前言

在Spring中只要被@Configuration注解修饰的类，Spring就会为其生成代理对象，至于这样做的主要原因就是为了解决生成对象的单例问题。

说明

实际上作者在ConfigurationClassEnhancer这个类也有注解说明

场景

如果Spring不做处理，下面输出的一定的是false，但是实际上输出的结果是true，那么只有可能是代理类做了特殊处理。

@Configurationpublic class MyConfiguration {    @Bean    public TestA a(){ return new TestA();    }    @Bean    public TestB b(){ TestA a = a(); TestA b = a(); System.out.println(a == b); return new TestB();    }}

处理分析

生成的代理对象，最终会调用ConfigurationClassEnhancer内部类BeanMethodInterceptor的intercept方法，如果不是当前调用的Bean对象（也就是isCurrentlyInvokedFactoryMethod(beanMethod)返回false），则会调用resolveBeanReference方法。

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-proxyif (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 enhancementreturn 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()));}return cglibMethodProxy.invokeSuper(enhancedConfigInstance, beanMethodArgs);}return resolveBeanReference(beanMethod, beanMethodArgs, beanFactory, beanName);}

此方法会通过getBean来获取对象，这样就可以控制对象的生成了。

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;}}}// 通过getBean就可以控制对象的生成，对象如果生成过，则可以直接从一级缓存中获取Object beanInstance = (useArgs ? beanFactory.getBean(beanName, beanMethodArgs) :beanFactory.getBean(beanName));if (!ClassUtils.isAssignableValue(beanMethod.getReturnType(), beanInstance)) {// Detect package-protected NullBean instance through equals(null) checkif (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);}}}