified by propertyName} has a value which
 *       is equal to the value specified by {@code propertyValue}. Or return
 *       {@code false} otherwise.
 *    

 * 

 * 
 * Note: Property names 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 is null} then the outcome is based on the
 * value of the {@code ignoreNull} attribute.
 * 

 * 
 * A typical usage might look like:
 * 
 * {@code
 * // create the closure
 * BeanPropertyValueEqualsPredicate predicate =
 *    new BeanPropertyValueEqualsPredicate( "activeEmployee", Boolean.FALSE );
 *
 * // filter the Collection
 * CollectionUtils.filter( peopleCollection, predicate );
 * }
 * 
 * This would take a {@code Collection} of person objects and filter out any people whose
 * {@code activeEmployee property is false}. Assuming...
 * 

 * 
 *    
 *       The top level object in the {@code peopleCollection} is an object which represents a
 *       person.
 *    
 *    
 *       The person object has a {@code getActiveEmployee()} method which returns
 *       the boolean value for the object's {@code activeEmployee} property.
 *    
 * 
 * 
 * Another typical usage might look like:
 * 
 * {@code
 * // create the closure
 * BeanPropertyValueEqualsPredicate predicate =
 *    new BeanPropertyValueEqualsPredicate( "personId", "456-12-1234" );
 *
 * // search the Collection
 * CollectionUtils.find( peopleCollection, predicate );
 * }
 * 
 * This would search a {@code Collection} of person objects and return the first object whose
 * {@code personId property value equals 456-12-1234}. Assuming...
 * 

 * 
 * The top level object in the {@code peopleCollection} is an object which represents a person.
 * The person object has a {@code getPersonId()} method which returns the value for the object's {@code personId} property.
 * 
 *
 * @param  The type of the input to the predicate.
 * @param  The property value type.
 * @see org.apache.commons.beanutils2.PropertyUtils
 * @see java.util.function.Predicate
 */
public class BeanPropertyValueEqualsPredicate implements Predicate {

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

    /**
     * The name of the property which will be evaluated when this {@code Predicate} is executed.
     */
    private final String propertyName;

    /**
     * The value that the property specified by {@code propertyName} will be compared to when this {@code Predicate} executes.
     */
    private final V propertyValue;

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

     */
    private final boolean ignoreNull;

    /**
     * Constructor which takes the name of the property, its expected value to be used in evaluation, and assumes {@code ignoreNull to be false}.
     *
     * @param propertyName  The name of the property that will be evaluated against the expected value.
     * @param propertyValue The value to use in object evaluation.
     * @throws IllegalArgumentException If the property name provided is null or empty.
     */
    public BeanPropertyValueEqualsPredicate(final String propertyName, final V propertyValue) {
        this(propertyName, propertyValue, false);
    }

    /**
     * Constructor which takes the name of the property, its expected value to be used in evaluation, 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 evaluated against the expected value.
     * @param propertyValue The value to use in object evaluation.
     * @param ignoreNull    Determines whether {@code null} objects in the property path will generate an {@code IllegalArgumentException} or not.
     * @throws IllegalArgumentException If the property name provided is null or empty.
     */
    public BeanPropertyValueEqualsPredicate(final String propertyName, final V propertyValue, final boolean ignoreNull) {
        if (propertyName == null || propertyName.isEmpty()) {
            throw new IllegalArgumentException("propertyName cannot be null or empty");
        }
        this.propertyName = propertyName;
        this.propertyValue = propertyValue;
        this.ignoreNull = ignoreNull;
    }

    /**
     * Utility method which evaluates whether the actual property value equals the expected property value.
     *
     * @param expected The expected value.
     * @param actual   The actual value.
     * @return True if they are equal; false otherwise.
     */
    protected boolean evaluateValue(final V expected, final Object actual) {
        return Objects.equals(expected, actual);
    }

    /**
     * Returns the name of the property which will be evaluated when this {@code Predicate} is executed.
     *
     * @return The name of the property which will be evaluated when this {@code Predicate} is executed.
     */
    public String getPropertyName() {
        return propertyName;
    }

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

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

    /**
     * Evaluates the object provided against the criteria specified when this {@code BeanPropertyValueEqualsPredicate} was constructed. Equality is based on
     * either reference or logical equality as defined by the property object's equals method. If any object in the property path leading up to the target
     * property is {@code null} then the outcome will be based on the value of the {@code ignoreNull} attribute. By default,
     * {@code ignoreNull is 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 evaluated.
     * @return True if the object provided meets all the criteria for this {@code Predicate};
     * false otherwise.
     * @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 is set to false}.
     */
    @Override
    public boolean test(final T object) {

        boolean evaluation = false;

        try {
            evaluation = evaluateValue(propertyValue, PropertyUtils.getProperty(object, propertyName));
        } catch (final IllegalArgumentException e) {
            final String errorMsg = "Problem during evaluation. 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 = "Property not found.";
            throw new IllegalArgumentException(errorMsg, e);
        }

        return evaluation;
    }
}