org.springframework.beans.support.PropertyComparator.java Source code

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Here is the source code for org.springframework.beans.support.PropertyComparator.java

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/*
 * Copyright 2002-2018 the original author or authors.
 *
 * Licensed 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.springframework.beans.support;

import java.util.Arrays;
import java.util.Comparator;
import java.util.List;

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

import org.springframework.beans.BeanWrapperImpl;
import org.springframework.beans.BeansException;
import org.springframework.lang.Nullable;
import org.springframework.util.StringUtils;

/**
 * PropertyComparator performs a comparison of two beans,
 * evaluating the specified bean property via a BeanWrapper.
 *
 * @author Juergen Hoeller
 * @author Jean-Pierre Pawlak
 * @since 19.05.2003
 * @param <T> the type of objects that may be compared by this comparator
 * @see org.springframework.beans.BeanWrapper
 */
public class PropertyComparator<T> implements Comparator<T> {

    protected final Log logger = LogFactory.getLog(getClass());

    private final SortDefinition sortDefinition;

    private final BeanWrapperImpl beanWrapper = new BeanWrapperImpl(false);

    /**
     * Create a new PropertyComparator for the given SortDefinition.
     * @see MutableSortDefinition
     */
    public PropertyComparator(SortDefinition sortDefinition) {
        this.sortDefinition = sortDefinition;
    }

    /**
     * Create a PropertyComparator for the given settings.
     * @param property the property to compare
     * @param ignoreCase whether upper and lower case in String values should be ignored
     * @param ascending whether to sort ascending (true) or descending (false)
     */
    public PropertyComparator(String property, boolean ignoreCase, boolean ascending) {
        this.sortDefinition = new MutableSortDefinition(property, ignoreCase, ascending);
    }

    /**
     * Return the SortDefinition that this comparator uses.
     */
    public final SortDefinition getSortDefinition() {
        return this.sortDefinition;
    }

    @Override
    @SuppressWarnings("unchecked")
    public int compare(T o1, T o2) {
        Object v1 = getPropertyValue(o1);
        Object v2 = getPropertyValue(o2);
        if (this.sortDefinition.isIgnoreCase() && (v1 instanceof String) && (v2 instanceof String)) {
            v1 = ((String) v1).toLowerCase();
            v2 = ((String) v2).toLowerCase();
        }

        int result;

        // Put an object with null property at the end of the sort result.
        try {
            if (v1 != null) {
                result = (v2 != null ? ((Comparable<Object>) v1).compareTo(v2) : -1);
            } else {
                result = (v2 != null ? 1 : 0);
            }
        } catch (RuntimeException ex) {
            if (logger.isDebugEnabled()) {
                logger.debug("Could not sort objects [" + o1 + "] and [" + o2 + "]", ex);
            }
            return 0;
        }

        return (this.sortDefinition.isAscending() ? result : -result);
    }

    /**
     * Get the SortDefinition's property value for the given object.
     * @param obj the object to get the property value for
     * @return the property value
     */
    @Nullable
    private Object getPropertyValue(Object obj) {
        // If a nested property cannot be read, simply return null
        // (similar to JSTL EL). If the property doesn't exist in the
        // first place, let the exception through.
        try {
            this.beanWrapper.setWrappedInstance(obj);
            return this.beanWrapper.getPropertyValue(this.sortDefinition.getProperty());
        } catch (BeansException ex) {
            logger.debug("PropertyComparator could not access property - treating as null for sorting", ex);
            return null;
        }
    }

    /**
     * Sort the given List according to the given sort definition.
     * <p>Note: Contained objects have to provide the given property
     * in the form of a bean property, i.e. a getXXX method.
     * @param source the input List
     * @param sortDefinition the parameters to sort by
     * @throws java.lang.IllegalArgumentException in case of a missing propertyName
     */
    public static void sort(List<?> source, SortDefinition sortDefinition) throws BeansException {
        if (StringUtils.hasText(sortDefinition.getProperty())) {
            source.sort(new PropertyComparator<>(sortDefinition));
        }
    }

    /**
     * Sort the given source according to the given sort definition.
     * <p>Note: Contained objects have to provide the given property
     * in the form of a bean property, i.e. a getXXX method.
     * @param source input source
     * @param sortDefinition the parameters to sort by
     * @throws java.lang.IllegalArgumentException in case of a missing propertyName
     */
    public static void sort(Object[] source, SortDefinition sortDefinition) throws BeansException {
        if (StringUtils.hasText(sortDefinition.getProperty())) {
            Arrays.sort(source, new PropertyComparator<>(sortDefinition));
        }
    }

}