001/* 002 * Licensed to the Apache Software Foundation (ASF) under one or more 003 * contributor license agreements. See the NOTICE file distributed with 004 * this work for additional information regarding copyright ownership. 005 * The ASF licenses this file to You under the Apache license, Version 2.0 006 * (the "License"); you may not use this file except in compliance with 007 * the License. You may obtain a copy of the License at 008 * 009 * http://www.apache.org/licenses/LICENSE-2.0 010 * 011 * Unless required by applicable law or agreed to in writing, software 012 * distributed under the License is distributed on an "AS IS" BASIS, 013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 014 * See the license for the specific language governing permissions and 015 * limitations under the license. 016 */ 017package org.apache.logging.log4j.core.config; 018 019import java.util.Comparator; 020import java.util.Objects; 021 022/** 023 * Comparator for classes annotated with {@link Order}. 024 * 025 * @since 2.1 026 */ 027public class OrderComparator implements Comparator<Class<?>> { 028 029 private static final Comparator<Class<?>> INSTANCE = new OrderComparator(); 030 031 /** 032 * Returns a singleton instance of this class. 033 * 034 * @return the singleton for this class. 035 */ 036 public static Comparator<Class<?>> getInstance() { 037 return INSTANCE; 038 } 039 040 @Override 041 public int compare(final Class<?> lhs, final Class<?> rhs) { 042 final Order lhsOrder = Objects.requireNonNull(lhs, "lhs").getAnnotation(Order.class); 043 final Order rhsOrder = Objects.requireNonNull(rhs, "rhs").getAnnotation(Order.class); 044 if (lhsOrder == null && rhsOrder == null) { 045 // both unannotated means equal priority 046 return 0; 047 } 048 // if only one class is @Order-annotated, then prefer that one 049 if (rhsOrder == null) { 050 return -1; 051 } 052 if (lhsOrder == null) { 053 return 1; 054 } 055 // larger value means lower priority 056 return Integer.signum(rhsOrder.value() - lhsOrder.value()); 057 } 058}