BeanPostProcessor註冊與Bean生命週期過程

在spring啟動過程中，會有很多次調用getBean方法來創建或獲取bean實例

@Override

public Object getBean(String name) throws BeansException {

return doGetBean(name, null, null, false);

}

@Override

public T getBean(String name, @Nullable Class requiredType) throws BeansException {

return doGetBean(name, requiredType, null, false);

}

@Override

public Object getBean(String name, Object... args) throws BeansException {

return doGetBean(name, null, args, false);

}

如果spring容器沒有創建好名稱為name的bean，就會先去調用下述方法去創建這個bean

AbstractAutowireCapableBeanFactory.createBean()

創建bean的過程中會先通過下述方法進行屬性填充

populateBean(beanName, mbd, instanceWrapper)

填充完成以後，接著去調用下述方法初始化bean

AbstractAutowireCapableBeanFactory.initializeBean(beanName, exposedObject, mbd)

初始化bean的過程就是bean的生命週期執行過程，而後置處理器BeanPostProcessor的postProcessBeforeInitialization和postProcessAfterInitialization方法調用就在此過程中完成

protected Object initializeBean(final String beanName, final Object bean, @Nullable RootBeanDefinition mbd) {

//省略部分代碼...

//調用Aware接口的setXXX方法

invokeAwareMethods(beanName, bean);

Object wrappedBean = bean;

if (mbd == null || !mbd.isSynthetic()) {

//調用BeanPostProcessor接口的BeanPostProcessorsBeforeInitialization方法

wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);

}

try {

//調用自定義的init-method方法

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()) {

//調用BeanPostProcessor接口的postProcessAfterInitialization方法

wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);

}

return wrappedBean;

}

執行invokeAwareMethods時，會判斷當前bean是否實現XXXAware接口，如果實現了XXXAware接口，則會去調用setXXX方法

private void invokeAwareMethods(final String beanName, final Object bean) {

if (bean instanceof Aware) {

if (bean instanceof BeanNameAware) {

((BeanNameAware) bean).setBeanName(beanName);

}

if (bean instanceof BeanClassLoaderAware) {

ClassLoader bcl = getBeanClassLoader();

if (bcl != null) {

((BeanClassLoaderAware) bean).setBeanClassLoader(bcl);

}

}

if (bean instanceof BeanFactoryAware) {

((BeanFactoryAware) bean).setBeanFactory(AbstractAutowireCapableBeanFactory.this);

}

}

}

執行applyBeanPostProcessorsBeforeInitialization方法，會遍歷Spring容器中所有的後置處理器，而且會調用每個後置處理器的postProcessBeforeInitialization方法

@Override

public Object applyBeanPostProcessorsBeforeInitialization(Object existingBean, String beanName) throws BeansException {

Object result = existingBean;

for (BeanPostProcessor beanProcessor : getBeanPostProcessors()) {

Object current = beanProcessor.postProcessBeforeInitialization(result, beanName);

if (current == null) {

return result;

}

result = current;

}

return result;

}

執行invokeInitMethods方法，會先判斷當前的bean有沒有實現InitializingBean接口，如果實現了，則會調用InitializingBean接口的afterPropertiesSet()方法，然後判斷是否自定義了init-method，如果有，則會執行其init-method

protected void invokeInitMethods(String beanName, final Object bean, @Nullable RootBeanDefinition mbd) throws Throwable {

//省略部分代碼

//調用afterPropertiesSet方法

((InitializingBean) bean).afterPropertiesSet();

//判斷如果自定義了init-method，就會執行init-method

if (mbd != null && bean.getClass() != NullBean.class) {

String initMethodName = mbd.getInitMethodName();

if (StringUtils.hasLength(initMethodName) &&

!(isInitializingBean && "afterPropertiesSet".equals(initMethodName)) &&

!mbd.isExternallyManagedInitMethod(initMethodName)) {

invokeCustomInitMethod(beanName, bean, mbd);

}

}

}

最後執行applyBeanPostProcessorsAfterInitialization方法，會遍歷Spring容器中所有的後置處理器，而且會調用每個後置處理器的postProcessAfterInitialization方法

@Override

public Object applyBeanPostProcessorsAfterInitialization(Object existingBean, String beanName)

throws BeansException {

Object result = existingBean;

for (BeanPostProcessor beanProcessor : getBeanPostProcessors()) {

Object current = beanProcessor.postProcessAfterInitialization(result, beanName);

if (current == null) {

return result;

}

result = current;

}

return result;

}

通過bean的生命週期執行過程，就可瞭解BeanPostProcessor的整個調用過程

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關鍵字: 接口 後置 處理器

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