code/spi-support/src/main/java/org/apache/tamaya/spisupport/PropertyFilterComparator.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.tamaya.spisupport;

import org.apache.tamaya.spi.PropertyFilter;
import org.apache.tamaya.spi.ServiceContext;

import javax.annotation.Priority;
import java.io.Serializable;
import java.util.Comparator;

/**
 * Comparator for {@link PropertyFilter}s based on their priority annotations.
 */
public final class PropertyFilterComparator implements Comparator<PropertyFilter>, Serializable {

    private static final long serialVersionUID = 1L;

    private static final PropertyFilterComparator INSTANCE = new PropertyFilterComparator();

    /**
     * Get the shared instance of the comparator.
     * @return the shared instance, never null.
     */
    public static PropertyFilterComparator getInstance(){
        return INSTANCE;
    }

    private PropertyFilterComparator(){}

    /**
     * Compare 2 filters for ordering the filter chain.
     *
     * @param filter1 the first filter
     * @param filter2 the second filter
     * @return the comparison result
     */
    private int comparePropertyFilters(PropertyFilter filter1, PropertyFilter filter2) {
        int ord1 = 0;
        int ord2 = 0;

        if(ServiceContext.PRIORITY_ANNOTATION_AVAILABLE) {
            Priority prio1 = filter1.getClass().getAnnotation(Priority.class);
            Priority prio2 = filter2.getClass().getAnnotation(Priority.class);
            if(prio1!=null) {
                ord1 = prio1.value();
            }
            if(prio2!=null) {
                ord2 = prio2.value();
            }
        }
        if (ord1 < ord2) {
            return -1;
        } else if (ord1 > ord2) {
            return 1;
        } else {
            return filter1.getClass().getName().compareTo(filter2.getClass().getName());
        }
    }

    @Override
    public int compare(PropertyFilter filter1, PropertyFilter filter2) {
        return comparePropertyFilters(filter1, filter2);
    }
}