【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：。。。那你真的是很棒棒哦！。。。bean生命周期的话，从BeanFactory、ApplicationContext和FactoryBean开始说起

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扩展性的体现

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

posted @ 2020-06-17 18:02 渠成阅读(559) 评论(0) 编辑收藏举报

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