Constructor<?>[] ctors = determineConstructorsFromBeanPostProcessors(beanClass, beanName);
		if (ctors != null || mbd.getResolvedAutowireMode() == AUTOWIRE_CONSTRUCTOR ||
				mbd.hasConstructorArgumentValues() || !ObjectUtils.isEmpty(args)) {
			return autowireConstructor(beanName, mbd, ctors, args);//自动注入构造器参数
		}

上面这串代码是在AbstractAutowireCapableBeanFactory类中的createBeanInstance方法中。

	@Nullable
	protected Constructor<?>[] determineConstructorsFromBeanPostProcessors(@Nullable Class<?> beanClass, String beanName)
			throws BeansException {

		if (beanClass != null && hasInstantiationAwareBeanPostProcessors()) {
			for (SmartInstantiationAwareBeanPostProcessor bp : getBeanPostProcessorCache().smartInstantiationAware) {
				Constructor<?>[] ctors = bp.determineCandidateConstructors(beanClass, beanName);
				if (ctors != null) {
					return ctors;
				}
			}
		}
		return null;
	}

determineConstructorsFromBeanPostProcessors是决定用哪个构造器，也可以自己实现用选择用哪个构造器