org.springframework.beans.factory.annotation.Value Maven / Gradle / Ivy
/*
* Copyright 2002-2019 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;
/**
* Annotation at the field or method/constructor parameter level
* that indicates a default value expression for the affected argument.
*
* Typically used for expression-driven dependency injection. Also supported
* for dynamic resolution of handler method parameters, e.g. in Spring MVC.
*
*
A common use case is to assign default field values using
* {@code #{systemProperties.myProp}} style expressions.
*
*
Note that actual processing of the {@code @Value} annotation is performed
* by a {@link org.springframework.beans.factory.config.BeanPostProcessor
* BeanPostProcessor} which in turn means that you cannot use
* {@code @Value} within
* {@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
* @since 3.0
* @see AutowiredAnnotationBeanPostProcessor
* @see Autowired
* @see org.springframework.beans.factory.config.BeanExpressionResolver
* @see org.springframework.beans.factory.support.AutowireCandidateResolver#getSuggestedValue
*/
@Target({ElementType.FIELD, ElementType.METHOD, ElementType.PARAMETER, ElementType.ANNOTATION_TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface Value {
/**
* The actual value expression: for example {@code #{systemProperties.myProp}}.
*/
String value();
}