BeanComparator.java
/*
* 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.beanutils2;
import java.lang.reflect.InvocationTargetException;
import java.util.Comparator;
/**
* <p>
* This comparator compares two beans by the specified bean property. It is also possible to compare beans based on nested, indexed, combined, mapped bean
* properties. Please see the {@link PropertyUtilsBean} documentation for all property name possibilities.
*
* </p>
* <p>
* <strong>Note:</strong> The BeanComparator passes the values of the specified bean property to an internal natural order {@link Comparator}, if no comparator
* is specified in the constructor. If you are comparing two beans based on a property that could contain "null" values, a suitable {@code Comparator} or Apache
* Commons Collection {@code ComparatorChain} should be supplied in the constructor. Note that the passed in {@code Comparator} must be able to handle the
* passed in objects. Because the type of the property to be compared is not known at compile time no type checks can be performed by the compiler. Thus
* {@code ClassCastException} exceptions can be thrown if unexpected property values occur.
* </p>
*
* @param <T> the type of beans to be compared by this {@code Comparator}
* @param <V> the type of property to compare
*/
public class BeanComparator<T, V> implements Comparator<T> {
/**
* A {@link Comparator Comparator} that compares {@link Comparable Comparable} objects.
* <p>
* This Comparator is useful, for example, for enforcing the natural order in custom implementations of {@link java.util.SortedSet SortedSet} and
* {@link java.util.SortedMap SortedMap}.
* </p>
*
* @param <E> the type of objects compared by this comparator
* @see java.util.Collections#reverseOrder()
*/
private static final class NaturalOrderComparator<E extends Comparable<? super E>> implements Comparator<E> {
/** The singleton instance. */
@SuppressWarnings("rawtypes")
public static final NaturalOrderComparator INSTANCE = new NaturalOrderComparator();
/**
* Private constructor to prevent instantiation. Only use INSTANCE.
*/
private NaturalOrderComparator() {
}
/**
* Compare the two {@link Comparable Comparable} arguments. This method is equivalent to:
*
* <pre>
* ((Comparable) obj1).compareTo(obj2)
* </pre>
*/
@Override
public int compare(final E obj1, final E obj2) {
return obj1.compareTo(obj2);
}
@Override
public boolean equals(final Object object) {
return this == object || null != object && object.getClass().equals(this.getClass());
}
@Override
public int hashCode() {
return "NaturalOrderComparator".hashCode();
}
}
private static final long serialVersionUID = 1L;
/** Property. */
private String property;
/** Comparator, untyped. */
private final Comparator<V> comparator;
/**
* <p>
* Constructs a Bean Comparator without a property set.
* </p>
* <p>
* <strong>Note</strong> that this is intended to be used only in bean-centric environments.
* </p>
* <p>
* Until {@link #setProperty} is called with a non-null value. this comparator will compare the Objects only.
* </p>
*/
public BeanComparator() {
this(null);
}
/**
* <p>
* Constructs a property-based comparator for beans. This compares two beans by the property specified in the property parameter. This constructor creates a
* {@code BeanComparator} that uses a {@code ComparableComparator} to compare the property values.
* </p>
*
* <p>
* Passing "null" to this constructor will cause the BeanComparator to compare objects based on natural order, that is {@link Comparable}.
* </p>
*
* @param property String Name of a bean property, which may contain the name of a simple, nested, indexed, mapped, or combined property. See
* {@link PropertyUtilsBean} for property query language syntax. If the property passed in is null then the actual objects will be compared
*/
public BeanComparator(final String property) {
this(property, NaturalOrderComparator.INSTANCE);
}
/**
* Constructs a property-based comparator for beans. This constructor creates a BeanComparator that uses the supplied Comparator to compare the property
* values.
*
* @param property Name of a bean property, can contain the name of a simple, nested, indexed, mapped, or combined property. See {@link PropertyUtilsBean}
* for property query language syntax.
* @param comparator BeanComparator will pass the values of the specified bean property to this Comparator. If your bean property is not a comparable or
* contains null values, a suitable comparator may be supplied in this constructor.
*/
public BeanComparator(final String property, final Comparator<V> comparator) {
setProperty(property);
this.comparator = comparator != null ? comparator : NaturalOrderComparator.INSTANCE;
}
/**
* Compare two JavaBeans by their shared property. If {@link #getProperty} is null then the actual objects will be compared.
*
* @param o1 Object The first bean to get data from to compare against
* @param o2 Object The second bean to get data from to compare
* @return int negative or positive based on order
*/
@Override
public int compare(final T o1, final T o2) {
if (property == null) {
// compare the actual objects
return internalCompare(o1, o2);
}
try {
final Object value1 = PropertyUtils.getProperty(o1, property);
final Object value2 = PropertyUtils.getProperty(o2, property);
return internalCompare(value1, value2);
} catch (final NoSuchMethodException | IllegalAccessException | InvocationTargetException e) {
throw new RuntimeException(e.getClass().getSimpleName() + ": " + e.toString());
}
}
/**
* Two {@code BeanComparator}'s are equals if and only if the wrapped comparators and the property names to be compared are equal.
*
* @param o Comparator to compare to
* @return whether the comparators are equal or not
*/
@Override
public boolean equals(final Object o) {
if (this == o) {
return true;
}
if (!(o instanceof BeanComparator)) {
return false;
}
final BeanComparator<?, ?> beanComparator = (BeanComparator<?, ?>) o;
if (!comparator.equals(beanComparator.comparator)) {
return false;
}
if (property == null) {
return beanComparator.property == null;
}
return property.equals(beanComparator.property);
}
/**
* Gets the Comparator being used to compare beans.
*
* @return the Comparator being used to compare beans
*/
public Comparator<V> getComparator() {
return comparator;
}
/**
* Gets the property attribute of the BeanComparator
*
* @return String method name to call to compare. A null value indicates that the actual objects will be compared
*/
public String getProperty() {
return property;
}
/**
* Hashcode compatible with equals.
*
* @return the hash code for this comparator
*/
@Override
public int hashCode() {
return comparator.hashCode();
}
/**
* Compares the given values using the internal {@code Comparator}. <em>Note</em>: This comparison cannot be performed in a type-safe way; so
* {@code ClassCastException} exceptions may be thrown.
*
* @param val1 the first value to be compared
* @param val2 the second value to be compared
* @return the result of the comparison
*/
@SuppressWarnings({ "unchecked", "rawtypes" })
private int internalCompare(final Object val1, final Object val2) {
return ((Comparator) comparator).compare(val1, val2);
}
/**
* Sets the method to be called to compare two JavaBeans
*
* @param property String method name to call to compare If the property passed in is null then the actual objects will be compared
*/
public void setProperty(final String property) {
this.property = property;
}
}