Spring IOC容器的初始化過程

1.容器初始化過程

整個過程可以理解為容器的初始化過程。

容器的初始化是通過AbstractApplicationContext的refresh()實現的。

 2.Bean的創建過程

有兩個問題

1.bean的創建時機

bean是在什么時候被創建的，有哪些規則

2.bean的創建過程

bean是怎么創建的，會選擇哪個構造函數？依賴如何注入？InitializingBean的set方法什么時候被調用？實現ApplicationContextAware,BeanFactoryAware，BeanNameAware，這些接口的bean的set方法何時被調用？

問題1 Bean的創建時機

在finishBeanFactoryInitialization()中調用preInstantiateSingletons()會完成單例對象的創建

@Override
    public void preInstantiateSingletons() throws BeansException {
        if (this.logger.isDebugEnabled()) {
            this.logger.debug("Pre-instantiating singletons in " + this);
        }

        // Iterate over a copy to allow for init methods which in turn register new bean definitions.
        // While this may not be part of the regular factory bootstrap, it does otherwise work fine.
        List<String> beanNames = new ArrayList<>(this.beanDefinitionNames);

        // Trigger initialization of all non-lazy singleton beans...
        for (String beanName : beanNames) {
            RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
            if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
                if (isFactoryBean(beanName)) {
                    final FactoryBean<?> factory = (FactoryBean<?>) getBean(FACTORY_BEAN_PREFIX + beanName);
                    boolean isEagerInit;
                    if (System.getSecurityManager() != null && factory instanceof SmartFactoryBean) {
                        isEagerInit = AccessController.doPrivileged((PrivilegedAction<Boolean>) () ->
                                ((SmartFactoryBean<?>) factory).isEagerInit(),
                                getAccessControlContext());
                    }
                    else {
                        isEagerInit = (factory instanceof SmartFactoryBean &&
                                ((SmartFactoryBean<?>) factory).isEagerInit());
                    }
                    if (isEagerInit) {
                        getBean(beanName);
                    }
                }
                else {
                    getBean(beanName);
                }
            }
        }

        // Trigger post-initialization callback for all applicable beans...
        for (String beanName : beanNames) {
            Object singletonInstance = getSingleton(beanName);
            if (singletonInstance instanceof SmartInitializingSingleton) {
                final SmartInitializingSingleton smartSingleton = (SmartInitializingSingleton) singletonInstance;
                if (System.getSecurityManager() != null) {
                    AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
                        smartSingleton.afterSingletonsInstantiated();
                        return null;
                    }, getAccessControlContext());
                }
                else {
                    smartSingleton.afterSingletonsInstantiated();
                }
            }
        }
    }

問題2  bean的創建過程

對於bean的創建過程其實都是通過調用工廠的getBean方法來完成的，這里面將會完成對構造函數的選擇，依賴注入等。

無論預先創建還是延遲加載都是調用getBean實現，AbstactBeanFactory定義了getBean的過程。

getBean過程很復雜，將單獨拿一篇來講。