【Spring】Bean的LifeCycle(生命週期)

菜瓜：水稻，上次說Bean的LifeCycle，還沒講完

水稻：啥？說人話？

菜瓜：spring，bean，生命週期

水稻：哦哦，下次直接說人話。說正事，先從BeanFactory、ApplicationContext和FactoryBean開始說起吧

• 我們知道（你不一定知道）BeanFactory是Spring訪問Bean容器的根介面，原始碼的註釋： “The root interface for accessing a Spring bean container.”
• 而ApplicationContext繼承自BeanFactory，也就是說它具有BeanFactory的屬性和方法，並進一步完善（繼承其他的介面）
• FactoryBean跟前兩個關係就不怎麼大了，它是spring提供給使用者建立bean的口子，有一些bean建立過程複雜，或者依賴第三方包等（Mybatis-Spring中）,可交給使用者自己建立

菜瓜：嗯。。陷入沉思。。（欲言又止）

水稻：講理論不給程式碼就是耍流氓

• package com.vip.qc.postprocessor;
  
  import org.springframework.beans.factory.FactoryBean;
  import org.springframework.stereotype.Component;
  
  /**
   * @author QuCheng on 2020/6/15.
   */
  @Component("fb")
  public class FactoryBeanT implements FactoryBean<FactoryBeanT.CustomBean> {
  
      public FactoryBeanT() {
          System.out.println("實現FactoryBean介面的類自身被放在IOC一級快取的容器裡面，getObject的物件是在另一個快取物件中");
      }
  
      @Override
      public CustomBean getObject() {
          return new CustomBean();
      }
  
      @Override
      public Class<?> getObjectType() {
          return CustomBean.class;
      }
  
      static class CustomBean {
          public CustomBean() {
              System.out.println("自定義bean");
          }
      }
  }
  
  測試方法
  @Test
  public void testTransa() {
      BeanFactory context = new AnnotationConfigApplicationContext(ComponentScanD.class);
      System.out.println("factoryBean : " + context.getBean("fb"));
      System.out.println("&factoryBean : " + context.getBean("&fb"));
  }
  
  測試結果
  

    實現FactoryBean介面的類自身被放在IOC一級快取的容器裡面，getObject的物件是在另一個快取物件中
    自定義bean
    factoryBean : com.vip.qc.postprocessor.FactoryBeanT$CustomBean@214b199c
    &factoryBean : com.vip.qc.postprocessor.FactoryBeanT@20d3d15a

菜瓜：懂了，BeanFactory是Spring的核心--容器，ApplicationContext則是包裹容器的上下文，豐富容器的功能（資源載入，事件驅動等）。FactoryBean也是Spring擴充套件性的提現

水稻：WC，你這個總結提到了精髓。就是擴充套件性：如果BeanFactory是核心思想，那麼其他的上下文，後置處理器，還是Aware介面等等，都是為了實現擴充套件

菜瓜：鋪墊說完了，開始生命週期唄

水稻：這次我們們反過來先看原始碼，再看實驗，再總結

• BeanFactory原始碼註釋 - 定義了實現的生命週期

•  * @author Rod Johnson
   * @author Juergen Hoeller
   * @author Chris Beams
   * @since 13 April 2001
   * @see BeanNameAware#setBeanName
   * @see BeanClassLoaderAware#setBeanClassLoader
   * @see BeanFactoryAware#setBeanFactory
   * @see org.springframework.context.ResourceLoaderAware#setResourceLoader
   * @see org.springframework.context.ApplicationEventPublisherAware#setApplicationEventPublisher
   * @see org.springframework.context.MessageSourceAware#setMessageSource
   * @see org.springframework.context.ApplicationContextAware#setApplicationContext
   * @see org.springframework.web.context.ServletContextAware#setServletContext
   * @see org.springframework.beans.factory.config.BeanPostProcessor#postProcessBeforeInitialization
   * @see InitializingBean#afterPropertiesSet
   * @see org.springframework.beans.factory.support.RootBeanDefinition#getInitMethodName
   * @see org.springframework.beans.factory.config.BeanPostProcessor#postProcessAfterInitialization
   * @see DisposableBean#destroy
   * @see org.springframework.beans.factory.support.RootBeanDefinition#getDestroyMethodName
   */
  public interface BeanFactory {

• BeanFactory原始碼實現類

• public abstract class AbstractAutowireCapableBeanFactory extends AbstractBeanFactory implements AutowireCapableBeanFactory
  
  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 {
              // BeanNameAware BeanFactoryAware ...
              invokeAwareMethods(beanName, bean);
          }
  
          Object wrappedBean = bean;
          if (mbd == null || !mbd.isSynthetic()) {
              // BeanPostProcessor Before  @PostConstruct
              wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
          }
  
          try {
              // initMethod InitializingBean介面
              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()) {
              // BeanPostProcessor after
              wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
          }
  
          return wrappedBean;
      }

• 實驗程式碼

• package com.vip.qc.postprocessor;
  
  import org.springframework.beans.BeansException;
  import org.springframework.beans.factory.config.BeanDefinition;
  import org.springframework.beans.factory.config.BeanFactoryPostProcessor;
  import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
  import org.springframework.stereotype.Component;
  
  /**
   * @author QuCheng on 2020/6/14.
   */
  @Component
  public class BeanFactoryPostProcessorT implements BeanFactoryPostProcessor {
  
      public static final String BEAN_NAME = "initializingBeanT";
  
      @Override
      public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
          BeanDefinition initializingBeanT = beanFactory.getBeanDefinition(BEAN_NAME);
          System.out.println("BeanFactoryPostProcessor bean " + initializingBeanT.getBeanClassName());
      }
  }
  
  
  
  package com.vip.qc.postprocessor;
  
  import org.springframework.beans.BeansException;
  import org.springframework.beans.factory.config.BeanPostProcessor;
  import org.springframework.stereotype.Component;
  
  /**
   * @author QuCheng on 2020/6/14.
   */
  @Component
  public class BeanPostProcessorT implements BeanPostProcessor {
  
      public static final String BEAN_NAMET = "initializingBeanT";
  
      @Override
      public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
          if (BEAN_NAMET.equals(beanName)) {
              InitializingBeanT processorT = ((InitializingBeanT) bean);
              System.out.println("BeanPostProcessor BeforeInitialization " + processorT);
          }
          return bean;
      }
  
      @Override
      public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
          if (BEAN_NAMET.equals(beanName)){
              InitializingBeanT processorT = ((InitializingBeanT) bean);
              System.out.println("BeanPostProcessor AfterInitialization " + processorT);
          }
          return bean;
      }
  
  }
  
  
  package com.vip.qc.postprocessor;
  
  import org.springframework.beans.factory.BeanNameAware;
  import org.springframework.beans.factory.DisposableBean;
  import org.springframework.beans.factory.InitializingBean;
  import org.springframework.stereotype.Component;
  
  import javax.annotation.PostConstruct;
  import javax.annotation.PreDestroy;
  
  /**
   * @author QuCheng on 2020/6/14.
   */
  @Component
  public class InitializingBeanT implements BeanNameAware, InitializingBean, DisposableBean {
  
      public InitializingBeanT() {
          System.out.println("init無參構造 execute");
      }
  
      @PostConstruct
      public void postConstruct() {
          System.out.println("@PostConstruct  execute");
      }
  
      @PreDestroy
      public void preDestroy() {
          System.out.println("@PreDestroy  execute");
      }
  
      @Override
      public void afterPropertiesSet() {
          System.out.println("InitializingBean afterPropertiesSet --> " + this.toString());
      }
  
      @Override
      public void setBeanName(String name) {
          System.out.println("BeanNameAware : " + name);
      }
  
      @Override
      public void destroy() {
          System.out.println("destroy");
      }
  }
  
  
  測試程式碼
      @Test
      public void testLifeCycle() {
          AbstractApplicationContext applicationContext = new AnnotationConfigApplicationContext(ComponentScanD.class);
          applicationContext.close();// 這裡不關閉容器的話，登出bean的方法會看不到列印
      }
  
  測試結果
  

    BeanFactoryPostProcessor bean com.vip.qc.postprocessor.InitializingBeanT
    init無參構造 execute
    BeanNameAware : initializingBeanT
    BeanPostProcessor BeforeInitialization com.vip.qc.postprocessor.InitializingBeanT@15bb6bea
    @PostConstruct execute
    InitializingBean afterPropertiesSet --> com.vip.qc.postprocessor.InitializingBeanT@15bb6bea
    BeanPostProcessor AfterInitialization com.vip.qc.postprocessor.InitializingBeanT@15bb6bea
    @PreDestroy execute
    destroy

菜瓜：實現什麼的不重要，介面才是爸爸呀，BeanFactory定義好了生命週期，下面的實現也只是實現罷了

水稻：哈哈，你說的對，一流的公司賣標準

菜瓜：這裡怎麼沒看到迴圈依賴的處理啊

水稻：是的。這裡的原始碼我只擷取了bean初始化完成之後的介面呼叫。迴圈依賴的處理在它前面。來來來，繼續剛

菜瓜：剛不了剛不了，你一下子搞這麼多玩意給我看，我哪看得完

水稻：您歇著，下次您什麼時候想了解我再給您說

 

總結

• BeanFactory已經定義了整個的生命週期，子類只是負責實現，demo演示也只是為了證實。我們更應該關注更上層的東西 
• ApplicationContext是對容器更精細化的包裝，提供了更完善的功能
• FactoryBean是Spring擴充套件性的提現，可供使用者自己定義建立bean。擴充套件性提煉的很好