001/*
002 * Copyright 2012-2016 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.ApplicationContext;
027import org.springframework.context.annotation.Conditional;
028
029/**
030 * {@link Conditional} that only matches when the specified bean class is already
031 * contained in the {@link BeanFactory} and a single candidate can be determined.
032 * <p>
033 * The condition will also match if multiple matching bean instances are already contained
034 * in the {@link BeanFactory} but a primary candidate has been defined; essentially, the
035 * condition match if auto-wiring a bean with the defined type will succeed.
036 * <p>
037 * The condition can only match the bean definitions that have been processed by the
038 * application context so far and, as such, it is strongly recommended to use this
039 * condition on auto-configuration classes only. If a candidate bean may be created by
040 * another auto-configuration, make sure that the one using this condition runs after.
041 *
042 * @author Stephane Nicoll
043 * @since 1.3.0
044 */
045@Target({ ElementType.TYPE, ElementType.METHOD })
046@Retention(RetentionPolicy.RUNTIME)
047@Documented
048@Conditional(OnBeanCondition.class)
049public @interface ConditionalOnSingleCandidate {
050
051        /**
052         * The class type of bean that should be checked. The condition match if the class
053         * specified is contained in the {@link ApplicationContext} and a primary candidate
054         * exists in case of multiple instances.
055         * <p>
056         * This attribute may <strong>not</strong> be used in conjunction with {@link #type()}
057         * , but it may be used instead of {@link #type()}.
058         * @return the class type of the bean to check
059         */
060        Class<?> value() default Object.class;
061
062        /**
063         * The class type name of bean that should be checked. The condition matches if the
064         * class specified is contained in the {@link ApplicationContext} and a primary
065         * candidate exists in case of multiple instances.
066         * <p>
067         * This attribute may <strong>not</strong> be used in conjunction with
068         * {@link #value()}, but it may be used instead of {@link #value()}.
069         * @return the class type name of the bean to check
070         */
071        String type() default "";
072
073        /**
074         * Strategy to decide if the application context hierarchy (parent contexts) should be
075         * considered.
076         * @return the search strategy
077         */
078        SearchStrategy search() default SearchStrategy.ALL;
079
080}