001/*
002 * Copyright 2012-2018 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 *      http://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.boot.autoconfigure.condition;
018
019import java.lang.annotation.Documented;
020import java.lang.annotation.ElementType;
021import java.lang.annotation.Retention;
022import java.lang.annotation.RetentionPolicy;
023import java.lang.annotation.Target;
024
025import org.springframework.beans.factory.BeanFactory;
026import org.springframework.context.annotation.Conditional;
027
028/**
029 * {@link Conditional} that only matches when a bean of the specified class is already
030 * contained in the {@link BeanFactory} and a single candidate can be determined.
031 * <p>
032 * The condition will also match if multiple matching bean instances are already contained
033 * in the {@link BeanFactory} but a primary candidate has been defined; essentially, the
034 * condition match if auto-wiring a bean with the defined type will succeed.
035 * <p>
036 * The condition can only match the bean definitions that have been processed by the
037 * application context so far and, as such, it is strongly recommended to use this
038 * condition on auto-configuration classes only. If a candidate bean may be created by
039 * another auto-configuration, make sure that the one using this condition runs after.
040 *
041 * @author Stephane Nicoll
042 * @since 1.3.0
043 */
044@Target({ ElementType.TYPE, ElementType.METHOD })
045@Retention(RetentionPolicy.RUNTIME)
046@Documented
047@Conditional(OnBeanCondition.class)
048public @interface ConditionalOnSingleCandidate {
049
050        /**
051         * The class type of bean that should be checked. The condition matches if a bean of
052         * the class specified is contained in the {@link BeanFactory} and a primary candidate
053         * exists in case of multiple instances.
054         * <p>
055         * This attribute may <strong>not</strong> be used in conjunction with
056         * {@link #type()}, but it may be used instead of {@link #type()}.
057         * @return the class type of the bean to check
058         */
059        Class<?> value() default Object.class;
060
061        /**
062         * The class type name of bean that should be checked. The condition matches if a bean
063         * of the class specified is contained in the {@link BeanFactory} and a primary
064         * candidate exists in case of multiple instances.
065         * <p>
066         * This attribute may <strong>not</strong> be used in conjunction with
067         * {@link #value()}, but it may be used instead of {@link #value()}.
068         * @return the class type name of the bean to check
069         */
070        String type() default "";
071
072        /**
073         * Strategy to decide if the application context hierarchy (parent contexts) should be
074         * considered.
075         * @return the search strategy
076         */
077        SearchStrategy search() default SearchStrategy.ALL;
078
079}