[Java知识库]Spring源码分析 (Aware接口调用) (八)

Aware接口是利用的回调机制, 将资源注入ioc容器

1.Aware是什么时候赋值进来的

1.createBeanInstance实例化 bean 2.populateBean属性注入 3.initializingBean初始化对象
createBeanInstance:getBean -> doGetBean -> createBean -> doCreateBean
initializingBean初始化对象: 1.激活Aware 2.后置处理器的应用 3.init方法

所以说Aware接口是在initializingBean初始化对象的第一步执行的。

2.Aware接口的作用

Aware接口帮装配Spring底层的一些组件

调用setApplicationContext方法注入

3.Aware接口如何调用

ApplicationContextAwareProcessor.postProcessorBeforeInitialization() -> invokeAwareInterfaces()

4.测试

@Component
public class Cat implements ApplicationContextAware {
    private String catName = "tomcat";

    private ApplicationContext context;

    public Cat() {
        System.out.println("cat创建");
    }

    public String getCatName() {
        return catName;
    }

    public void setCatName(String catName) {
        this.catName = catName;
    }

    public ApplicationContext getContext() {
        return context;
    }

    public void setContext(ApplicationContext context) {
        this.context = context;
    }

    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        this.context = applicationContext;
    }
}

@Configuration
@ComponentScan("com.zzz.a7")
public class MainConfig {

}

public class MainTest {
    public static void main(String[] args) {
        ApplicationContext applicationContext = new AnnotationConfigApplicationContext(MainConfig.class);

        Cat bean = applicationContext.getBean(Cat.class);
        ApplicationContext context = bean.getContext();

        System.out.println(applicationContext == context);
    }
}

5.执行流程

1. AnnotationConfigApplicationContext.java

2. AbstractApplicationContext.java
   refresh.finishBeanFactoryInitialization()

	protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {
		// Initialize conversion service for this context.
		if (beanFactory.containsBean(CONVERSION_SERVICE_BEAN_NAME) &&
				beanFactory.isTypeMatch(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class)) {
			beanFactory.setConversionService(
					beanFactory.getBean(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class));
		}

		// Register a default embedded value resolver if no BeanFactoryPostProcessor
		// (such as a PropertySourcesPlaceholderConfigurer bean) registered any before:
		// at this point, primarily for resolution in annotation attribute values.
		if (!beanFactory.hasEmbeddedValueResolver()) {
			beanFactory.addEmbeddedValueResolver(strVal -> getEnvironment().resolvePlaceholders(strVal));
		}

		// Initialize LoadTimeWeaverAware beans early to allow for registering their transformers early.
		String[] weaverAwareNames = beanFactory.getBeanNamesForType(LoadTimeWeaverAware.class, false, false);
		for (String weaverAwareName : weaverAwareNames) {
			getBean(weaverAwareName);
		}

		// Stop using the temporary ClassLoader for type matching.
		beanFactory.setTempClassLoader(null);

		// Allow for caching all bean definition metadata, not expecting further changes.
		beanFactory.freezeConfiguration();

		// Instantiate all remaining (non-lazy-init) singletons.
		beanFactory.preInstantiateSingletons();
	}

3. DefaultListableBeanFactory.java
   beanFactory.preInstantiateSingletons()

	@Override
	public void preInstantiateSingletons() throws BeansException {
		if (logger.isTraceEnabled()) {
			logger.trace("Pre-instantiating singletons in " + this);
		}

		// Iterate over a copy to allow for init methods which in turn register new bean definitions.
		// While this may not be part of the regular factory bootstrap, it does otherwise work fine.
		List<String> beanNames = new ArrayList<>(this.beanDefinitionNames);

		// Trigger initialization of all non-lazy singleton beans...
		for (String beanName : beanNames) {
			RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
			if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
				if (isFactoryBean(beanName)) {
					Object bean = getBean(FACTORY_BEAN_PREFIX + beanName);
					if (bean instanceof FactoryBean) {
						FactoryBean<?> factory = (FactoryBean<?>) bean;
						boolean isEagerInit;
						if (System.getSecurityManager() != null && factory instanceof SmartFactoryBean) {
							isEagerInit = AccessController.doPrivileged(
									(PrivilegedAction<Boolean>) ((SmartFactoryBean<?>) factory)::isEagerInit,
									getAccessControlContext());
						}
						else {
							isEagerInit = (factory instanceof SmartFactoryBean &&
									((SmartFactoryBean<?>) factory).isEagerInit());
						}
						if (isEagerInit) {
							getBean(beanName);
						}
					}
				}
				else {
					getBean(beanName);
				}
			}
		}

4. DefaultListableBeanFactory.java
   getBean()

5. AbstractBeanFactory
   doGetBean()
   
6. DefaultSingletonBeanRegistry.java
   getSingleton()

	@Nullable
	protected Object getSingleton(String beanName, boolean allowEarlyReference) {
		// Quick check for existing instance without full singleton lock
		Object singletonObject = this.singletonObjects.get(beanName);
		if (singletonObject == null && isSingletonCurrentlyInCreation(beanName)) {
			singletonObject = this.earlySingletonObjects.get(beanName);
			if (singletonObject == null && allowEarlyReference) {
				synchronized (this.singletonObjects) {
					// Consistent creation of early reference within full singleton lock
					singletonObject = this.singletonObjects.get(beanName);
					if (singletonObject == null) {
						singletonObject = this.earlySingletonObjects.get(beanName);
						if (singletonObject == null) {
							ObjectFactory<?> singletonFactory = this.singletonFactories.get(beanName);
							if (singletonFactory != null) {
								singletonObject = singletonFactory.getObject();
								this.earlySingletonObjects.put(beanName, singletonObject);
								this.singletonFactories.remove(beanName);
							}
						}
					}
				}
			}
		}
		return singletonObject;
	}

这里有三级缓存的一些池。

7. AbstractAutowireCapableBeanFactory.java
   createBean -> doCreateBean() -> createBeanInstance()/initializeBean() -> applyBeanPostProcessorsBeforeInitialization() -> postProcessBeforeInitialization()

8. ApplicationContextAwareProcessor.java
   postProcessBeforeInitialization() -> invokeAwareInterfaces()

	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 ApplicationStartupAware) {
			((ApplicationStartupAware) bean).setApplicationStartup(this.applicationContext.getApplicationStartup());
		}
		if (bean instanceof ApplicationContextAware) {
			((ApplicationContextAware) bean).setApplicationContext(this.applicationContext);
		}
	}

这里是各个Aware的接口

9. 最后通过看实现了哪个接口, 然后调用setApplicationContext方法注入

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