001/* 002 * Copyright 2002-2016 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 * 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.context.annotation; 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; 024 025/** 026 * Indicates that a bean should be given preference when multiple candidates 027 * are qualified to autowire a single-valued dependency. If exactly one 028 * 'primary' bean exists among the candidates, it will be the autowired value. 029 * 030 * <p>This annotation is semantically equivalent to the {@code <bean>} element's 031 * {@code primary} attribute in Spring XML. 032 * 033 * <p>May be used on any class directly or indirectly annotated with 034 * {@code @Component} or on methods annotated with @{@link Bean}. 035 * 036 * <h2>Example</h2> 037 * <pre class="code"> 038 * @Component 039 * public class FooService { 040 * 041 * private FooRepository fooRepository; 042 * 043 * @Autowired 044 * public FooService(FooRepository fooRepository) { 045 * this.fooRepository = fooRepository; 046 * } 047 * } 048 * 049 * @Component 050 * public class JdbcFooRepository extends FooRepository { 051 * 052 * public JdbcFooRepository(DataSource dataSource) { 053 * // ... 054 * } 055 * } 056 * 057 * @Primary 058 * @Component 059 * public class HibernateFooRepository extends FooRepository { 060 * 061 * public HibernateFooRepository(SessionFactory sessionFactory) { 062 * // ... 063 * } 064 * } 065 * </pre> 066 * 067 * <p>Because {@code HibernateFooRepository} is marked with {@code @Primary}, 068 * it will be injected preferentially over the jdbc-based variant assuming both 069 * are present as beans within the same Spring application context, which is 070 * often the case when component-scanning is applied liberally. 071 * 072 * <p>Note that using {@code @Primary} at the class level has no effect unless 073 * component-scanning is being used. If a {@code @Primary}-annotated class is 074 * declared via XML, {@code @Primary} annotation metadata is ignored, and 075 * {@code <bean primary="true|false"/>} is respected instead. 076 * 077 * @author Chris Beams 078 * @author Juergen Hoeller 079 * @since 3.0 080 * @see Lazy 081 * @see Bean 082 * @see ComponentScan 083 * @see org.springframework.stereotype.Component 084 */ 085@Target({ElementType.TYPE, ElementType.METHOD}) 086@Retention(RetentionPolicy.RUNTIME) 087@Documented 088public @interface Primary { 089 090}