How does ApplicationContextAware work in Spring

Question

In spring  if a bean implements ApplicationContextAware  then it is able to access the applicationContext  Therefore it is able to get other beans  e g    public class SpringContextUtil implements ApplicationContextAware       private static ApplicationContext applicationContext            public void setApplicationContext ApplicationContext context  throws BeansException         applicationContext   context             public static ApplicationContext getApplicationContext           return applicationContext            Then SpringContextUtil getApplicationContext getBean  name   can get the bean  name    To do this  we should put this SpringContextUtil inside the applications xml  e g    lt bean class  com util SpringContextUtil    gt    Here the bean SpringContextUtil doesn t include the property applicationContext  I guess when spring bean initialize  this property is set  But how is this done  How does the method setApplicationContext get called

User · Answer

ApplicationContextAware Interface  the current application context  through which you can invoke the spring container services  We can get current applicationContext instance injected by below method in the class  public void setApplicationContext ApplicationContext context  throws BeansException

User · Answer

Interface to be implemented by any object that wishes to be notified of the ApplicationContext that it runs in    above is excerpted from the Spring doc website https   docs spring io spring-framework docs current javadoc-api org springframework context ApplicationContextAware html   So  it seemed to be invoked when Spring container has started  if you want to do something at that time   It just has one method to set the context  so you will get the context and do something to sth now already in context I think

User · Answer

Spring source code to explain how  ApplicationContextAware work when you use ApplicationContext context   new ClassPathXmlApplicationContext  applicationContext xml    In AbstractApplicationContext class the refresh   method have the following code        Prepare the bean factory for use in this context  prepareBeanFactory beanFactory     enter this method beanFactory addBeanPostProcessor new ApplicationContextAwareProcessor this    will add ApplicationContextAwareProcessor to AbstractrBeanFactory   protected void prepareBeanFactory ConfigurableListableBeanFactory beanFactory               Tell the internal bean factory to use the context s class loader etc          beanFactory setBeanClassLoader getClassLoader             beanFactory setBeanExpressionResolver new StandardBeanExpressionResolver beanFactory getBeanClassLoader              beanFactory addPropertyEditorRegistrar new ResourceEditorRegistrar this  getEnvironment                 Configure the bean factory with context callbacks          beanFactory addBeanPostProcessor new ApplicationContextAwareProcessor this                  When spring initialize bean in AbstractAutowireCapableBeanFactory  in method initializeBean call applyBeanPostProcessorsBeforeInitialization to implement the bean post process  the process include inject the applicationContext    Override     public Object applyBeanPostProcessorsBeforeInitialization Object existingBean  String beanName              throws BeansException           Object result   existingBean          for  BeanPostProcessor beanProcessor   getBeanPostProcessors                  result   beanProcessor postProcessBeforeInitialization result  beanName               if  result    null                    return result                                  return result          when BeanPostProcessor implement Objectto execute the postProcessBeforeInitialization method for example ApplicationContextAwareProcessor that added before   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                          new EmbeddedValueResolver this applicationContext getBeanFactory                                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

User · Answer

When spring instantiates beans  it looks for a couple of interfaces like ApplicationContextAware and InitializingBean  If they are found  the methods are invoked  E g   very simplified   Class lt   gt  beanClass   beanDefinition getClass    Object bean   beanClass newInstance    if  bean instanceof ApplicationContextAware          ApplicationContextAware  bean  setApplicationContext ctx       Note that in newer version it may be better to use annotations  rather than implementing spring-specific interfaces  Now you can simply use    Inject    or  Autowired private ApplicationContext ctx

[java] How does ApplicationContextAware work in Spring?

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