Spring扩展点系列-BeanFactoryAware

文章目录

• • 简介
  • 源码分析
  • 示例代码
  • • 示例一：验证BeanFactoryAware执行顺序
    • 示例二：动态获取其他bean
    • 示例三：动态bean的状态

简介

BeanFactoryAware用于注入BeanFactory对象。我们可以访问创建该对象的BeanFactory 。借助 setBeanFactory()方法，我们将IoC 容器中的BeanFactory引用分配给beanFactory 属性，之后，我们可以创建函数直接使用它。
BeanNameAware的常用场景一般是用于日志记录。

源码分析

BeanFactoryAware是Aware的超级子接口

从源码中可以看到BeanFactoryAware只提供了一个set方法，该接口中只定义了setBeanFactory一个方法。

public interface BeanFactoryAware extends Aware {

	void setBeanFactory(BeanFactory beanFactory) throws BeansException;

}

org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#initializeBean实现了Spring的Aware接口族的Beans（如BeanNameAware, BeanFactoryAware等）。如果提供的bean实现了任何这些接口，该方法会回调相应的Aware方法

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 {
		invokeAwareMethods(beanName, bean);
	}

	Object wrappedBean = bean;
	if (mbd == null || !mbd.isSynthetic()) {
		wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
	}

	try {
		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()) {
		wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
	}

	return wrappedBean;
}

当一个 bean 实现了如 BeanNameAware、BeanClassLoaderAware 或 BeanFactoryAware 等接口时，此方法确保正确的回调方法被调用，从而为 bean 提供关于其运行环境或其他相关信息。

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);
		}
	}
}

示例代码

示例一：验证BeanFactoryAware执行顺序

这里创建一个类去实现BeanFactoryAware，顺带也实现 BanNameAware接口，这样可以比对看出两者的执行顺序

@Slf4j
@Component
public class ExtendBeanFactoryAware implements BeanNameAware, BeanFactoryAware {
    @Override
    public void setBeanName(String name) {
        log.info("ExtendBeanNameAware-2--beanName:{}",name);
    }

    @Override
    public void setBeanFactory(BeanFactory beanFactory) throws BeansException {
        log.info("ExtendBeanFactoryAware-3--beanName:{}",beanFactory);
    }
}

注：如果把@Component缓存@Configuration，setBeanFactory会执行两次。setBeanFactory-》setBeanName=》setBeanFactory
运行示例

示例二：动态获取其他bean

下面这个示例主要展示一个常用的场景，一个 Bean 可以在运行时动态获取其他 Bean

@Slf4j
@Component
public class ExtendBeanFactoryAware implements BeanNameAware, BeanFactoryAware {

	private BeanFactory beanFactory;

    @Override
    public void setBeanFactory(BeanFactory beanFactory) throws BeansException {
    	this.beanFactory = beanFactory;
        log.info("ExtendBeanFactoryAware-3--beanName:{}",beanFactory);
    }

	public void getOtherBean() {
        OtherBean otherBean = beanFactory.getBean(OtherBean.class);
        System.out.println("获取 otherBean 实例: " + otherBean);
    }
}


@Component
public class OtherBean {

    @Override
    public String toString() {
        return "这是 OtherBean 实例";
    }
}

@Configuration
public class AppConfig {
    @Bean
    public OtherBean getOtherBean () {
        return new OtherBean();
    }

    @Bean
    public ExtendBeanFactoryAware getExtendBeanFactoryAware () {
        return new ExtendBeanFactoryAware();
    }
}

//controller运行调用获取bean
@GetMapping("/getOtherBean")
public void getOtherBean() throws Exception{
    ApplicationContext context = new AnnotationConfigApplicationContext(AppConfig.class);
    ExtendBeanFactoryAware beanFactoryAware = context.getBean(ExtendBeanFactoryAware.class);
    beanFactoryAware.getOtherBean();
}

运行示例

示例三：动态bean的状态

在运行时，可以通过 BeanFactoryAware检查某个 Bean 是否存在或者其状态，下面是代码展示

@Slf4j
@Component
public class ExtendBeanFactoryAware implements BeanNameAware, BeanFactoryAware {

	private BeanFactory beanFactory;

    @Override
    public void setBeanFactory(BeanFactory beanFactory) throws BeansException {
    	this.beanFactory = beanFactory;
        log.info("ExtendBeanFactoryAware-3--beanName:{}",beanFactory);
    }

	public void checkBeanState() {
        boolean exists = beanFactory.containsBean("getOtherBean");
        log.info("otherBean 是否存在: {}" , exists);
    }
}


@Component
public class OtherBean {
}

@Configuration
public class AppConfig {
	//如果不指定Bean名，则默认是bean的名字为方法名
    @Bean
    public OtherBean getOtherBean () {
        return new OtherBean();
    }

    @Bean
    public ExtendBeanFactoryAware getExtendBeanFactoryAware () {
        return new ExtendBeanFactoryAware();
    }
}

//controller运行调用获取bean
@GetMapping("/checkBeanState")
public void checkBeanState() throws Exception{
    ApplicationContext context = new AnnotationConfigApplicationContext(AppConfig.class);
    ExtendBeanFactoryAware beanFactoryAware = context.getBean(ExtendBeanFactoryAware.class);
    beanFactoryAware.checkBeanState();
}

运行示例