Spring之ApplicationContextAware使用详解

超、凢脫俗 2024-03-24 14:52 54阅读 0赞

## 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。。。