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.io.Serializable; 020import java.util.Comparator; 021import java.util.Objects; 022 023/** 024 * Comparator for classes annotated with {@link Order}. 025 * 026 * @since 2.1 027 */ 028public class OrderComparator implements Comparator<Class<?>>, Serializable { 029 030 private static final long serialVersionUID = 1L; 031 private static final Comparator<Class<?>> INSTANCE = new OrderComparator(); 032 033 /** 034 * Returns a singleton instance of this class. 035 * 036 * @return the singleton for this class. 037 */ 038 public static Comparator<Class<?>> getInstance() { 039 return INSTANCE; 040 } 041 042 @Override 043 public int compare(final Class<?> lhs, final Class<?> rhs) { 044 final Order lhsOrder = Objects.requireNonNull(lhs, "lhs").getAnnotation(Order.class); 045 final Order rhsOrder = Objects.requireNonNull(rhs, "rhs").getAnnotation(Order.class); 046 if (lhsOrder == null && rhsOrder == null) { 047 // both unannotated means equal priority 048 return 0; 049 } 050 // if only one class is @Order-annotated, then prefer that one 051 if (rhsOrder == null) { 052 return -1; 053 } 054 if (lhsOrder == null) { 055 return 1; 056 } 057 // larger value means higher priority 058 return Integer.signum(rhsOrder.value() - lhsOrder.value()); 059 } 060}