【Spring】Bean的LifeCycle(生命周期)

菜瓜：水稻，上次说Bean的LifeCycle，还没讲完

水稻：啥？说人话？

菜瓜：spring，bean，生命周期

水稻：哦哦，下次直接说人话。说正事，先从BeanFactory、ApplicationContext和FactoryBean开始说起吧

• 我们知道（你不一定知道）BeanFactory是Spring访问Bean容器的根接口，源码的注释： “The root interface for accessing a Spring bean container.”
• 而ApplicationContext继承自BeanFactory，也就是说它具有BeanFactory的属性和方法，并进一步完善（继承其他的接口）
• FactoryBean跟前两个关系就不怎么大了，它是spring提供给用户创建bean的口子，有一些bean创建过程复杂，或者依赖第三方包等（Mybatis-Spring中）,可交给用户自己创建

菜瓜：嗯。。陷入沉思。。（欲言又止）

水稻：讲理论不给代码就是耍流氓

• 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("实现FactoryBean接口的类自身被放在IOC一级缓存的容器里面，getObject的对象是在另一个缓存对象中");
      }
  
      @Override
      public CustomBean getObject() {
          return new CustomBean();
      }
  
      @Override
      public Class<?> getObjectType() {
          return CustomBean.class;
      }
  
      static class CustomBean {
          public CustomBean() {
              System.out.println("自定义bean");
          }
      }
  }
  
  测试方法
  @Test
  public void testTransa() {
      BeanFactory context = new AnnotationConfigApplicationContext(ComponentScanD.class);
      System.out.println("factoryBean : " + context.getBean("fb"));
      System.out.println("&factoryBean : " + context.getBean("&fb"));
  }
  
  测试结果

  实现FactoryBean接口的类自身被放在IOC一级缓存的容器里面，getObject的对象是在另一个缓存对象中
    自定义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则是包裹容器的上下文，丰富容器的功能（资源加载，事件驱动等）。FactoryBean也是Spring扩展性的提现

水稻：WC，你这个总结提到了精髓。就是扩展性：如果BeanFactory是核心思想，那么其他的上下文，后置处理器，还是Aware接口等等，都是为了实现扩展

菜瓜：铺垫说完了，开始生命周期呗

水稻：这次咱们反过来先看源码，再看实验，再总结

• BeanFactory源码注释 - 定义了实现的生命周期

•  * @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源码实现类

• 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接口
              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;
      }

• 实验代码

• 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无参构造 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");
      }
  }
  
  测试代码
      @Test
      public void testLifeCycle() {
          AbstractApplicationContext applicationContext = new AnnotationConfigApplicationContext(ComponentScanD.class);
          applicationContext.close();// 这里不关闭容器的话，注销bean的方法会看不到打印
      }
  
  测试结果

  BeanFactoryPostProcessor bean com.vip.qc.postprocessor.InitializingBeanT
    init无参构造 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：实现什么的不重要，接口才是爸爸呀，BeanFactory定义好了生命周期，下面的实现也只是实现罢了

水稻：哈哈，你说的对，一流的公司卖标准

菜瓜：这里怎么没看到循环依赖的处理啊

水稻：是的。这里的源码我只截取了bean初始化完成之后的接口调用。循环依赖的处理在它前面。来来来，继续刚

菜瓜：刚不了刚不了，你一下子搞这么多玩意给我看，我哪看得完

水稻：您歇着，下次您什么时候想了解我再给您说

总结

• BeanFactory已经定义了整个的生命周期，子类只是负责实现，demo演示也只是为了证实。我们更应该关注更上层的东西
• ApplicationContext是对容器更精细化的包装，提供了更完善的功能
• FactoryBean是Spring扩展性的提现，可供用户自己定义创建bean。扩展性提炼的很好