Spring Aware 接口

Spring Aware 接口

Spring框架中的Aware接口是一个特殊的标记接口，用表示该 Bean 可以接受 Spring容器特定的对象。

in short 实现这些内置子接口的Bean, Spring 在实例化时过程中会调用其方法, 将Spring框架特定的对象注入

org.springframework.beans.factory.Aware

/**  * 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.  *  * Spring框架中的`Aware`接口是一个特殊的标记接口，用表示该 Bean 可以接受 Spring容器特定的对象。  * 注意 `Aware` 接口仅作为一个标记, 实际的注入对象, 由各个子接口方法的签名确定  *  * <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 的子接口

相关注入的源码

ApplicationContextAwareProcessor 是一个 BPP 它本身会在容器启动准备BeanFactory 的过程中org.springframework.context.support.AbstractApplicationContext#prepareBeanFactory 添加到 beanFactory 中

/**  * Configure the factory's standard context characteristics,  * such as the context's ClassLoader and post-processors.  * @param beanFactory the BeanFactory to configure  */ protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) { 	// Tell the internal bean factory to use the context's class loader etc. 	/** 	 * 为 beanFactory 设置 bean 的类加载器 	 */ 	beanFactory.setBeanClassLoader(getClassLoader()); 	/** 	 * 为 beanFactory 设置 bean 的表达式(Spring EL)解析器 	 */ 	beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver(beanFactory.getBeanClassLoader()));  	/** 	 *  为 beanFactory 设置 PropertyEditorRegistrar 	 */ 	beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, getEnvironment()));  	/** 	 * <!>添加一个 BeanPostProcessor 回调, 作用是如果Bean实现这些接口: 	 * (bean instanceof EnvironmentAware || bean instanceof EmbeddedValueResolverAware || 	 * 				bean instanceof ResourceLoaderAware || bean instanceof ApplicationEventPublisherAware || 	 * 				bean instanceof MessageSourceAware || bean instanceof ApplicationContextAware || 	 * 				bean instanceof ApplicationStartupAware) 	 *  它负责调用其对应 Aware 的方法, 给Bean 注入对象 	 * 	 * in short 就是给 bean 设置 上下文, 内置的对象; 注意是 (postProcessBeforeInitialization) 	 */ 	// Configure the bean factory with context callbacks. 	beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this)); ......  

org.springframework.context.support.ApplicationContextAwareProcessor 的源码

package org.springframework.context.support;  import org.springframework.beans.BeansException; import org.springframework.beans.factory.Aware; import org.springframework.beans.factory.config.BeanPostProcessor; import org.springframework.beans.factory.config.EmbeddedValueResolver; import org.springframework.context.ApplicationContextAware; import org.springframework.context.ApplicationEventPublisherAware; import org.springframework.context.ApplicationStartupAware; import org.springframework.context.ConfigurableApplicationContext; import org.springframework.context.EmbeddedValueResolverAware; import org.springframework.context.EnvironmentAware; import org.springframework.context.MessageSourceAware; import org.springframework.context.ResourceLoaderAware; import org.springframework.lang.Nullable; import org.springframework.util.StringValueResolver;  /**  * {@link BeanPostProcessor} implementation that supplies the {@code ApplicationContext},  * {@link org.springframework.core.env.Environment Environment}, or  * {@link StringValueResolver} for the {@code ApplicationContext} to beans that  * implement the {@link EnvironmentAware}, {@link EmbeddedValueResolverAware},  * {@link ResourceLoaderAware}, {@link ApplicationEventPublisherAware},  * {@link MessageSourceAware}, and/or {@link ApplicationContextAware} interfaces.  *  * <p>Implemented interfaces are satisfied in the order in which they are  * mentioned above.  *  * <p>Application contexts will automatically register this with their  * underlying bean factory. Applications do not use this directly.  *  * @author Juergen Hoeller  * @author Costin Leau  * @author Chris Beams  * @author Sam Brannen  * @since 10.10.2003  * @see org.springframework.context.EnvironmentAware  * @see org.springframework.context.EmbeddedValueResolverAware  * @see org.springframework.context.ResourceLoaderAware  * @see org.springframework.context.ApplicationEventPublisherAware  * @see org.springframework.context.MessageSourceAware  * @see org.springframework.context.ApplicationContextAware  * @see org.springframework.context.support.AbstractApplicationContext#refresh()  */ class ApplicationContextAwareProcessor implements BeanPostProcessor {  	private final ConfigurableApplicationContext applicationContext;  	private final StringValueResolver embeddedValueResolver;   	/** 	 * Create a new ApplicationContextAwareProcessor for the given context. 	 */ 	public ApplicationContextAwareProcessor(ConfigurableApplicationContext applicationContext) { 		this.applicationContext = applicationContext; 		this.embeddedValueResolver = new EmbeddedValueResolver(applicationContext.getBeanFactory()); 	}   	@Override 	@Nullable 	public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException { 		/** 		 * 这里只处理以下的7种对象的 Aware注入, 若不是则返回不处理 		 */ 		if (!(bean instanceof EnvironmentAware || bean instanceof EmbeddedValueResolverAware || 				bean instanceof ResourceLoaderAware || bean instanceof ApplicationEventPublisherAware || 				bean instanceof MessageSourceAware || bean instanceof ApplicationContextAware || 				bean instanceof ApplicationStartupAware)) { 			return bean; 		} 		// 		invokeAwareInterfaces(bean); 		return bean; 	}  	private void invokeAwareInterfaces(Object bean) { 		if (bean instanceof Aware) { 			if (bean instanceof EnvironmentAware environmentAware) { 				environmentAware.setEnvironment(this.applicationContext.getEnvironment()); 			} 			if (bean instanceof EmbeddedValueResolverAware embeddedValueResolverAware) { 				embeddedValueResolverAware.setEmbeddedValueResolver(this.embeddedValueResolver); 			} 			if (bean instanceof ResourceLoaderAware resourceLoaderAware) { 				resourceLoaderAware.setResourceLoader(this.applicationContext); 			} 			if (bean instanceof ApplicationEventPublisherAware applicationEventPublisherAware) { 				applicationEventPublisherAware.setApplicationEventPublisher(this.applicationContext); 			} 			if (bean instanceof MessageSourceAware messageSourceAware) { 				messageSourceAware.setMessageSource(this.applicationContext); 			} 			if (bean instanceof ApplicationStartupAware applicationStartupAware) { 				applicationStartupAware.setApplicationStartup(this.applicationContext.getApplicationStartup()); 			} 			if (bean instanceof ApplicationContextAware applicationContextAware) { 				applicationContextAware.setApplicationContext(this.applicationContext); 			} 		} 	}  }  

1. Environment 对象。Environment对象代表了当前应用运行的环境，它可以用来获取配置属性（如系统属性、环境变量、配置文件中的属性等）。通过Environment，可以方便地访问各种配置信息，并且支持 profiles 和 properties 的解析。
2. EmbeddedValueResolver对象。这个对象用于解析字符串中的占位符（如${...}）和SpEL表达式（如#{...}）。它通常用于注解驱动或XML配置中，用于解析嵌入在字符串中的值。
3. ResourceLoader 是用于加载资源（如类路径下的文件、文件系统中的文件、URL资源等）的策略接口。ApplicationContext 本身就是一个ResourceLoader，所以这里将applicationContext作为ResourceLoader注入。
4. ApplicationEventPublisher 对象。这个对象用于发布应用事件。Spring的事件机制是基于观察者模式的，通过ApplicationEventPublisher发布事件，然后由相应的ApplicationListener监听器处理。这里同样使用 applicationContext 作为事件发布器，因为ApplicationContext实现了ApplicationEventPublisher接口。
5. MessageSource 是用于国际化（i18n）的消息接口，它可以解析消息代码并返回对应的消息字符串。通过MessageSource，可以实现多语言支持。
6. ApplicationStartup 是Spring 5.3引入的，用于跟踪应用启动过程中的各个步骤，从而可以收集启动性能指标。它允许开发者监控应用启动的各个阶段。
7. ApplicationContext 是Spring容器的核心接口，它提供了配置应用上下文的功能，包括获取bean、发布事件、访问环境、国际化等功能。通过实现这个接口，bean可以直接访问容器，但通常不推荐这样做，因为这样会导致代码与Spring框架耦合。