Spring Bean生命周期详解和应用（中）

我就是我 2024-03-23 15:40 75阅读 0赞

## 生命周期详解 ##

![format_png][]

Bean的完整生命周期经历各种方法调用，这些方法可以划分为以下几类：（结合上图，需要有如下顶层思维）

*  Bean自身的方法：包括了Bean本身调用的方法和通过配置文件中`<bean>`的init-method和destroy-method指定的方法。
 *  Bean级生命周期接口方法：包括了BeanNameAware、BeanFactoryAware、ApplicationContextAware；当然也包括InitializingBean和DiposableBean接口的方法（可以被@PostConstruct和@PreDestory注解替代）
 *  容器级生命周期接口方法：包括了InstantionAwareBeanProcessor和BeanPostProcessor。
 *  工厂后处理器接口方法：包括了AspectJWwavingEnabler，ConfigurationClassPostProcessor,CustomAutowireConfigurer等非常有用的工厂后处理接口的方法，工厂后处理器也是容器级的。在应用上下文装配配置文件之后立即调用。

### 结合源码 ###

![format_png 1][]

入口当然是AbstractApplication\#refresh，下面我们来看看整个过程，部分源码在时序图中已经贴出，详细源码可以调试查看。

1.  执行AbstractApplication\#invokeBeanFactoryPostProcessors：调用所有beanFactory的postProcessors。
2.  执行PostProcessorRegisrtrationDelegate：执行所有注册BeanFactoryPostProcessors

String[] postProcessorNames =
    
    beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false);
    
    ...
    
    invokeBeanFactoryPostProcessors(nonOrderedPostProcessors, beanFactory);  
    
    
    ...
    
    for (BeanFactoryPostProcessor postProcessor : postProcessors) {
    
    postProcessor.postProcessBeanFactory(beanFactory);
    
    }
    复制代码

3. 执行MyBeanFactoryPostProcessor\#postProcessBeanFactory：在Bean被实例化之前，允许被覆盖或添加属性。

@Override  
    public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {  
    log.info("调用BeanFactoryPostProcessor#postProcessBeanFactory");  
    BeanDefinition bd = beanFactory.getBeanDefinition("person");  
    bd.getPropertyValues().addPropertyValue("phone", "110");  
    }
    复制代码

4. 执行所有AbstractApplicationContext\#finishBeanFactoryInitialization：实例化素有剩余的单例。 5. 执行**AbstractAutowireCapableBeanFactory**\#createBean：

@Override
    	protected Object createBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args)
    			throws BeanCreationException {
                 ...           
                // Give BeanPostProcessors a chance to return a proxy instead of the target bean instance.  
                Object bean = resolveBeforeInstantiation(beanName, mbdToUse);
                ...
                Object beanInstance = doCreateBean(beanName, mbdToUse, args);
                ...
         }       
    复制代码

6. 执行**AbstractAutowireCapableBeanFactory**\#resolveBeforeInstantiation：

@Nullable
    protected Object resolveBeforeInstantiation(String beanName, RootBeanDefinition mbd) {
       Object bean = null;
       // 可以看到BeanDefinition记录了生命周期的一些信息
       if (!Boolean.FALSE.equals(mbd.beforeInstantiationResolved)) {
          // Make sure bean class is actually resolved at this point.
          if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
             Class<?> targetType = determineTargetType(beanName, mbd);
             if (targetType != null) {
                bean = applyBeanPostProcessorsBeforeInstantiation(targetType, beanName);
                // 可以发现postBeforeInstantuation可以抑制返回代理bean，有效抑制bean进行实例化，直接执行AfterIntialization。
                if (bean != null) {
                   bean = applyBeanPostProcessorsAfterInitialization(bean, beanName);
                }
             }
          }
          mbd.beforeInstantiationResolved = (bean != null);
       }
       return bean;
    }
    复制代码

7. 调用**AbstractAutowireCapableBeanFactory**\#applyBeanPostProcessorsBeforeInstantiation：

@Nullable  
    protected Object applyBeanPostProcessorsBeforeInstantiation(Class beanClass, String beanName) {  
    for (BeanPostProcessor bp : getBeanPostProcessors()) {  
    if (bp instanceof InstantiationAwareBeanPostProcessor) {  
    InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;  
    Object result = ibp.postProcessBeforeInstantiation(beanClass, beanName);  
    if (result != null) {  
    return result;  
    }  
    }  
    }  
    return null;  
    }  
    复制代码

责任链的方式调用所有该bean的postProcessBeforeInstanttiation

1.  调用MyInstantiationAwareBeanPostProcessor\#postProcessBeforeInstantiation：

@Override
    public Object postProcessBeforeInstantiation(Class<?> beanClass, String beanName) throws BeansException {
        log.info("InstantiationAwareBeanPostProcessorAdapter调用postProcessBeforeInstantiation方法，beanClass:{},beanName:{}", beanClass.getName(), beanName);
        return super.postProcessBeforeInstantiation(beanClass, beanName);
    }
    复制代码

在实例化目标在bean之前执行，如果返回不为null那返回的就是代理bean，可以有效的抑制target bean的默认实例化。

1.  执行**AbstractAutowireCapableBeanFactory**\#doCreateBean：返回createBean方法继续执行doCreateBean。
2.  执行**AbstractAutowireCapableBeanFactory**\#createBeanInstance
3.  执行**AbstractAutowireCapableBeanFactory**\#insatntiateBean：使用无参构造器进行实例化。
4.  执行Person构造器进行实例化。
5.  执行**AbstractAutowireCapableBeanFactory**\#populateBean：

protected void populateBean(String beanName, RootBeanDefinition mbd, @Nullable BeanWrapper bw) {
    ...
       // Give any InstantiationAwareBeanPostProcessors the opportunity to modify the
       // state of the bean before properties are set. This can be used, for example,
       // to support styles of field injection.
       if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
          for (BeanPostProcessor bp : getBeanPostProcessors()) {
             if (bp instanceof InstantiationAwareBeanPostProcessor) {
                InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
                // 执行InstantiationAwareBeanPostProcessor#postProcessAfterInstantion
                if (!ibp.postProcessAfterInstantiation(bw.getWrappedInstance(), beanName)) {
                   return;
                }
             }
          }
       }
    
    ...
       if (hasInstAwareBpps) {
          if (pvs == null) {
             pvs = mbd.getPropertyValues();
          }
          for (BeanPostProcessor bp : getBeanPostProcessors()) {
             if (bp instanceof InstantiationAwareBeanPostProcessor) {
                InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
                // 执行InsantiationAwareBeanPostProcess#postProcessProperties
                PropertyValues pvsToUse = ibp.postProcessProperties(pvs, bw.getWrappedInstance(), beanName);
                if (pvsToUse == null) {
                   if (filteredPds == null) {
                      filteredPds = filterPropertyDescriptorsForDependencyCheck(bw, mbd.allowCaching);
                   }
                   //填充属性值
                   pvsToUse = ibp.postProcessPropertyValues(pvs, filteredPds, bw.getWrappedInstance(), beanName);
                   if (pvsToUse == null) {
                      return;
                   }
                }
                pvs = pvsToUse;
             }
          }
       }
       if (needsDepCheck) {
          if (filteredPds == null) {
             filteredPds = filterPropertyDescriptorsForDependencyCheck(bw, mbd.allowCaching);
          }
          checkDependencies(beanName, mbd, filteredPds, pvs);
       }
    
       if (pvs != null) {
          applyPropertyValues(beanName, mbd, bw, pvs);
       }
    }
    复制代码

14. 执行MyInstantiationAwareBeanPostProcessor\#postProcessAfterInstantiation：

@Override
    public boolean postProcessAfterInstantiation(Object bean, String beanName) throws BeansException {
        log.info("InstantiationAwareBeanPostProcessorAdapter调用postProcessAfterInstantiation方法，bean:{},beanName:{}", bean, beanName);
        return super.postProcessAfterInstantiation(bean, beanName);
    }
    复制代码

在bean被实例化后，在Spring属性填充之前，执行自定义字段注入。如果返回true属性正常填充，返回false跳过属性填充还将阻止在bean实例在调用任何后续的InstantiationAwareBeanPostProcessor实例。

1.  执行MyInstantiationAwareBeanPostProcessor\#postProcessProperties：

@Override
    public PropertyValues postProcessProperties(PropertyValues pvs, Object bean, String beanName) throws BeansException {
        log.info("InstantiationAwareBeanPostProcessorAdapter调用postProcessProperties方法,pvs:{}", JSON.toJSONString(pvs.getPropertyValues()));
        return super.postProcessProperties(pvs, bean, beanName);
    }
    复制代码

在工厂将给定的属性应用于给定的bean之前对其进行后处理。

1.  返回AbstractAutowireCapableBeanFactory\#populateBean调用applyPropertyValues填充属性，执行Person的set方法。
2.  继续**AbstractAutowireCapableBeanFactory**\#doCreateBean往下执行**AbstractAutowireCapableBeanFactory**\#initializeBean：

protected Object initializeBean(final String beanName, final Object bean, @Nullable RootBeanDefinition mbd) {
       if (System.getSecurityManager() != null) {
          AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
             invokeAwareMethods(beanName, bean);
             return null;
          }, getAccessControlContext());
       }
       else {
           //执行各种Aware如BeanFactoryAware、BeanNameAware
          invokeAwareMethods(beanName, bean);
       }
    
       Object wrappedBean = bean;
       if (mbd == null || !mbd.isSynthetic()) {
          //执行BeanPostProcessor#postProcessBeforeInitialization、InstantiationAwareBeanPostProcessor#postProcessBeforeInitialization、@PostConstruct注释的方法
          wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
       }
    
       try {
          //执行IntializingBean#afterPropertiesSet、init-method指定的方法
          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()) {
          wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
       }
    
       return wrappedBean;
    }
    复制代码

初始化给定的bean实例，应用工厂回调以及init方法和bean后处理器。  
18. 执行**AbstractAutowireCapableBeanFactory**\#invokeAwareMethods：

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);
          }
       }
    }
    复制代码

执行各种Aware

1.  执行Person\#setBeanName调用创建的bean设置在bean工厂中的bean name，Person\#setBeanFactory将拥有的工厂提供给bean实例的回调。
2.  执行**AbstractAutowireCapableBeanFactory**\#applyBeanPostProcessorsBeforeIntialization：

@Override
        public Object applyBeanPostProcessorsBeforeInitialization(Object existingBean, String beanName)
        throws BeansException {
    
            Object result = existingBean;
            for (BeanPostProcessor processor : getBeanPostProcessors()) {
            	Object current = processor.postProcessBeforeInitialization(result, beanName);
            	if (current == null) {
            		return result;
            	}
            	result = current;
            }
            return result;
    
        }
    复制代码

![format_png 2][]

可以看到我们自定义的两个BeanPostProcessor。其中@PostContruct是属于CommonAnnotationBeanPostProcessor，但是顺序靠后因此后执行，但都属于BeanPostProcessor。

1.  执行MyBeanFactoryPostProcessor/MyInsatantiationAwareBeanPostProcessor\#postProcessorBeforeInitialization：在bean初始化之前，可能是个代理的bean

@Override
    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        log.info("BeanPostProcessor接口调用postProcessBeforeInitialization");
        return BeanPostProcessor.super.postProcessBeforeInitialization(bean, beanName);
    }
    复制代码

22. 返回**AbstractAutowireCapableBeanFactory**\#applyBeanPostProcessorsBeforeIntialization执行Person被注释的@PostConstruct：此时bean依赖注入已经完成，可以使用该注解注释方法进行任何初始化

1.  返回**AbstractAutowireCapableBeanFactory**\#initializeBean执行invokeInitMethods执行Person\#afterPropertiesSet：此时bean依赖注入已经完成，可以使用该注解注释方法进行任何初始化。
2.  返回**AbstractAutowireCapableBeanFactory**\#invokeInitMethods执行Person\#myInit、Person实现的InitializingBean\#afterPropertiesSet方法。
3.  返回**AbstractAutowireCapableBeanFactory**\#applyBeanPostPostProcessorAfterInitialization执行MyBeanFactoryPostProcessor/MyInstantiationAwareBeanPostProcessor\#PostProcessAfterInitialization：

@Override
    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        log.info("BeanPostProcessor接口调用postProcessAfterInitialization");
        return BeanPostProcessor.super.postProcessAfterInitialization(bean, beanName);
    }
    复制代码

@Override
    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        log.info("InstantiationAwareBeanPostProcessorAdapter调用postProcessAfterInitialization");
        return super.postProcessAfterInitialization(bean, beanName);
    }
    复制代码

在实例化后由BeanFactory或者BeanFactory创建的对象调用，自此会退出AbstractAutowireCapableBeanFactory\#initializeBean方法。

1.  执行AbstractApplicationContext\#destroyBeans方法：

protected void destroyBeans() {
       getBeanFactory().destroySingletons();
    }
    复制代码

1.  执行DisposableBeanAdapter\#destroy：

public void destroy() {  
    if (!CollectionUtils.isEmpty(this.beanPostProcessors)) {  
    for (DestructionAwareBeanPostProcessor processor : this.beanPostProcessors) {  
    //执行@PreDestroy注释的方法  
    processor.postProcessBeforeDestruction(this.bean, this.beanName);  
    }  
    }  
      
    if (this.invokeDisposableBean) {  
    if (logger.isTraceEnabled()) {  
    logger.trace("Invoking destroy() on bean with name '" + this.beanName + "'");  
    }  
    try {  
    if (System.getSecurityManager() != null) {  
    AccessController.doPrivileged((PrivilegedExceptionAction) () -> {  
    ((DisposableBean) this.bean).destroy();  
    return null;  
    }, this.acc);  
    }  
    else {  
    // 执行DisposableBean#destroy方法  
    ((DisposableBean) this.bean).destroy();  
    }  
    }  
    catch (Throwable ex) {  
    String msg = "Invocation of destroy method failed on bean with name '" + this.beanName + "'";  
    if (logger.isDebugEnabled()) {  
    logger.warn(msg, ex);  
    }  
    else {  
    logger.warn(msg + ": " + ex);  
    }  
    }  
    }  
      
    if (this.destroyMethod != null) {  
    //执行Person destory-method方法  
    invokeCustomDestroyMethod(this.destroyMethod);  
    }  
    else if (this.destroyMethodName != null) {  
    Method methodToInvoke = determineDestroyMethod(this.destroyMethodName);  
    if (methodToInvoke != null) {  
    invokeCustomDestroyMethod(ClassUtils.getInterfaceMethodIfPossible(methodToInvoke));  
    }  
    }  
    }
    复制代码

贴出的代码注释了@PreDestory注释的方法、DisposableBean\#destroy、destory-method指定的方法执行的位置。

#### 总结 ####

通过源码来“具象化”来了解生命周期是怎么实现的，AbstractApplicationContext作为容器的总入口来发起对单例的实例化，AbstractAutowireCapableFactory顾名思义用于负责bean的创建、填充属性、初始化以及中间的各种“勾子”是bean生命周期的核心。

通过源码也解惑了很多，比如执行顺序：@PostConstruct为啥比InitializingBean\#afterPropetiesSet、init-method先执行，后续我们将继续了解下如何应用提供的这些“勾子”对生命周期进一步了解。

[format_png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/23/73544caf080f4f1f849eec20e5a2afc6.png
[format_png 1]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/23/1c60cb24e55d41f2b13dab0f74493844.png
[format_png 2]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/23/ad94bf2bb00c46c496c7b25004dd5f59.png