Spring ioc容器是什么时候创建的

缘起

一直说Spring ioc容器，但是它是什么时候创建的呢? 且听我慢慢道来.

分析

debug用的demo是【1】.

首先进到我们的老朋友——refresh方法中去

org.springframework.context.support.AbstractApplicationContext.refresh()

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@Override
	public void refresh() throws BeansException, IllegalStateException {
		synchronized (this.startupShutdownMonitor) {
			// Prepare this context for refreshing.
			prepareRefresh();

			// Tell the subclass to refresh the internal bean factory.
			ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
            ...

​ 源码1

注意第8行就获取了我们的ioc容器——beanFactory.

然后后面不论是进行我们熟知的 invokeBeanFactoryPostProcessors还是registerBeanPostProcessors还是finishBeanFactoryInitialization，都带上了它.

跟进源码1的第8行

org.springframework.context.support.AbstractApplicationContext.obtainFreshBeanFactory()

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protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
		refreshBeanFactory();
		ConfigurableListableBeanFactory beanFactory = getBeanFactory();
		if (logger.isDebugEnabled()) {
			logger.debug("Bean factory for " + getDisplayName() + ": " + beanFactory);
		}
		return beanFactory;
	}

​ 源码2

跟进源码2的第2行

org.springframework.context.support.GenericApplicationContext.refreshBeanFactory()

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@Override
	protected final void refreshBeanFactory() throws IllegalStateException {
		if (!this.refreshed.compareAndSet(false, true)) {
			throw new IllegalStateException(
					"GenericApplicationContext does not support multiple refresh attempts: just call 'refresh' once");
		}
		this.beanFactory.setSerializationId(getId());
	}

​ 源码3

而beanFactory是作为GenericApplicationContext的属性的. 但是AnnotationConfigApplicationContext是GenericApplicationContext的子类，所以父类的构造器也会被执行. 看看GenericApplicationContext的构造器

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public GenericApplicationContext() {
		this.beanFactory = new DefaultListableBeanFactory();
	}

是直接new出来的. 也就是说我们在main方法中写下

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ApplicationContext applicationContext = new AnnotationConfigApplicationContext(MainConfig.class);

的时候，就已经初始化AnnotationConfigApplicationContext的父类GenericApplicationContext，而在GenericApplicationContext 中就初始化了beanFactory，亦即ioc容器.

所以我们就明白了Spring IOC 容器是什么时候产生的了.

DEMO

【1】https://github.com/yfsyfs/backend/tree/master/spring-annotation-condition