org.apache.commons.beanutils.BeanComparator Maven / Gradle / Ivy
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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 java.io.Serializable;
import java.lang.reflect.InvocationTargetException;
import java.util.Comparator;
import org.apache.commons.collections.comparators.ComparableComparator;
/**
*
* 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.
*
*
* Note: The BeanComparator passes the values of the specified
* bean property to a ComparableComparator, 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 Comparator
* or 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.
*
*
* @param the type of beans to be compared by this {@code Comparator}
* @version $Id$
*/
public class BeanComparator implements Comparator, Serializable {
private String property;
private final Comparator comparator;
/**
* Constructs a Bean Comparator without a property set.
*
* Note that this is intended to be used
* only in bean-centric environments.
*
* Until {@link #setProperty} is called with a non-null value.
* this comparator will compare the Objects only.
*
*/
public BeanComparator() {
this( null );
}
/**
* Constructs a property-based comparator for beans.
* This compares two beans by the property
* specified in the property parameter. This constructor creates
* a BeanComparator that uses a ComparableComparator
* to compare the property values.
*
*
* Passing "null" to this constructor will cause the BeanComparator
* to compare objects based on natural order, that is
* java.lang.Comparable.
*
*
* @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, ComparableComparator.getInstance() );
}
/**
* 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 comparator ) {
setProperty( property );
if (comparator != null) {
this.comparator = comparator;
} else {
this.comparator = ComparableComparator.getInstance();
}
}
/**
* 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;
}
/**
* 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;
}
/**
* Gets the Comparator being used to compare beans.
*
* @return the Comparator being used to compare beans
*/
public Comparator getComparator() {
return comparator;
}
/**
* 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
*/
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 IllegalAccessException iae ) {
throw new RuntimeException( "IllegalAccessException: " + iae.toString() );
}
catch ( final InvocationTargetException ite ) {
throw new RuntimeException( "InvocationTargetException: " + ite.toString() );
}
catch ( final NoSuchMethodException nsme ) {
throw new RuntimeException( "NoSuchMethodException: " + nsme.toString() );
}
}
/**
* Two 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 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)
{
if (!property.equals(beanComparator.property)) {
return false;
}
}
else
{
return (beanComparator.property == null);
}
return true;
}
/**
* Hashcode compatible with equals.
* @return the hash code for this comparator
*/
@Override
public int hashCode() {
int result;
result = comparator.hashCode();
return result;
}
/**
* Compares the given values using the internal {@code Comparator}.
* Note: 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
*/
private int internalCompare(final Object val1, final Object val2) {
@SuppressWarnings("rawtypes")
final
// to make the compiler happy
Comparator c = comparator;
return c.compare(val1, val2);
}
}