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Today, the editor will share with you the relevant knowledge of what is the reason for the class generation agent modified by the @ Configuration annotation in Spring. The content is detailed and the logic is clear. I believe most people still know too much about this knowledge, so share this article for your reference. I hope you can get something after reading this article.

Preface

Spring generates a proxy object for any class in Spring that is modified by the @ Configuration annotation, and the main reason for this is to solve the singleton problem of generating objects.

Description

In fact, the author also has notes in the ConfigurationClassEnhancer class.

Scene

If the Spring does not do processing, the output below must be false, but the actual output is true, then it is only possible that the proxy class has done special handling.

@ 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 ();}} processing and analysis

The generated proxy object will eventually call the intercept method of the ConfigurationClassEnhancer inner class BeanMethodInterceptor, and if it is not the currently called Bean object (that is, isCurrentlyInvokedFactoryMethod (beanMethod) returns false), the resolveBeanReference method will be called.

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

This method gets the object through getBean, so you can control the generation of the object.

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 You can control the generation of objects through getBean. If an object has been generated, you can get Object beanInstance = (useArgs?) directly from the first-level cache. 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);} above is "what is the reason for the class generation agent modified by @ Configuration annotation in Spring", thank you for reading! I believe you will gain a lot after reading this article. The editor will update different knowledge for you every day. If you want to learn more knowledge, please pay attention to the industry information channel.

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