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Spring启动过程中实例化前部分的分析

发布时间:2022/9/13 13:31:24

 

代码部分

  说明

    1.hasInstantiationAwareBeanPostProcessors()方法说明

        其实是判断  AbstractBeanFactory类的hasInstantiationAwareBeanPostProcessors中  是否标志有处理器( 5.3版本后其实是存放于BeanPostProcessorCache中,里面有四个List都是用于存放各种处理器的缓存,不用多做在意,因为5.3之后都是一次性全部遍历存完,优化了部分)

     2.applyBeanPostProcessorsBeforeInstantiation(Class<?> beanClass, String beanName) 方法说明

           该方法作用有两种,一种是修改对象实例元数据(因为还没被创建,所以元数据的改动会导致实例的改动)一种是提前返回Bean对象(可以返回自己定义的某个对象实例)

     3.applyBeanPostProcessorsAfterInitialization(Object existingBean, String beanName) 方法说明

           该方法为初始化后的调用方法,为什么如果bean创建后要调用呢?  因为这个方法与AOP有关,在这个方法中进行AOP,是每个bean都要进行处理的方法,在这个方法内判断需不需要进行动态代理,不需要就返回本身,需要就进行动态代理。(具体可查看  Spring的AOP底层解析  )

  代码展示

protected Object resolveBeforeInstantiation(String beanName, RootBeanDefinition mbd) {
    Object bean = null;
    if (!Boolean.FALSE.equals(mbd.beforeInstantiationResolved)) {
        if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
            Class<?> targetType = determineTargetType(beanName, mbd);
            if (targetType != null) {
                bean = applyBeanPostProcessorsBeforeInstantiation(targetType, beanName);
                if (bean != null) {
                    bean = applyBeanPostProcessorsAfterInitialization(bean, beanName);
                }
            }
        }
        mbd.beforeInstantiationResolved = (bean != null);
    }
    return bean;
}

   

  版本区别的记录展示

    applyBeanPostProcessorsBeforeInstantiation方法的差异(applyBeanPostProcessorsAfterInitialization方法类似,就写出来了

      说明

        1.改进后的版本明显会比之前版本要快,而且会简化一点,因为BeanPostProcessor的全部遍历只会进行一次,而不是每个Bean都会全部遍历一次。(这里面涉及到策略设计模式,本质上取决于,如果bean被创建出来了,后面的处理器其实就不会被调用

        2.以空间换时间的思维更加明显,相比于名称都要拿出全部的BeanPostProcessor进行遍历(而且某些类型还不是需要的),不如按照类型进行划分缓存,虽说消耗了一定量的空间,但是能更快速的按照类型拿出需要的BeanPostProcessor进行遍历处理

      代码展示

//5.3之前的版本
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;
}

//5.3之后的版本
static class BeanPostProcessorCache {
    final List<InstantiationAwareBeanPostProcessor> instantiationAware = new ArrayList<>();

    final List<SmartInstantiationAwareBeanPostProcessor> smartInstantiationAware = new ArrayList<>();

    final List<DestructionAwareBeanPostProcessor> destructionAware = new ArrayList<>();

    final List<MergedBeanDefinitionPostProcessor> mergedDefinition = new ArrayList<>();
}

BeanPostProcessorCache getBeanPostProcessorCache() {
    BeanPostProcessorCache bpCache = this.beanPostProcessorCache;
    if (bpCache == null) {
        bpCache = new BeanPostProcessorCache();
        for (BeanPostProcessor bp : this.beanPostProcessors) {
            if (bp instanceof InstantiationAwareBeanPostProcessor) {
                bpCache.instantiationAware.add((InstantiationAwareBeanPostProcessor) bp);
                if (bp instanceof SmartInstantiationAwareBeanPostProcessor) {
                    bpCache.smartInstantiationAware.add((SmartInstantiationAwareBeanPostProcessor) bp);
                }
            }
            if (bp instanceof DestructionAwareBeanPostProcessor) {
                bpCache.destructionAware.add((DestructionAwareBeanPostProcessor) bp);
            }
            if (bp instanceof MergedBeanDefinitionPostProcessor) {
                bpCache.mergedDefinition.add((MergedBeanDefinitionPostProcessor) bp);
            }
        }
        this.beanPostProcessorCache = bpCache;
    }
    return bpCache;
}

protected Object applyBeanPostProcessorsBeforeInstantiation(Class<?> beanClass, String beanName) {
    for (InstantiationAwareBeanPostProcessor bp : getBeanPostProcessorCache().instantiationAware) {
        Object result = bp.postProcessBeforeInstantiation(beanClass, beanName);
        if (result != null) {
            return result;
        }
    }
    return null;
}

 

applyBeanPostProcessorsAfterInitialization
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