1 /* 2 * Licensed to the Apache Software Foundation (ASF) under one or more 3 * contributor license agreements. See the NOTICE file distributed with 4 * this work for additional information regarding copyright ownership. 5 * The ASF licenses this file to You under the Apache license, Version 2.0 6 * (the "License"); you may not use this file except in compliance with 7 * the License. You may obtain a copy of the License at 8 * 9 * http://www.apache.org/licenses/LICENSE-2.0 10 * 11 * Unless required by applicable law or agreed to in writing, software 12 * distributed under the License is distributed on an "AS IS" BASIS, 13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 14 * See the license for the specific language governing permissions and 15 * limitations under the license. 16 */ 17 package org.apache.logging.log4j.core.config; 18 19 import java.util.Comparator; 20 import java.util.Objects; 21 22 /** 23 * Comparator for classes annotated with {@link Order}. 24 * 25 * @since 2.1 26 */ 27 public class OrderComparator implements Comparator<Class<?>> { 28 29 private static final Comparator<Class<?>> INSTANCE = new OrderComparator(); 30 31 /** 32 * Returns a singleton instance of this class. 33 * 34 * @return the singleton for this class. 35 */ 36 public static Comparator<Class<?>> getInstance() { 37 return INSTANCE; 38 } 39 40 @Override 41 public int compare(final Class<?> lhs, final Class<?> rhs) { 42 final Order lhsOrder = Objects.requireNonNull(lhs, "lhs").getAnnotation(Order.class); 43 final Order rhsOrder = Objects.requireNonNull(rhs, "rhs").getAnnotation(Order.class); 44 if (lhsOrder == null && rhsOrder == null) { 45 // both unannotated means equal priority 46 return 0; 47 } 48 // if only one class is @Order-annotated, then prefer that one 49 if (rhsOrder == null) { 50 return -1; 51 } 52 if (lhsOrder == null) { 53 return 1; 54 } 55 // larger value means lower priority 56 return Integer.signum(rhsOrder.value() - lhsOrder.value()); 57 } 58 }