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。。。