Spring的@Configuration使用与原理

package com.morris.spring.config; import com.morris.spring.entity.Message; import com.morris.spring.entity.Order; import com.morris.spring.entity.User; import org.springframework.context.annotation.Bean; import org.springframework.context.annotation.Configuration; import org.springframework.stereotype.Component; //@Component @Configuration public class UserConfig { @Bean public User user() { System.out.println("create user"); return new User(); } @Bean public Message message() { return new Message(user()); } }

public static boolean checkConfigurationClassCandidate( BeanDefinition beanDef, MetadataReaderFactory metadataReaderFactory) { ... ... Map config = metadata.getAnnotationAttributes(Configuration.class.getName()); if (config != null && !Boolean.FALSE.equals(config.get("proxyBeanMethods"))) { // 这里对@Configuration做了特殊处理，往BD中设置了属性full beanDef.setAttribute(CONFIGURATION_CLASS_ATTRIBUTE, CONFIGURATION_CLASS_FULL); } else if (config != null || isConfigurationCandidate(metadata)) { // 带有@Component、@ComponentScan、@Import、@ImportResource、@Bean注解的BD，设置属性lite beanDef.setAttribute(CONFIGURATION_CLASS_ATTRIBUTE, CONFIGURATION_CLASS_LITE); } else { return false; } // It's a full or lite configuration candidate... Let's determine the order value, if any. Integer order = getOrder(metadata); if (order != null) { beanDef.setAttribute(ORDER_ATTRIBUTE, order); } return true; }

... Set beanMethods = retrieveBeanMethodMetadata(sourceClass); for (MethodMetadata methodMetadata : beanMethods) { configClass.addBeanMethod(new BeanMethod(methodMetadata, configClass)); } ...

private void loadBeanDefinitionsForBeanMethod(BeanMethod beanMethod) { ConfigurationClass configClass = beanMethod.getConfigurationClass(); MethodMetadata metadata = beanMethod.getMetadata(); String methodName = metadata.getMethodName(); ... ... if (metadata.isStatic()) { // static @Bean method // 静态 @Bean method if (configClass.getMetadata() instanceof StandardAnnotationMetadata) { beanDef.setBeanClass(((StandardAnnotationMetadata) configClass.getMetadata()).getIntrospectedClass()); } else { beanDef.setBeanClassName(configClass.getMetadata().getClassName()); } beanDef.setUniqueFactoryMethodName(methodName); } else { // 实例 @Bean method // instance @Bean method beanDef.setFactoryBeanName(configClass.getBeanName()); beanDef.setUniqueFactoryMethodName(methodName); } ...	... this.registry.registerBeanDefinition(beanName, beanDefToRegister); }

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); if (!this.registriesPostProcessed.contains(factoryId)) { // BeanDefinitionRegistryPostProcessor hook apparently not supported... // Simply call processConfigurationClasses lazily at this point then. processConfigBeanDefinitions((BeanDefinitionRegistry) beanFactory); } // 对@Configuration注解的类做增强，CGlib代理 enhanceConfigurationClasses(beanFactory); beanFactory.addBeanPostProcessor(new ImportAwareBeanPostProcessor(beanFactory)); } public void enhanceConfigurationClasses(ConfigurableListableBeanFactory beanFactory) { Map configBeanDefs = new LinkedHashMap<>(); // 收集所有带有@Configuration的BD，也就是有个attribute为full的属性 for (String beanName : beanFactory.getBeanDefinitionNames()) { BeanDefinition beanDef = beanFactory.getBeanDefinition(beanName); Object configClassAttr = beanDef.getAttribute(ConfigurationClassUtils.CONFIGURATION_CLASS_ATTRIBUTE); MethodMetadata methodMetadata = null; if (beanDef instanceof AnnotatedBeanDefinition) { methodMetadata = ((AnnotatedBeanDefinition) beanDef).getFactoryMethodMetadata(); } if ((configClassAttr != null || methodMetadata != null) && beanDef instanceof AbstractBeanDefinition) { // Configuration class (full or lite) or a configuration-derived @Bean method // -> resolve bean class at this point... AbstractBeanDefinition abd = (AbstractBeanDefinition) beanDef; if (!abd.hasBeanClass()) { try { abd.resolveBeanClass(this.beanClassLoader); } catch (Throwable ex) { throw new IllegalStateException( "Cannot load configuration class: " + beanDef.getBeanClassName(), ex); } } } if (ConfigurationClassUtils.CONFIGURATION_CLASS_FULL.equals(configClassAttr)) { 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'."); } configBeanDefs.put(beanName, (AbstractBeanDefinition) beanDef); } } if (configBeanDefs.isEmpty()) { // nothing to enhance -> return immediately return; } ConfigurationClassEnhancer enhancer = new ConfigurationClassEnhancer(); // 遍历所有带有@Configuration的BD for (Map.Entry 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); // Set enhanced subclass of the user-specified bean class Class configClass = beanDef.getBeanClass(); // 生成CGlib代理类 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())); } beanDef.setBeanClass(enhancedClass); } } }

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 " + "). This is harmless, but you may " + "want check your configuration and remove one CCPP if possible", configClass.getName())); } return configClass; } // 创建代理类 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) { Enhancer enhancer = new Enhancer(); enhancer.setSuperclass(configSuperClass); enhancer.setInterfaces(new Class[] {EnhancedConfiguration.class}); enhancer.setUseFactory(false); enhancer.setNamingPolicy(SpringNamingPolicy.INSTANCE); enhancer.setStrategy(new BeanFactoryAwareGeneratorStrategy(classLoader)); // 这里会注入几个Callback enhancer.setCallbackFilter(CALLBACK_FILTER); enhancer.setCallbackTypes(CALLBACK_FILTER.getCallbackTypes()); return enhancer; } private Class createClass(Enhancer enhancer) { Class subclass = enhancer.createClass(); // Registering callbacks statically (as opposed to thread-local) // is critical for usage in an OSGi environment (SPR-5932)... Enhancer.registerStaticCallbacks(subclass, CALLBACKS); return subclass; } private static final Callback[] CALLBACKS = new Callback[] { new BeanMethodInterceptor(), // 重点 new BeanFactoryAwareMethodInterceptor(), NoOp.INSTANCE }; private static final ConditionalCallbackFilter CALLBACK_FILTER = new ConditionalCallbackFilter(CALLBACKS);

public Object intercept(Object enhancedConfigInstance, Method beanMethod, Object[] beanMethodArgs, MethodProxy cglibMethodProxy) throws Throwable { ConfigurableBeanFactory beanFactory = getBeanFactory(enhancedConfigInstance); 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. 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 return enhanceFactoryBean(factoryBean, beanMethod.getReturnType(), beanFactory, beanName); } } 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())); } // 第一次调用走这 return cglibMethodProxy.invokeSuper(enhancedConfigInstance, beanMethodArgs); } // 第二次调用走这 return resolveBeanReference(beanMethod, beanMethodArgs, beanFactory, beanName); }

private boolean isCurrentlyInvokedFactoryMethod(Method method) { // SimpleInstantiationStrategy这个值哪里设置进去的 /** * @see SimpleInstantiationStrategy#instantiate(org.springframework.beans.factory.support.RootBeanDefinition, java.lang.String, org.springframework.beans.factory.BeanFactory, java.lang.Object, java.lang.reflect.Method, java.lang.Object...) */ Method currentlyInvoked = SimpleInstantiationStrategy.getCurrentlyInvokedFactoryMethod(); return (currentlyInvoked != null && method.getName().equals(currentlyInvoked.getName()) && Arrays.equals(method.getParameterTypes(), currentlyInvoked.getParameterTypes())); }

... try { // 放入ThreadLocal，@Bean走cglib代理会使用这个ThreadLocal currentlyInvokedFactoryMethod.set(factoryMethod); Object result = factoryMethod.invoke(factoryBean, args); if (result == null) { result = new NullBean(); } return result; } ...

private Object resolveBeanReference(Method beanMethod, Object[] beanMethodArgs, ConfigurableBeanFactory beanFactory, String beanName) { // The user (i.e. not the factory) is requesting this bean through a call to // the bean method, direct or indirect. The bean may have already been marked // as 'in creation' in certain autowiring scenarios; if so, temporarily set // the in-creation status to false in order to avoid an exception. boolean alreadyInCreation = beanFactory.isCurrentlyInCreation(beanName); try { if (alreadyInCreation) { beanFactory.setCurrentlyInCreation(beanName, false); } boolean useArgs = !ObjectUtils.isEmpty(beanMethodArgs); if (useArgs && beanFactory.isSingleton(beanName)) { // Stubbed null arguments just for reference purposes, // expecting them to be autowired for regular singleton references? // A safe assumption since @Bean singleton arguments cannot be optional... for (Object arg : beanMethodArgs) { if (arg == null) { useArgs = false; break; } } } // 第二次调用直接从BeanFactory中取 Object beanInstance = (useArgs ? beanFactory.getBean(beanName, beanMethodArgs) : beanFactory.getBean(beanName)); if (!ClassUtils.isAssignableValue(beanMethod.getReturnType(), beanInstance)) { // Detect package-protected NullBean instance through equals(null) check if (beanInstance.equals(null)) { if (logger.isDebugEnabled()) { logger.debug(String.format("@Bean method %s.%s called as bean reference " + "for type [%s] returned null bean; resolving to null value.", beanMethod.getDeclaringClass().getSimpleName(), beanMethod.getName(), beanMethod.getReturnType().getName())); } beanInstance = null; } else { String msg = String.format("@Bean method %s.%s called as bean reference " + "for type [%s] but overridden by non-compatible bean instance of type [%s].", beanMethod.getDeclaringClass().getSimpleName(), beanMethod.getName(), beanMethod.getReturnType().getName(), beanInstance.getClass().getName()); try { BeanDefinition beanDefinition = beanFactory.getMergedBeanDefinition(beanName); msg += " Overriding bean of same name declared in: " + beanDefinition.getResourceDescription(); } catch (NoSuchBeanDefinitionException ex) { // Ignore - simply no detailed message then. } throw new IllegalStateException(msg); } } Method currentlyInvoked = SimpleInstantiationStrategy.getCurrentlyInvokedFactoryMethod(); if (currentlyInvoked != null) { String outerBeanName = BeanAnnotationHelper.determineBeanNameFor(currentlyInvoked); beanFactory.registerDependentBean(beanName, outerBeanName); } return beanInstance; } finally { if (alreadyInCreation) { beanFactory.setCurrentlyInCreation(beanName, true); } } }

package com.morris.spring.config; import com.morris.spring.entity.Message; import com.morris.spring.entity.UserFactoryBean; import org.springframework.context.annotation.Bean; import org.springframework.context.annotation.Configuration; @Configuration public class UserFactoryBeanConfig { @Bean public UserFactoryBean userFactoryBean() { System.out.println("userFactoryBean"); return new UserFactoryBean(); } @Bean public Message message() throws Exception { return new Message(userFactoryBean().getObject()); } }

... 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 // 为FactoryBean创建代理 return enhanceFactoryBean(factoryBean, beanMethod.getReturnType(), beanFactory, beanName); } } ...

private Object enhanceFactoryBean(final Object factoryBean, Class exposedType, final ConfigurableBeanFactory beanFactory, final String beanName) { try { Class clazz = factoryBean.getClass(); boolean finalClass = Modifier.isFinal(clazz.getModifiers()); boolean finalMethod = Modifier.isFinal(clazz.getMethod("getObject").getModifiers()); if (finalClass || finalMethod) { if (exposedType.isInterface()) { if (logger.isTraceEnabled()) { logger.trace("Creating interface proxy for FactoryBean '" + beanName + "' of type [" + clazz.getName() + "] for use within another @Bean method because its " + (finalClass ? "implementation class" : "getObject() method") + " is final: Otherwise a getObject() call would not be routed to the factory."); } // 创建jdk动态代理 return createInterfaceProxyForFactoryBean(factoryBean, exposedType, beanFactory, beanName); } else { if (logger.isDebugEnabled()) { logger.debug("Unable to proxy FactoryBean '" + beanName + "' of type [" + clazz.getName() + "] for use within another @Bean method because its " + (finalClass ? "implementation class" : "getObject() method") + " is final: A getObject() call will NOT be routed to the factory. " + "Consider declaring the return type as a FactoryBean interface."); } return factoryBean; } } } catch (NoSuchMethodException ex) { // No getObject() method -> shouldn't happen, but as long as nobody is trying to call it... } // 使用cglib创建代理 return createCglibProxyForFactoryBean(factoryBean, beanFactory, beanName); }