前言
咱們在編寫代碼的時候，有的時候想要使用Spring的底層組件，相似於 ApplicationContext, BeanFactory等等java
那咱們實現Spring提供的鉤子方法xxxAware。在建立對象的時候，會調用接口規定的方法注入相關的組件。spring
Aware接口
1 /** 2 * A marker superinterface indicating that a bean is eligible to be notified by the 3 * Spring container of a particular framework object through a callback-style method. 4 * The actual method signature is determined by individual subinterfaces but should 5 * typically consist of just one void-returning method that accepts a single argument. 6 * 7 * <p>Note that merely implementing {@link Aware} provides no default functionality. 8 * Rather, processing must be done explicitly, for example in a 9 * {@link org.springframework.beans.factory.config.BeanPostProcessor}. 10 * Refer to {@link org.springframework.context.support.ApplicationContextAwareProcessor} 11 * for an example of processing specific {@code *Aware} interface callbacks. 12 * 13 * @author Chris Beams 14 * @author Juergen Hoeller 15 * @since 3.1 16 */ 17 public interface Aware {}
一個標記的超級接口，代表這個bean會被spring容器注意到，經過一個回調的風格。這個我也稱之爲鉤子方法。app
咱們能夠看到以下圖片，實現了Aware的接口的接口特別多，他們都是Spring自帶的組件，咱們經過Aware能夠很方便的使用他們。ide
在此列舉幾個比較重要的接口，都是我常常用到的。post
| Aware子接口 | 描述 |
|---|---|
| BeanNameAware | 獲取容器中 Bean 的名稱 |
| BeanFactoryAware | 獲取當前 BeanFactory ，這樣能夠調用容器的服務 |
| ApplicationContextAware | 注入IOC容器的，能夠使用容器絕大部分功能 |
| MessageSourceAware | 獲取 Message Source 相關文本信息 |
| EmbeddedValueResolverAware | 值解析器，好比{} #{}等等 |
| EnvironmentAware | 環境解析器，能夠拿properties的時候挺好用的 |
ApplicationContextAware接口
1 public interface ApplicationContextAware extends Aware { 2 3 /** 4 * Set the ApplicationContext that this object runs in. 5 * Normally this call will be used to initialize the object. 6 * <p>Invoked after population of normal bean properties but before an init callback such 7 * as {@link org.springframework.beans.factory.InitializingBean#afterPropertiesSet()} 8 * or a custom init-method. Invoked after {@link ResourceLoaderAware#setResourceLoader}, 9 * {@link ApplicationEventPublisherAware#setApplicationEventPublisher} and 10 * {@link MessageSourceAware}, if applicable. 11 * @param applicationContext the ApplicationContext object to be used by this object 12 * @throws ApplicationContextException in case of context initialization errors 13 * @throws BeansException if thrown by application context methods 14 * @see org.springframework.beans.factory.BeanInitializationException 15 */ 16 void setApplicationContext(ApplicationContext applicationContext) throws BeansException; 17 18 }
這個能夠獲取Spring的IOC容器。拿到這個IOC容器，你能夠擁有Spring的絕大多數功能。this
咱們以ApplicationContextAware爲例。直接繼承XxxAware接口，就能夠拿到他的相應字段了。spa
1 @Component 2 @Slf4j 3 public class Person implements ApplicationContextAware, BeanFactoryAware, 4 BeanNameAware, EnvironmentAware, EmbeddedValueResolverAware { 5 6 @Override 7 public void setApplicationContext(ApplicationContext applicationContext) throws BeansException { 8 log.info("applicationContext = {}", applicationContext.getBean("person")); 9 } 10 11 @Override 12 public void setBeanFactory(BeanFactory beanFactory) throws BeansException { 13 log.info("beanFactory = {}", beanFactory.containsBean("person")); 14 } 15 16 @Override 17 public void setBeanName(String name) { 18 log.info("name = {}", name); 19 } 20 21 @Override 22 public void setEmbeddedValueResolver(StringValueResolver resolver) { 23 // 字符解析器 24 log.info("val = {}", resolver.resolveStringValue("#{5 * 10}")); 25 } 26 27 @Override 28 public void setEnvironment(Environment environment) { 29 // 這個能夠獲取環境變量的值 30 log.info("app = {}", environment.getProperty("app.secret")); 31 } 32 }
結果：code
1 2020-04-04 21:35:39.474 [main] [] INFO - [com.gdufe.osc.controller.Person java:37] [name = person] 2 2020-04-04 21:35:39.475 [main] [] INFO - [com.gdufe.osc.controller.Person java:32] [beanFactory = true] 3 2020-04-04 21:35:39.475 [main] [] INFO - [com.gdufe.osc.controller.Person java:48] [app = wenbochang888] 4 2020-04-04 21:35:39.491 [main] [] INFO - [com.gdufe.osc.controller.Person java:42] [val = 50] 5 2020-04-04 21:35:39.493 [main] [] INFO - [com.gdufe.osc.controller.Person java:27] [applicationContext = com.gdufe.osc.controller.Person@24386839]
Aware接口底層實現原理
咱們看下以下的代碼orm
1 class ApplicationContextAwareProcessor implements BeanPostProcessor { 2 3 @Override 4 @Nullable 5 public Object postProcessBeforeInitialization(final Object bean, String beanName) throws BeansException { 6 7 ..... 8 invokeAwareInterfaces(bean); 9 ..... 10 11 return bean; 12 } 13 14 private void invokeAwareInterfaces(Object bean) { 15 if (bean instanceof Aware) { 16 if (bean instanceof EnvironmentAware) { 17 ((EnvironmentAware) bean).setEnvironment(this.applicationContext.getEnvironment()); 18 } 19 if (bean instanceof EmbeddedValueResolverAware) { 20 ((EmbeddedValueResolverAware) bean).setEmbeddedValueResolver(this.embeddedValueResolver); 21 } 22 if (bean instanceof ResourceLoaderAware) { 23 ((ResourceLoaderAware) bean).setResourceLoader(this.applicationContext); 24 } 25 if (bean instanceof ApplicationEventPublisherAware) { 26 ((ApplicationEventPublisherAware) bean).setApplicationEventPublisher(this.applicationContext); 27 } 28 if (bean instanceof MessageSourceAware) { 29 ((MessageSourceAware) bean).setMessageSource(this.applicationContext); 30 } 31 if (bean instanceof ApplicationContextAware) { 32 ((ApplicationContextAware) bean).setApplicationContext(this.applicationContext); 33 } 34 } 35 } 36 }
這裏我稍微解釋一下 BeanPostProcessor 方法。在初始化bean以前，以及以後，能夠執行相應的方法。相似有點AOP的功能。對象
那麼ApplicationContextAwareProcessor 就很好理解了。
在一個bean實例初始化以前調用postProcessBeforeInitialization方法。而後判斷該bean有沒有實現相應的aware接口，將對於的aware set進去便可，很是的方便。