org.springframework.beans.factor

package org.springframework.beans.factory;

/**
 * A marker superinterface indicating that a bean is eligible to be notified by the
 * Spring container of a particular framework object through a callback-style method.
 * The actual method signature is determined by individual subinterfaces but should
 * typically consist of just one void-returning method that accepts a single argument.
 *
 * <p>Note that merely implementing {@link Aware} provides no default functionality.
 * Rather, processing must be done explicitly, for example in a
 * {@link org.springframework.beans.factory.config.BeanPostProcessor}.
 * Refer to {@link org.springframework.context.support.ApplicationContextAwareProcessor}
 * for an example of processing specific {@code *Aware} interface callbacks.
 *
 * @author Chris Beams
 * @author Juergen Hoeller
 * @since 3.1
 */
public interface Aware {

}

Aware 的含义

察觉、注意到、知道的。

Aware 接口文档

一个标记父接口，指示了一个 Bean 有资格被 Spring 容器通过一个回调风格的方法通知一个特定的框架对象。实际的方法签名是由各个子接口确定的，但通常应该仅包含一个接受单个参数、返回值为 void 的方法。

请注意，仅仅实现 Aware 接口不会提供默认功能。相反，处理必须明确地进行，例如在一个 org.springframework.beans.factory.config.BeanPostProcessor 中，请参阅 org.springframework.context.support.ApplicationContextAwareProcessor 中有关处理具体的 Aware 接口回调的示例。

例子

参考文档中提到的 ApplicationContextAwareProcessor，它实现了BeanPostProcessor接口。

@Override
@Nullable
public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
    if (!(bean instanceof EnvironmentAware || bean instanceof EmbeddedValueResolverAware ||
            bean instanceof ResourceLoaderAware || bean instanceof ApplicationEventPublisherAware ||
            bean instanceof MessageSourceAware || bean instanceof ApplicationContextAware)){
        return bean;
    }

    AccessControlContext acc = null;

    if (System.getSecurityManager() != null) {
        acc = this.applicationContext.getBeanFactory().getAccessControlContext();
    }

    if (acc != null) {
        AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
            invokeAwareInterfaces(bean);
            return null;
        }, acc);
    }
    else {
        invokeAwareInterfaces(bean);
    }

    return bean;
}

private void invokeAwareInterfaces(Object bean) {
    if (bean instanceof EnvironmentAware) {
        ((EnvironmentAware) bean).setEnvironment(this.applicationContext.getEnvironment());
    }
    if (bean instanceof EmbeddedValueResolverAware) {
        ((EmbeddedValueResolverAware) bean).setEmbeddedValueResolver(this.embeddedValueResolver);
    }
    if (bean instanceof ResourceLoaderAware) {
        ((ResourceLoaderAware) bean).setResourceLoader(this.applicationContext);
    }
    if (bean instanceof ApplicationEventPublisherAware) {
        ((ApplicationEventPublisherAware) bean).setApplicationEventPublisher(this.applicationContext);
    }
    if (bean instanceof MessageSourceAware) {
        ((MessageSourceAware) bean).setMessageSource(this.applicationContext);
    }
    if (bean instanceof ApplicationContextAware) {
        ((ApplicationContextAware) bean).setApplicationContext(this.applicationContext);
    }
}

当它调用 postProcessBeforeInitialization 方法时，会调用 invokeAwareInterfaces 方法。如果 Bean 实现了 Aware 的一个子接口，那么就会调用对应子接口中的方法。调用方法时，可能会传入一个参数，就是文档中提到的框架对象，如 applicationContext。