SpringBeanPostProcessor源码示例解析

public interface BeanPostProcessor {
	@Nullable
	default Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
		return bean;
	}
	@Nullable
	default Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
		return bean;
	}
}

@Service
public class UserService {
    private String name = "陈tom";
    private int age;
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
}

@Component
public class MyPostProcessor implements BeanPostProcessor {
    @Override
    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        if ("userService".equals(beanName)) {
            UserService userService = (UserService) bean;
            userService.setName("陈汤姆");
            userService.setAge(21);
        }
        return bean;
    }
    @Override
    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        return BeanPostProcessor.super.postProcessAfterInitialization(bean, beanName);
    }
}

@SpringBootApplication
public class BootApplication {
    @Resource
    private DefaultListableBeanFactory defaultListableBeanFactory;
    public static void main(String[] args) {
        SpringApplication.run(BootApplication.class,args);
    }
    @PostConstruct
    public void init() {
        UserService userService = defaultListableBeanFactory.getBean("userService", UserService.class);
        System.out.println("测试结果：姓名："+userService.getName()+";年龄："+userService.getAge());
    }
}

public abstract class AbstractBeanFactory extends FactoryBeanReGIStrySupport implements ConfigurableBeanFactory {
	//存储BeanPostProcessor列表
	private final List<BeanPostProcessor> beanPostProcessors = new CopyOnWriteArrayList<>();
	@Override
	public void addBeanPostProcessor(BeanPostProcessor beanPostProcessor) {
		Assert.notNull(beanPostProcessor, "BeanPostProcessor must not be null");
		// Remove from old position, if any
		this.beanPostProcessors.remove(beanPostProcessor);
		// Track whether it is instantiation/destruction aware
		if (beanPostProcessor instanceof InstantiationAwareBeanPostProcessor) {
			this.hasInstantiationAwareBeanPostProcessors = true;
		}
		if (beanPostProcessor instanceof DestructionAwareBeanPostProcessor) {
			this.hasDestructionAwareBeanPostProcessors = true;
		}
		// 将BeanPostProcessor加入beanPostProcessors列表中
		this.beanPostProcessors.add(beanPostProcessor);
	}
}

public abstract class AbstractAutowireCapableBeanFactory extends AbstractBeanFactory
		implements AutowireCapableBeanFactory {
	//初始化Bean
	protected Object initializeBean(final String beanName, final 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()) {
			//调用BeanPostProcesso#postProcessBeforeInitialization：前置处理
			wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
		}
		try {
			//执行初始化方法
			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()) {
			//调用调用BeanPostProcesso#postProcessAfterInitialization：后置处理
			wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
		}
		return wrappedBean;
	}
	//BeanPostProcessor前置逻辑处理
	@Override
	public Object applyBeanPostProcessorsBeforeInitialization(Object existingBean, String beanName)
			throws BeansException {
		Object result = existingBean;
		for (BeanPostProcessor processor : getBeanPostProcessors()) {
			//执行实现BeanPostProcessor的实现类的前置增强逻辑
			Object current = processor.postProcessBeforeInitialization(result, beanName);
			if (current == null) {
				return result;
			}
			result = current;
		}
		return result;
	}
	//BeanPostProcessor后置逻辑处理
	@Override
	public Object applyBeanPostProcessorsAfterInitialization(Object existingBean, String beanName)
			throws BeansException {
		Object result = existingBean;
		for (BeanPostProcessor processor : getBeanPostProcessors()) {
			//执行实现BeanPostProcessor的实现类的后置增强逻辑
			Object current = processor.postProcessAfterInitialization(result, beanName);
			if (current == null) {
				return result;
			}
			result = current;
		}
		return result;
	}
}