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
21 import org.apache.logging.log4j.core.util.Assert;
22
23 /**
24 * Comparator for classes annotated with {@link Order}.
25 *
26 * @since 2.1
27 */
28 public class OrderComparator implements Comparator<Class<?>> {
29
30 private static final Comparator<Class<?>> INSTANCE = new OrderComparator();
31
32 /**
33 * Returns a singleton instance of this class.
34 *
35 * @return the singleton for this class.
36 */
37 public static Comparator<Class<?>> getInstance() {
38 return INSTANCE;
39 }
40
41 @Override
42 public int compare(final Class<?> lhs, final Class<?> rhs) {
43 final Order lhsOrder = Assert.requireNonNull(lhs, "lhs").getAnnotation(Order.class);
44 final Order rhsOrder = Assert.requireNonNull(rhs, "rhs").getAnnotation(Order.class);
45 if (lhsOrder == null && rhsOrder == null) {
46 // both unannotated means equal priority
47 return 0;
48 }
49 // if only one class is @Order-annotated, then prefer that one
50 if (rhsOrder == null) {
51 return -1;
52 }
53 if (lhsOrder == null) {
54 return 1;
55 }
56 // larger value means lower priority
57 return Integer.signum(rhsOrder.value() - lhsOrder.value());
58 }
59 }