org.springframework.beans.factory.annotation.Autowired Maven / Gradle / Ivy
/*
* Copyright 2002-2018 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.beans.factory.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;
/**
* Marks a constructor, field, setter method or config method as to be autowired by
* Spring's dependency injection facilities. This is an alternative to the JSR-330
* {@link javax.inject.Inject} annotation, adding required-vs-optional semantics.
*
* Only one constructor (at max) of any given bean class may declare this annotation
* with the 'required' parameter set to {@code true}, indicating the constructor
* to autowire when used as a Spring bean. If multiple non-required constructors
* declare the annotation, they will be considered as candidates for autowiring.
* The constructor with the greatest number of dependencies that can be satisfied by
* matching beans in the Spring container will be chosen. If none of the candidates
* can be satisfied, then a primary/default constructor (if present) will be used.
* If a class only declares a single constructor to begin with, it will always be used,
* even if not annotated. An annotated constructor does not have to be public.
*
*
Fields are injected right after construction of a bean, before any config methods
* are invoked. Such a config field does not have to be public.
*
*
Config methods may have an arbitrary name and any number of arguments; each of
* those arguments will be autowired with a matching bean in the Spring container.
* Bean property setter methods are effectively just a special case of such a general
* config method. Such config methods do not have to be public.
*
*
In the case of a multi-arg constructor or method, the 'required' parameter is
* applicable to all arguments. Individual parameters may be declared as Java-8-style
* {@link java.util.Optional} or, as of Spring Framework 5.0, also as {@code @Nullable}
* or a not-null parameter type in Kotlin, overriding the base required semantics.
*
*
In case of a {@link java.util.Collection} or {@link java.util.Map} dependency type,
* the container autowires all beans matching the declared value type. For such purposes,
* the map keys must be declared as type String which will be resolved to the corresponding
* bean names. Such a container-provided collection will be ordered, taking into account
* {@link org.springframework.core.Ordered}/{@link org.springframework.core.annotation.Order}
* values of the target components, otherwise following their registration order in the
* container. Alternatively, a single matching target bean may also be a generally typed
* {@code Collection} or {@code Map} itself, getting injected as such.
*
*
Note that actual injection is performed through a
* {@link org.springframework.beans.factory.config.BeanPostProcessor
* BeanPostProcessor} which in turn means that you cannot
* use {@code @Autowired} to inject references into
* {@link org.springframework.beans.factory.config.BeanPostProcessor
* BeanPostProcessor} or
* {@link org.springframework.beans.factory.config.BeanFactoryPostProcessor BeanFactoryPostProcessor}
* types. Please consult the javadoc for the {@link AutowiredAnnotationBeanPostProcessor}
* class (which, by default, checks for the presence of this annotation).
*
* @author Juergen Hoeller
* @author Mark Fisher
* @since 2.5
* @see AutowiredAnnotationBeanPostProcessor
* @see Qualifier
* @see Value
*/
@Target({ElementType.CONSTRUCTOR, ElementType.METHOD, ElementType.PARAMETER, ElementType.FIELD, ElementType.ANNOTATION_TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface Autowired {
/**
* Declares whether the annotated dependency is required.
*
Defaults to {@code true}.
*/
boolean required() default true;
}