spring Primary 源码
spring Primary 代码
文件路径：/spring-context/src/main/java/org/springframework/context/annotation/Primary.java
/*
* Copyright 2002-2016 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
*
* https://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.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.
*
* <p>This annotation is semantically equivalent to the {@code <bean>} element's
* {@code primary} attribute in Spring XML.
*
* <p>May be used on any class directly or indirectly annotated with
* {@code @Component} or on methods annotated with @{@link Bean}.
*
* <h2>Example</h2>
* <pre class="code">
* @Component
* public class FooService {
*
* private FooRepository fooRepository;
*
* @Autowired
* public FooService(FooRepository fooRepository) {
* this.fooRepository = fooRepository;
* }
* }
*
* @Component
* public class JdbcFooRepository extends FooRepository {
*
* public JdbcFooRepository(DataSource dataSource) {
* // ...
* }
* }
*
* @Primary
* @Component
* public class HibernateFooRepository extends FooRepository {
*
* public HibernateFooRepository(SessionFactory sessionFactory) {
* // ...
* }
* }
* </pre>
*
* <p>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.
*
* <p>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 <bean primary="true|false"/>} is respected instead.
*
* @author Chris Beams
* @author Juergen Hoeller
* @since 3.0
* @see Lazy
* @see Bean
* @see ComponentScan
* @see org.springframework.stereotype.Component
*/
@Target({ElementType.TYPE, ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface Primary {
}
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