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 higher priority
58 return Integer.signum(rhsOrder.value() - lhsOrder.value());
59 }
60 }