浅析对Spring aware接口理解

/**
 * 获取spring注入对象方法
 */
@Component("springUtil")
public final class SpringUtil implements ApplicationContextAware {
    /**
     * 应用上下文
     */
    private static ApplicationContext applicationContext;
    /**
     * public方法可能被调用，导致线程不安全。这样写也是为了通过sonar检测
     * @param applicationContext 通过aware设置上下文
     */
    @Override
    public void setApplicationContext(@NonNull ApplicationContext applicationContext) {
        synchronized (SpringUtil.class) {
            if (null == SpringUtil.applicationContext) {
                SpringUtil.applicationContext = applicationContext;
            }
        }
    }

    /**
     * 获取注入对象
     *
     * @param name 对象名称
     * @return 指定注入对象
     */
    public static Object getBean(String name) {
        return getApplicationContext().getBean(name);
    }

    private static ApplicationContext getApplicationContext() {
        return applicationContext;
    }

    /**
     * 获取注入对象
     *
     * @param clazz 对象类型
     * @param <T>   泛型
     * @return 指定注入对象
     */
    public static <T> T getBean(Class<T> clazz) {
        return getApplicationContext().getBean(clazz);
    }

    /**
     * 获取注入对象
     *
     * @param name  对象名称
     * @param clazz 对象类型
     * @param <T>   泛型
     * @return 指定注入对象
     */
    public static <T> T getBean(String name, Class<T> clazz) {
        return getApplicationContext().getBean(name, clazz);
    }
}

public interface TimeAware extends Aware {
    void setTriggerTime(Date date);
}

@Component
public class AwarePostProcessor implements BeanPostProcessor {
    private final ConfigurableApplicationContext applicationContext;
    /**
     * 可写可不写，这个构造是为了获取applicationContext
     */
    public AwarePostProcessor(ConfigurableApplicationContext applicationContext) {
        this.applicationContext = applicationContext;
    }

    @Override
    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        if (bean instanceof Aware) {
            if (bean instanceof TimeAware) {
                // 实现自定义Aware接口的逻辑，设置调用的时间
                ((TimeAware)bean).setTriggerTime(new Date());
            }
        }
        return bean;
    }
}

@Import(AwarePostProcessor.class)
public class Test implements TimeAware {
    Date date;
    @Override
    public void setTriggerTime(Date date) {
        this.date = date;
    }

    public static void main(String[] args) {
        ApplicationContext context = new AnnotationConfigApplicationContext(Test.class);
        Test bean = context.getBean(Test.class);
        System.out.println(bean.date);
    }
}

protected Object initializeBean(String beanName, Object bean, @Nullable RootBeanDefinition mbd) {
		if (System.getSecurityManager() != null) {
			AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
				invokeAwareMethods(beanName, bean);
				return null;
			}, getAccessControlContext());
		}
		else {
			/**
			 * 调用Bean实现的Aware接口的方法，主要包括下面三个接口
			 * BeanNameAware ----> setBeanName()
			 * BeanClassLoaderAware ----> setBeanClassLoader()
			 * BeanFactoryAware  ----> setBeanFactory()
			 */
			invokeAwareMethods(beanName, bean);
		}

		Object wrappedBean = bean;
		if (mbd == null || !mbd.isSynthetic()) {
			/** 调用Bean对象的postProcessBeforeInitialization方法，此处会执行标注@PostConstruct注解的方法 */
			// 此处会调用ApplicationContextAwareProcessor执行其他的aware方法.
			wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
		}

		try {
			/**
			 * 执行Bean的初始化方法:
			 *
			 * 1.先判断Bean是否实现了InitializingBean接口，如果实现了InitializingBean接口，则调用Bean对象的afterPropertiesSet方法；
			 * 2.然后判断Bean是否有指定init-method方法，如果指定了init-method方法，则调用bean对象的init-method指定的方法.
			 */
			invokeInitMethods(beanName, wrappedBean, mbd);
		}
		catch (Throwable ex) {
			throw new BeanCreationException(
					(mbd != null ? mbd.getResourceDescription() : null),
					beanName, "Invocation of init method failed", ex);
		}
		if (mbd == null || !mbd.isSynthetic()) {
			/**
			 * 调用Bean对象的postProcessAfterInitialization方法
			 *
			 * 如果需要创建代理，在该步骤中执行postProcessAfterInitialization方法的时候会去创建代理
			 * 调用AbstractAutoProxyCreator类的postProcessAfterInitialization方法，然后调用wrapIfNecessary方法去创建代理.
			 *
			 *
			 * 另外还有一些Aware接口，也会在该步骤中执行，例如：ApplicationContextAwareProcessor后置处理器，对应的setApplicationContext方法会被执行.
			 */
			wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
		}

		return wrappedBean;
	}

private void invokeAwareMethods(String beanName, Object bean) {
		if (bean instanceof Aware) {
			if (bean instanceof BeanNameAware) {
				((BeanNameAware) bean).setBeanName(beanName);
			}
			if (bean instanceof BeanClassLoaderAware) {
				ClassLoader bcl = getBeanClassLoader();
				if (bcl != null) {
					((BeanClassLoaderAware) bean).setBeanClassLoader(bcl);
				}
			}
			if (bean instanceof BeanFactoryAware) {
				((BeanFactoryAware) bean).setBeanFactory(AbstractAutowireCapableBeanFactory.this);
			}
		}
	}

private void invokeAwareInterfaces(Object bean) {
		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);
		}
		if (bean instanceof ApplicationContextAware) {
			((ApplicationContextAware) bean).setApplicationContext(this.applicationContext);
		}
	}