/*
* Copyright 2002-2020 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.
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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;
An annotation that indicates 'lookup' methods, to be overridden by the container to redirect them back to the BeanFactory for a getBean call. This is essentially an annotation-based version of the XML lookup-method attribute, resulting in the same runtime arrangement. The resolution of the target bean can either be based on the return type (getBean(Class)) or on a suggested bean name (getBean(String)), in both cases passing the method's arguments to the getBean call for applying them as target factory method arguments or constructor arguments.
Such lookup methods can have default (stub) implementations that will simply
get replaced by the container, or they can be declared as abstract - for the
container to fill them in at runtime. In both cases, the container will generate
runtime subclasses of the method's containing class via CGLIB, which is why such
lookup methods can only work on beans that the container instantiates through
regular constructors: i.e. lookup methods cannot get replaced on beans returned
from factory methods where we cannot dynamically provide a subclass for them.
Recommendations for typical Spring configuration scenarios: When a concrete class may be needed in certain scenarios, consider providing stub implementations of your lookup methods. And please remember that lookup methods won't work on beans returned from @Bean methods in configuration classes; you'll have to resort to @Inject Provider<TargetBean> or the like instead.
Author: Juergen Hoeller See Also: Since: 4.1
/**
* An annotation that indicates 'lookup' methods, to be overridden by the container
* to redirect them back to the {@link org.springframework.beans.factory.BeanFactory}
* for a {@code getBean} call. This is essentially an annotation-based version of the
* XML {@code lookup-method} attribute, resulting in the same runtime arrangement.
*
* <p>The resolution of the target bean can either be based on the return type
* ({@code getBean(Class)}) or on a suggested bean name ({@code getBean(String)}),
* in both cases passing the method's arguments to the {@code getBean} call
* for applying them as target factory method arguments or constructor arguments.
*
* <p>Such lookup methods can have default (stub) implementations that will simply
* get replaced by the container, or they can be declared as abstract - for the
* container to fill them in at runtime. In both cases, the container will generate
* runtime subclasses of the method's containing class via CGLIB, which is why such
* lookup methods can only work on beans that the container instantiates through
* regular constructors: i.e. lookup methods cannot get replaced on beans returned
* from factory methods where we cannot dynamically provide a subclass for them.
*
* <p><b>Recommendations for typical Spring configuration scenarios:</b>
* When a concrete class may be needed in certain scenarios, consider providing stub
* implementations of your lookup methods. And please remember that lookup methods
* won't work on beans returned from {@code @Bean} methods in configuration classes;
* you'll have to resort to {@code @Inject Provider<TargetBean>} or the like instead.
*
* @author Juergen Hoeller
* @since 4.1
* @see org.springframework.beans.factory.BeanFactory#getBean(Class, Object...)
* @see org.springframework.beans.factory.BeanFactory#getBean(String, Object...)
*/
@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface Lookup {
This annotation attribute may suggest a target bean name to look up.
If not specified, the target bean will be resolved based on the
annotated method's return type declaration.
/**
* This annotation attribute may suggest a target bean name to look up.
* If not specified, the target bean will be resolved based on the
* annotated method's return type declaration.
*/
String value() default "";
}