org.springframework.context.annotation.Primary Maven / Gradle / Ivy
/*
* Copyright 2002-2011 the original author or authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.springframework.context.annotation;
import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Inherited;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
/**
* Indicates that a bean should be given preference when multiple candidates
* are qualified to autowire a single-valued dependency. If exactly one 'primary'
* bean exists among the candidates, it will be the autowired value. This annotation
* is semantically equivalent to the {@code } element's {@code primary} attribute
* in Spring XML.
*
* May be used on any class directly or indirectly annotated with @{@link
* org.springframework.stereotype.Component Component} or on methods annotated
* with @{@link Bean}.
*
*
Example
*
* @Component
* public class FooService {
* private FooRepository fooRepository;
*
* @Autowired
* public FooService(FooRepository fooRepository) {
* this.fooRepository = fooRepository;
* }
* }
*
* @Component
* public class JdbcFooRepository {
* public JdbcFooService(DataSource dataSource) {
* // ...
* }
* }
*
* @Primary
* @Component
* public class HibernateFooRepository {
* public HibernateFooService(SessionFactory sessionFactory) {
* // ...
* }
* }
*
*
* Because {@code HibernateFooRepository} is marked with {@code @Primary}, it will
* be injected preferentially over the jdbc-based variant assuming both are present as
* beans within the same Spring application context, which is often the case when
* component-scanning is applied liberally.
*
*
Note that using {@code @Primary} at the class level has no effect unless
* component-scanning is being used. If a {@code @Primary}-annotated class is declared via
* XML, {@code @Primary} annotation metadata is ignored, and
* {@code