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This article mainly introduces the relevant knowledge of how BeanPostProcessor is applied in spring, the content is detailed and easy to understand, the operation is simple and fast, and it has a certain reference value. I believe you will gain something after reading this article on how to apply BeanPostProcessor in spring. Let's take a look at it.

Principle of 1.BeanPostProcessor implementation

1) View the code at breakpoint

1. Add breakpoints in MyBeanPostProcessor and run the test method to view the execution flow by observing the stack

The long English below is the window in the lower right corner of debugging:

2.: 84, AnnotationConfigApplicationContext initializes the container

Public AnnotationConfigApplicationContext (Class... AnnotatedClasses) {this (); register (annotatedClasses); refresh ();} 3. Refresh:543, AbstractApplicationContext calls the refresh () function to instantiate all remaining singletons

/ / Instantiate all remaining (non-lazy-init) singletons. FinishBeanFactoryInitialization (beanFactory); 4. FinishBeanFactoryinitialization: 867, AbstractApplicationContext

/ / Instantiate all remaining (non-lazy-init) singletons. BeanFactory.preInstantiateSingletons (); preInstantiateSingletons:761, DefaultListableBeanFactory, initialize the remaining BeangetBean (beanName) through the getBean function; 5. DoGetBean:302, AbstractBeanFactory: get a single instance through getSingleton, and create Bean// Create bean instance by initializing the createBean method. If (mbd.isSingleton ()) {sharedInstance = getSingleton (beanName, new ObjectFactory () {@ Override public Object getObject () throws BeansException {try {return createBean (beanName, mbd, args) } catch (BeansException ex) {/ / Explicitly remove instance from singleton cache: It might have been put there / / eagerly by the creation process, to allow for circular reference resolution. / / Also remove any beans that received a temporary reference to the bean. DestroySingleton (beanName); throw ex;}); bean = getObjectForBeanInstance (sharedInstance, name, beanName, mbd);} 6. CreateBean:483, AbstractAutowireCapableBeanFactory, call initialization to get Bean instance

Object beanInstance = doCreateBean (beanName, mbdToUse, args); 7. DoCreateBean:555, AbstractAutowireCapableBeanFactory go to the concrete creation Bean and fill Bean via populateBean () Object exposedObject = bean; try {populateBean (beanName, mbd, instanceWrapper); if (exposedObject! = null) {exposedObject = initializeBean (beanName, exposedObject, mbd);}} 8. Finally, you can see that initializeBean:1620, execute applyBeanPostProcessorsBeforeInitialization and applyBeanPostProcessorsAfterInitialization in AbstractAutowireCapableBeanFactory to call postProcessBeforeInitialization () function and postProcessAfterInitialization () function; call invokeInitMethods (beanName, wrappedBean, mbd) in the middle; Object wrappedBean = bean; if (mbd = = null | |! mbd.isSynthetic ()) {wrappedBean = applyBeanPostProcessorsBeforeInitialization (wrappedBean, beanName);}

Try {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 ()) {wrappedBean = applyBeanPostProcessorsAfterInitialization (wrappedBean, beanName);}

Object result = existingBean; for (BeanPostProcessor beanProcessor: getBeanPostProcessors ()) {result = beanProcessor.postProcessBeforeInitialization (result, beanName); if (result = = null) {return result;}} return result;} 2) summarize the execution principle in the process of operation

By looking at the breakpoint debugging results, you can see that creating a singleton container Bean is populated by the populateBean () function, invokeInitMethods (beanName, wrappedBean, mbd)

Function is initialized, and then applyBeanPostProcessorsBeforeInitialization and applyBeanPostProcessorsAfterInitialization perform all BeanPostProcessor scans before and after.

Application of 2.BeanPostProcessor in spring

BeanPostProcessor is widely used in spring for processing. Here are three examples for breakpoint and code testing: 1) .ApplicationContextAwareProcessor help component injection into the IOC container to implement the implements ApplicationContextAware interface in Dog, write, setApplicationContext saves the container to the property method @ Componentpublic class Dog implements ApplicationContextAware {private ApplicationContext applicationContext

Public Dog () {System.out.println ("dog constructor...");}

@ Override public void setApplicationContext (ApplicationContext applicationContext) throws BeansException {/ / TODO Auto-generated method stub this.applicationContext = applicationContext;}} 1. PostProcessBeforeInitialization:97,ApplicationContextAwareProcessor can see that the container is assigned through the postProcessBeforeInitialization function

two。 Judge the type of Bean by invokeAwareInterfaces, convert the type and assign the value.

Private void invokeAwareInterfaces (Object bean) {if (bean instanceof Aware) {if (bean instanceof EnvironmentAware) {((EnvironmentAware) bean) .setEnvironment (this.applicationContext.getEnvironment ());} if (bean instanceof EmbeddedValueResolverAware) {((EmbeddedValueResolverAware) bean) .setEmbeddedValueResolver (this.embeddedValueResolver);} if (bean instanceof ResourceLoaderAware) {((ResourceLoaderAware) bean) .setResourceLoader (this.applicationContext) } if (bean instanceof ApplicationEventPublisherAware) {((ApplicationEventPublisherAware) bean) .setApplicationEventPublisher (this.applicationContext);} if (bean instanceof MessageSourceAware) {((MessageSourceAware) bean) .setMessageSource (this.applicationContext);} if (bean instanceof ApplicationContextAware) {((ApplicationContextAware) bean) .setApplicationContext (this.applicationContext);} 2) .InitDestroyAnnotationBeanPostProcessor is used to process @ PostConstruct and @ PreDestroy annotations. View the InitDestroyAnnotationBeanPostProcessor source code and postProcessBeforeInitialization function code as follows: @ Override public Object postProcessBeforeInitialization (Object bean, String beanName) throws BeansException {LifecycleMetadata metadata = findLifecycleMetadata (bean.getClass ()); try {metadata.invokeInitMethods (bean, beanName);} catch (InvocationTargetException ex) {throw new BeanCreationException (beanName, "Invocation of init method failed", ex.getTargetException ());} catch (Throwable ex) {throw new BeanCreationException (beanName, "Failed to invoke init method", ex) } return bean;} use findLifecycleMetadata (bean.getClass ()); get all the lifecycle functions through metadata.invokeInitMethods (bean, beanName); call the corresponding lifecycle function public void invokeInitMethods (Object target, String beanName) throws Throwable {Collection initMethodsToIterate = (this.checkedInitMethods! = null? This.checkedInitMethods: this.initMethods); if (! initMethodsToIterate.isEmpty ()) {boolean debug = logger.isDebugEnabled (); for (LifecycleElement element: initMethodsToIterate) {if (debug) {logger.debug ("Invoking init method on bean'" + beanName + "':" + element.getMethod ());} element.invoke (target) } 3). BeanValidationPostProcessor data verification is used for data verification. Check the source code postProcessBeforeInitialization and postProcessAfterInitialization code of BeanValidationPostProcessor as follows, and perform doValidate () function for data verification. @ Override public Object postProcessBeforeInitialization (Object bean, String beanName) throws BeansException {if (! this.afterInitialization) {doValidate (bean);} return bean;}

@ Override public Object postProcessAfterInitialization (Object bean, String beanName) throws BeansException {if (this.afterInitialization) {doValidate (bean);} return bean;}

This is the end of the article on "how to use BeanPostProcessor in spring". Thank you for reading! I believe that everyone has a certain understanding of the knowledge of "how to apply BeanPostProcessor in spring". If you want to learn more knowledge, you are welcome to follow the industry information channel.

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