【Spring】Bean的LifeCycle(生命週期)

渠成發表於2020-06-17
SpringBean

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

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