Spring之ApplicationContextAware使用详解

Spring之ApplicationContextAware使用详解

Spring定义的类实现ApplicationContextAware接口会自动的将应用程序上下文加入，首先我们看下具体的实现示例；

示例代码

• package com.yaomy.security.oauth2.filter;
  
  import org.springframework.beans.BeansException;
  import org.springframework.context.ApplicationContext;
  import org.springframework.context.ApplicationContextAware;
  import org.springframework.stereotype.Component;
  
  /**
   * @Description: Description
   * @ProjectName: spring-parent
   * @Package: com.yaomy.security.oauth2.filter.BeanUtils
   * @Date: 2019/8/1 10:58
   * @Version: 1.0
   */
  @Component
  public class BeanUtils implements ApplicationContextAware {
      private ApplicationContext applicationContext;
      @Override
      public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
          this.applicationContext = applicationContext;
      }
  }
  

ApplicationContextAware的使用方式很简单，只要实现接口重写方法就可以，下面我们看下应用程序是如何初始化的

• AbstractApplicationContext类是Spring容器应用上下文的一个抽象父类，我们看下里面的prepareBeanFactory方法

•   protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) {
          beanFactory.setBeanClassLoader(this.getClassLoader());
          beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver(beanFactory.getBeanClassLoader()));
          beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, this.getEnvironment()));
          //添加ApplicationContextAware的处理器
          beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));
          beanFactory.ignoreDependencyInterface(EnvironmentAware.class);
          beanFactory.ignoreDependencyInterface(EmbeddedValueResolverAware.class);
          beanFactory.ignoreDependencyInterface(ResourceLoaderAware.class);
          beanFactory.ignoreDependencyInterface(ApplicationEventPublisherAware.class);
          beanFactory.ignoreDependencyInterface(MessageSourceAware.class);
          beanFactory.ignoreDependencyInterface(ApplicationContextAware.class);
          beanFactory.registerResolvableDependency(BeanFactory.class, beanFactory);
          beanFactory.registerResolvableDependency(ResourceLoader.class, this);
          beanFactory.registerResolvableDependency(ApplicationEventPublisher.class, this);
          beanFactory.registerResolvableDependency(ApplicationContext.class, this);
          beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(this));
          if (beanFactory.containsBean("loadTimeWeaver")) {
              beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
              beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
          }
  
          if (!beanFactory.containsLocalBean("environment")) {
              beanFactory.registerSingleton("environment", this.getEnvironment());
          }
  
          if (!beanFactory.containsLocalBean("systemProperties")) {
              beanFactory.registerSingleton("systemProperties", this.getEnvironment().getSystemProperties());
          }
  
          if (!beanFactory.containsLocalBean("systemEnvironment")) {
              beanFactory.registerSingleton("systemEnvironment", this.getEnvironment().getSystemEnvironment());
          }
  
      }
  

进入ApplicationContextAwareProcessor处理器类查看代码

•     @Nullable
      public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
          AccessControlContext acc = null;
          if (System.getSecurityManager() != null && (bean instanceof EnvironmentAware || bean instanceof EmbeddedValueResolverAware || bean instanceof ResourceLoaderAware || bean instanceof ApplicationEventPublisherAware || bean instanceof MessageSourceAware || bean instanceof ApplicationContextAware)) {
              acc = this.applicationContext.getBeanFactory().getAccessControlContext();
          }
  
          if (acc != null) {
              AccessController.doPrivileged(() -> {
                  //调用ApplicationContextAware 初始化方法
                  this.invokeAwareInterfaces(bean);
                  return null;
              }, acc);
          } else {
              this.invokeAwareInterfaces(bean);
          }
  
          return bean;
      }
      //具体实现
     private void invokeAwareInterfaces(Object bean) {
          if (bean instanceof Aware) {
              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);
              }
              //初始化
              if (bean instanceof ApplicationContextAware) {
                  ((ApplicationContextAware)bean).setApplicationContext(this.applicationContext);
              }
          }
  
      }
  

• 通过上面的代码可以很清楚的了解到ApplicationContextAware实现类在应用启动的时候就会初始化。。。