001/*
002 * Copyright 2002-2019 the original author or authors.
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 *      https://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016
017package org.springframework.core.annotation;
018
019import java.lang.annotation.Annotation;
020import java.util.function.Predicate;
021
022/**
023 * {@link MergedAnnotationSelector} implementations that provide various options
024 * for {@link MergedAnnotation} instances.
025 *
026 * @author Phillip Webb
027 * @since 5.2
028 * @see MergedAnnotations#get(Class, Predicate, MergedAnnotationSelector)
029 * @see MergedAnnotations#get(String, Predicate, MergedAnnotationSelector)
030 */
031public abstract class MergedAnnotationSelectors {
032
033        private static final MergedAnnotationSelector<?> NEAREST = new Nearest();
034
035        private static final MergedAnnotationSelector<?> FIRST_DIRECTLY_DECLARED = new FirstDirectlyDeclared();
036
037
038        private MergedAnnotationSelectors() {
039        }
040
041
042        /**
043         * Select the nearest annotation, i.e. the one with the lowest distance.
044         * @return a selector that picks the annotation with the lowest distance
045         */
046        @SuppressWarnings("unchecked")
047        public static <A extends Annotation> MergedAnnotationSelector<A> nearest() {
048                return (MergedAnnotationSelector<A>) NEAREST;
049        }
050
051        /**
052         * Select the first directly declared annotation when possible. If no direct
053         * annotations are declared then the nearest annotation is selected.
054         * @return a selector that picks the first directly declared annotation whenever possible
055         */
056        @SuppressWarnings("unchecked")
057        public static <A extends Annotation> MergedAnnotationSelector<A> firstDirectlyDeclared() {
058                return (MergedAnnotationSelector<A>) FIRST_DIRECTLY_DECLARED;
059        }
060
061
062        /**
063         * {@link MergedAnnotationSelector} to select the nearest annotation.
064         */
065        private static class Nearest implements MergedAnnotationSelector<Annotation> {
066
067                @Override
068                public boolean isBestCandidate(MergedAnnotation<Annotation> annotation) {
069                        return annotation.getDistance() == 0;
070                }
071
072                @Override
073                public MergedAnnotation<Annotation> select(
074                                MergedAnnotation<Annotation> existing, MergedAnnotation<Annotation> candidate) {
075
076                        if (candidate.getDistance() < existing.getDistance()) {
077                                return candidate;
078                        }
079                        return existing;
080                }
081
082        }
083
084
085        /**
086         * {@link MergedAnnotationSelector} to select the first directly declared
087         * annotation.
088         */
089        private static class FirstDirectlyDeclared implements MergedAnnotationSelector<Annotation> {
090
091                @Override
092                public boolean isBestCandidate(MergedAnnotation<Annotation> annotation) {
093                        return annotation.getDistance() == 0;
094                }
095
096                @Override
097                public MergedAnnotation<Annotation> select(
098                                MergedAnnotation<Annotation> existing, MergedAnnotation<Annotation> candidate) {
099
100                        if (existing.getDistance() > 0 && candidate.getDistance() == 0) {
101                                return candidate;
102                        }
103                        return existing;
104                }
105
106        }
107
108}