spring Value 源码
spring Value 代码
文件路径：/spring-beans/src/main/java/org/springframework/beans/factory/annotation/Value.java
/*
* 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.
*/
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 used at the field or method/constructor parameter level
* that indicates a default value expression for the annotated element.
*
* <p>Typically used for expression-driven or property-driven dependency injection.
* Also supported for dynamic resolution of handler method arguments — for
* example, in Spring MVC.
*
* <p>A common use case is to inject values using
* <code>#{systemProperties.myProp}</code> style SpEL (Spring Expression Language)
* expressions. Alternatively, values may be injected using
* <code>${my.app.myProp}</code> style property placeholders.
*
* <p>Note that actual processing of the {@code @Value} annotation is performed
* by a {@link org.springframework.beans.factory.config.BeanPostProcessor
* BeanPostProcessor} which in turn means that you <em>cannot</em> use
* {@code @Value} within
* {@link org.springframework.beans.factory.config.BeanPostProcessor
* BeanPostProcessor} or
* {@link org.springframework.beans.factory.config.BeanFactoryPostProcessor BeanFactoryPostProcessor}
* types. Please consult the javadoc for the {@link AutowiredAnnotationBeanPostProcessor}
* class (which, by default, checks for the presence of this annotation).
*
* @author Juergen Hoeller
* @since 3.0
* @see AutowiredAnnotationBeanPostProcessor
* @see Autowired
* @see org.springframework.beans.factory.config.BeanExpressionResolver
* @see org.springframework.beans.factory.support.AutowireCandidateResolver#getSuggestedValue
*/
@Target({ElementType.FIELD, ElementType.METHOD, ElementType.PARAMETER, ElementType.ANNOTATION_TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface Value {
/**
* The actual value expression such as <code>#{systemProperties.myProp}</code>
* or property placeholder such as <code>${my.app.myProp}</code>.
*/
String value();
}
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