spring IOC初始化

参考：https://javadoop.com/post/spring-ioc#customizeBeanFactory

https://javadoop.com/blogimages/spring-context/1.png
https://javadoop.com/blogimages/spring-context/2.png

    public ClassPathXmlApplicationContext(String[] paths, Class<?> clazz, ApplicationContext parent)
            throws BeansException {

        super(parent);
        Assert.notNull(paths, "Path array must not be null");
        Assert.notNull(clazz, "Class argument must not be null");
        this.configResources = new Resource[paths.length];
        for (int i = 0; i < paths.length; i++) {
            this.configResources[i] = new ClassPathResource(paths[i], clazz);
        }
        refresh();
    }

1、 首先会初始化一个ApplicationContext，其实是一个BeanFactory，然后调用他的refresh（）方法进行初始化

@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();

            // Prepare the bean factory for use in this context.
            prepareBeanFactory(beanFactory);

            try {
                // Allows post-processing of the bean factory in context subclasses.
                postProcessBeanFactory(beanFactory);

                // Invoke factory processors registered as beans in the context.
                invokeBeanFactoryPostProcessors(beanFactory);

                // Register bean processors that intercept bean creation.
                registerBeanPostProcessors(beanFactory);

                // Initialize message source for this context.
                initMessageSource();

                // Initialize event multicaster for this context.
                initApplicationEventMulticaster();

                // Initialize other special beans in specific context subclasses.
                onRefresh();

                // Check for listener beans and register them.
                registerListeners();

                // Instantiate all remaining (non-lazy-init) singletons.
                finishBeanFactoryInitialization(beanFactory);

                // Last step: publish corresponding event.
                finishRefresh();
            }

            catch (BeansException ex) {
                if (logger.isWarnEnabled()) {
                    logger.warn("Exception encountered during context initialization - " +
                            "cancelling refresh attempt: " + ex);
                }

                // Destroy already created singletons to avoid dangling resources.
                destroyBeans();

                // Reset 'active' flag.
                cancelRefresh(ex);

                // Propagate exception to caller.
                throw ex;
            }

            finally {
                // Reset common introspection caches in Spring's core, since we
                // might not ever need metadata for singleton beans anymore...
                resetCommonCaches();
            }
        }
    }

2、 在refresh方法中会先来个锁，防止在refresh还没有结束的时候又去启动或者销毁容器。

    @Override
    protected final void refreshBeanFactory() throws BeansException {
        if (hasBeanFactory()) {
            destroyBeans();
            closeBeanFactory();
        }
        try {
            DefaultListableBeanFactory beanFactory = createBeanFactory();
            beanFactory.setSerializationId(getId());
            customizeBeanFactory(beanFactory);
            loadBeanDefinitions(beanFactory);
            synchronized (this.beanFactoryMonitor) {
                this.beanFactory = beanFactory;
            }
        }
        catch (IOException ex) {
            throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);
        }
    }

3、 之后解析配置文件里面的bean定义，将它包装成一个beandefination保存到beanfactory中，保存在defaultlistablebeanfactory的beandefinationmap中。这里说的 Bean 还没有初始化，只是配置信息都提取出来了。
4、之后注册一些回调，一些监听器，和一些钩子方法用来扩展

          // 初始化所有的 singleton beans
         //（lazy-init 的除外）
         finishBeanFactoryInitialization(beanFactory);

5、调用finishBeanFactoryInitaization实例化bean
先进行实例化，如果不存在方法覆写，那么就使用反射进行实例化，否则使用CGLIB。如果有需要覆盖或者动态替换的方法使用Cglib进行动态代理，如果没有需要动态改变的方法那就直接使用反射进行实例化。所谓的动态替换或覆盖的情况，就是使用了replace或者lookup的配置方法。这两个方法的作用就是在调用目标方法的时候，对调用过程进行拦截，调用实现增强功能的拦截器，返回原来实例的代理。

protected Object initializeBean(final String beanName, final Object bean, RootBeanDefinition mbd) {
   if (System.getSecurityManager() != null) {
      AccessController.doPrivileged(new PrivilegedAction<Object>() {
         @Override
         public Object run() {
            invokeAwareMethods(beanName, bean);
            return null;
         }
      }, getAccessControlContext());
   }
   else {
      // 如果 bean 实现了 BeanNameAware、BeanClassLoaderAware 或 BeanFactoryAware 接口，回调
      invokeAwareMethods(beanName, bean);
   }

   Object wrappedBean = bean;
   if (mbd == null || !mbd.isSynthetic()) {
      // BeanPostProcessor 的 postProcessBeforeInitialization 回调
      wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
   }

   try {
      // 处理 bean 中定义的 init-method，
      // 或者如果 bean 实现了 InitializingBean 接口，调用 afterPropertiesSet() 方法
      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 的 postProcessAfterInitialization 回调
      wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
   }
   return wrappedBean;
}

6、之后进行属性的注入，调用回调方法，初始化等等。就是bean生命周期的那几步。
先实例化，在注入属性
如果实现了beanNameAware，beanFactoryAware，ApplicationContextAware，进行回调。
如果实现了BeanPostProcessor接口，调用PostProcessorsBeforeInitialization方法。
如果bean中定义了init-method或者实现了InitializingBean 接口，调用afterPorpertiesSet方法。
然后再调用BeanPostProcessor 的 postProcessAfterInitialization 回调
之后bean就初始化完成了。可以用了。

销毁的话如果实现了DisposableBean接口，调用destroy方法。如果自定义了destory-method，也会被调用。