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.io.Serializable; 20 import java.util.Comparator; 21 import java.util.Objects; 22 23 /** 24 * Comparator for classes annotated with {@link Order}. 25 * 26 * @since 2.1 27 */ 28 public class OrderComparator implements Comparator<Class<?>>, Serializable { 29 30 private static final long serialVersionUID = 1L; 31 private static final Comparator<Class<?>> INSTANCE = new OrderComparator(); 32 33 /** 34 * Returns a singleton instance of this class. 35 * 36 * @return the singleton for this class. 37 */ 38 public static Comparator<Class<?>> getInstance() { 39 return INSTANCE; 40 } 41 42 @Override 43 public int compare(final Class<?> lhs, final Class<?> rhs) { 44 final Order lhsOrder = Objects.requireNonNull(lhs, "lhs").getAnnotation(Order.class); 45 final Order rhsOrder = Objects.requireNonNull(rhs, "rhs").getAnnotation(Order.class); 46 if (lhsOrder == null && rhsOrder == null) { 47 // both unannotated means equal priority 48 return 0; 49 } 50 // if only one class is @Order-annotated, then prefer that one 51 if (rhsOrder == null) { 52 return -1; 53 } 54 if (lhsOrder == null) { 55 return 1; 56 } 57 // larger value means lower priority 58 return Integer.signum(rhsOrder.value() - lhsOrder.value()); 59 } 60 }