Spring5 源码学习 (7) ConfigurationClassPostProcessor (下)

//ConfigurationClassPostProcessor#postProcessBeanFactory源码
public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) {
	int factoryId = System.identityHashCode(beanFactory);
	if (this.factoriesPostProcessed.contains(factoryId)) {
		throw new IllegalStateException(
				"postProcessBeanFactory already called on this post-processor against " + beanFactory);
	}
	this.factoriesPostProcessed.add(factoryId);
	// 在 this.postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) 方法中
	// 调用this.registriesPostProcessed.add(registryId);
	// if条件不成立
	if (!this.registriesPostProcessed.contains(factoryId)) {
		// BeanDefinitionRegistryPostProcessor hook apparently not supported...
		// Simply call processConfigurationClasses lazily at this point then.
		processConfigBeanDefinitions((BeanDefinitionRegistry) beanFactory);
	}

	// 对配置类进行增强
	enhanceConfigurationClasses(beanFactory);
	// 创建 ImportAwareBeanPostProcessor ,来支持 ImportAware ,调用ImportAware.setImportMetadata方法
	beanFactory.addBeanPostProcessor(new ImportAwareBeanPostProcessor(beanFactory));
}

public void enhanceConfigurationClasses(ConfigurableListableBeanFactory beanFactory) {
	Map<String, AbstractBeanDefinition> configBeanDefs = new LinkedHashMap<>();
	//获取所有的BeanDefinitionName,之前已经完成了bean的扫描,这里会获取到所有的beanName
	for (String beanName : beanFactory.getBeanDefinitionNames()) {
		BeanDefinition beanDef = beanFactory.getBeanDefinition(beanName);
		// 校验是否为FullConfigurationClass,也就是是否被标记了 @Configuration
		if (ConfigurationClassUtils.isFullConfigurationClass(beanDef)) {
			if (!(beanDef instanceof AbstractBeanDefinition)) {
				throw new BeanDefinitionStoreException("Cannot enhance @Configuration bean definition '" +
						beanName + "' since it is not stored in an AbstractBeanDefinition subclass");
			} else if (logger.isInfoEnabled() && beanFactory.containsSingleton(beanName)) {
				logger.info("Cannot enhance @Configuration bean definition '" + beanName +
						"' since its singleton instance has been created too early. The typical cause " +
						"is a non-static @Bean method with a BeanDefinitionRegistryPostProcessor " +
						"return type: Consider declaring such methods as 'static'.");
			}
			//如果是FullConfigurationClass,则放到变量configBeanDefs中
			configBeanDefs.put(beanName, (AbstractBeanDefinition) beanDef);
		}
	}
	if (configBeanDefs.isEmpty()) {
		// nothing to enhance -> return immediately
		return;
	}

	ConfigurationClassEnhancer enhancer = new ConfigurationClassEnhancer();
	for (Map.Entry<String, AbstractBeanDefinition> entry : configBeanDefs.entrySet()) {
		AbstractBeanDefinition beanDef = entry.getValue();
		// If a @Configuration class gets proxied, always proxy the target class
		beanDef.setAttribute(AutoProxyUtils.PRESERVE_TARGET_CLASS_ATTRIBUTE, Boolean.TRUE);
		try {
			// Set enhanced subclass of the user-specified bean class
			Class<?> configClass = beanDef.resolveBeanClass(this.beanClassLoader);
			if (configClass != null) {
				// 对 FullConfigurationClass 进行增强
				Class<?> enhancedClass = enhancer.enhance(configClass, this.beanClassLoader);
				if (configClass != enhancedClass) {
					if (logger.isTraceEnabled()) {
						logger.trace(String.format("Replacing bean definition '%s' existing class '%s' with " +
								"enhanced class '%s'", entry.getKey(), configClass.getName(), enhancedClass.getName()));
					}
					//将BeanClass设置为增强后的类
					beanDef.setBeanClass(enhancedClass);
				}
			}
		} catch (Throwable ex) {
			throw new IllegalStateException("Cannot load configuration class: " + beanDef.getBeanClassName(), ex);
		}
	}
}

public Class<?> enhance(Class<?> configClass, @Nullable ClassLoader classLoader) {
	if (EnhancedConfiguration.class.isAssignableFrom(configClass)) {
		if (logger.isDebugEnabled()) {
			logger.debug(String.format("Ignoring request to enhance %s as it has " +
							"already been enhanced. This usually indicates that more than one " +
							"ConfigurationClassPostProcessor has been registered (e.g. via " +
							"<context:annotation-config>). This is harmless, but you may " +
							"want check your configuration and remove one CCPP if possible",
					configClass.getName()));
		}
		return configClass;
	}
	Class<?> enhancedClass = createClass(newEnhancer(configClass, classLoader));
	if (logger.isTraceEnabled()) {
		logger.trace(String.format("Successfully enhanced %s; enhanced class name is: %s",
				configClass.getName(), enhancedClass.getName()));
	}
	return enhancedClass;
}

private Enhancer newEnhancer(Class<?> configSuperClass, @Nullable ClassLoader classLoader) {
	// Spring重新打包了CGLIB（使用Spring专用补丁;仅供内部使用）
	// 这样可避免在应用程序级别或第三方库和框架上与CGLIB的依赖性发生任何潜在冲突
	// https://docs.spring.io/spring/docs/current/javadoc-api/org/springframework/cglib/package-summary.html
	Enhancer enhancer = new Enhancer();
	enhancer.setSuperclass(configSuperClass);
	// 设置需要实现的接口,也就是说,我们的配置类的cglib代理还实现的 EnhancedConfiguration 接口
	enhancer.setInterfaces(new Class<?>[]{EnhancedConfiguration.class});
	enhancer.setUseFactory(false);
	// 设置命名策略
	enhancer.setNamingPolicy(SpringNamingPolicy.INSTANCE);
	// 设置生成器创建字节码策略
	// BeanFactoryAwareGeneratorStrategy 是 CGLIB的DefaultGeneratorStrategy的自定义扩展，主要为了引入BeanFactory字段
	enhancer.setStrategy(new BeanFactoryAwareGeneratorStrategy(classLoader));
	// 设置增强
	enhancer.setCallbackFilter(CALLBACK_FILTER);
	enhancer.setCallbackTypes(CALLBACK_FILTER.getCallbackTypes());
	return enhancer;
}

private static final Callback[] CALLBACKS = new Callback[]{
		// 拦截 @Bean 方法的调用,以确保正确处理@Bean语义
		new BeanMethodInterceptor(),
		// 拦截 BeanFactoryAware#setBeanFactory 的调用
		new BeanFactoryAwareMethodInterceptor(),
		NoOp.INSTANCE
};

@Configuration
@ComponentScan
public class AppConfig {

	@Bean
	public String name() throws Exception {
		getUserBean().getObject();
		return "程序员小黑";
	}


	@Bean
	public FactoryBean getUserBean() {
		return new FactoryBean<UserBean>() {
			@Override
			public UserBean getObject() throws Exception {
				System.out.println("1111");
				return new UserBean("shen", 17);
			}

			@Override
			public Class<?> getObjectType() {
				return UserBean.class;
			}
		};
	}
}

//BeanMethodInterceptor#intercept源码
public Object intercept(Object enhancedConfigInstance, Method beanMethod, Object[] beanMethodArgs,
						MethodProxy cglibMethodProxy) throws Throwable {

	// enhancedConfigInstance 已经是配置类的增强对象了,在增强对象中,有beanFactory字段的
	// 获取增强对象中的beanFactory
	ConfigurableBeanFactory beanFactory = getBeanFactory(enhancedConfigInstance);
	// 获取beanName
	String beanName = BeanAnnotationHelper.determineBeanNameFor(beanMethod);

	// Determine whether this bean is a scoped-proxy
	if (BeanAnnotationHelper.isScopedProxy(beanMethod)) {
		String scopedBeanName = ScopedProxyCreator.getTargetBeanName(beanName);
		if (beanFactory.isCurrentlyInCreation(scopedBeanName)) {
			beanName = scopedBeanName;
		}
	}

	// To handle the case of an inter-bean method reference, we must explicitly check the
	// container for already cached instances.

	// First, check to see if the requested bean is a FactoryBean. If so, create a subclass
	// proxy that intercepts calls to getObject() and returns any cached bean instance.
	// This ensures that the semantics of calling a FactoryBean from within @Bean methods
	// is the same as that of referring to a FactoryBean within XML. See SPR-6602.

	// 检查容器中是否存在对应的 FactoryBean 如果存在,则创建一个增强类
	// 通过创建增强类来代理拦截 getObject（）的调用 , 以确保了FactoryBean的语义
	if (factoryContainsBean(beanFactory, BeanFactory.FACTORY_BEAN_PREFIX + beanName) &&
			factoryContainsBean(beanFactory, beanName)) {
		Object factoryBean = beanFactory.getBean(BeanFactory.FACTORY_BEAN_PREFIX + beanName);
		if (factoryBean instanceof ScopedProxyFactoryBean) {
			// Scoped proxy factory beans are a special case and should not be further proxied
		} else {
			// It is a candidate FactoryBean - go ahead with enhancement
			// 创建增强类,来代理 getObject（）的调用
			// 有两种可选代理方式,cglib 和 jdk
			// Proxy.newProxyInstance(
			//					factoryBean.getClass().getClassLoader(), new Class<?>[]{interfaceType},
			//					(proxy, method, args) -> {
			//						if (method.getName().equals("getObject") && args == null) {
			//							return beanFactory.getBean(beanName);
			//						}
			//						return ReflectionUtils.invokeMethod(method, factoryBean, args);
			//					});
			return enhanceFactoryBean(factoryBean, beanMethod.getReturnType(), beanFactory, beanName);
		}
	}

	// 判断当时执行的方法是否为@Bean方法本身
	// 举个例子 : 如果是直接调用@Bean方法,也就是Spring来调用我们的@Bean方法,则返回true
	// 如果是在别的方法内部,我们自己的程序调用 @Bean方法,则返回false
	if (isCurrentlyInvokedFactoryMethod(beanMethod)) {
		// The factory is calling the bean method in order to instantiate and register the bean
		// (i.e. via a getBean() call) -> invoke the super implementation of the method to actually
		// create the bean instance.
		if (logger.isInfoEnabled() &&
				BeanFactoryPostProcessor.class.isAssignableFrom(beanMethod.getReturnType())) {
			logger.info(String.format("@Bean method %s.%s is non-static and returns an object " +
							"assignable to Spring's BeanFactoryPostProcessor interface. This will " +
							"result in a failure to process annotations such as @Autowired, " +
							"@Resource and @PostConstruct within the method's declaring " +
							"@Configuration class. Add the 'static' modifier to this method to avoid " +
							"these container lifecycle issues; see @Bean javadoc for complete details.",
					beanMethod.getDeclaringClass().getSimpleName(), beanMethod.getName()));
		}
		// 如果返回true,也就是Spring在调用这个方法,那么就去真正执行该方法
		return cglibMethodProxy.invokeSuper(enhancedConfigInstance, beanMethodArgs);
	}

	//否则,则尝试从容器中获取该 Bean 对象
	// 怎么获取呢? 通过调用 beanFactory.getBean 方法
	// 而这个getBean 方法,如果对象已经创建则直接返回,如果还没有创建,则创建,然后放入容器中,然后返回
	return resolveBeanReference(beanMethod, beanMethodArgs, beanFactory, beanName);
}

// BeanFactoryAwareMethodInterceptor#intercept 源码
public Object intercept(Object obj, Method method, Object[] args, MethodProxy proxy) throws Throwable {
	Field field = ReflectionUtils.findField(obj.getClass(), BEAN_FACTORY_FIELD);
	Assert.state(field != null, "Unable to find generated BeanFactory field");
	field.set(obj, args[0]);

	// Does the actual (non-CGLIB) superclass implement BeanFactoryAware?
	// If so, call its setBeanFactory() method. If not, just exit.
	if (BeanFactoryAware.class.isAssignableFrom(ClassUtils.getUserClass(obj.getClass().getSuperclass()))) {
		return proxy.invokeSuper(obj, args);
	}
	return null;
}

System.setProperty(DebuggingClassWriter.DEBUG_LOCATION_PROPERTY, "spring-study/docs/classes");