Spring是如何对bean进行初始化的。

简单来说在Spring的ApplicationContext被调用了refresh方法后，就会获取刷新后的BeanFactory，在刷新后就对将配置文件进行解析，生成BeanDefinition，并用其BeanName作为key,BeanDefinition为value,放入初始化好的DefaultListableBeanFactory的beanDefinitionMap中存放。BeanName作为添加其beanDefinitionNames属性的集合当中。

而这些都是从context.refresh方法开始的，其中的一段代码

finishBeanFactoryInitialization(beanFactory);

	/**
	 * Finish the initialization of this context's bean factory,
	 * initializing all remaining singleton beans.
	 */
	protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {
//....
		// Stop using the temporary ClassLoader for type matching.
		beanFactory.setTempClassLoader(null);

		// Allow for caching all bean definition metadata, not expecting further changes.
		beanFactory.freezeConfiguration();

		// Instantiate all remaining (non-lazy-init) singletons.
		beanFactory.preInstantiateSingletons();//实例化所有的非懒加载的单例
	}

	public void preInstantiateSingletons() throws BeansException {
		if (this.logger.isInfoEnabled()) {
			this.logger.info("Pre-instantiating singletons in " + this);
		}
		List<String> beanNames;
		synchronized (this.beanDefinitionMap) {
			// 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.
			beanNames = new ArrayList<String>(this.beanDefinitionNames);//将所有的beanName放入一个集合中，用来遍历
		}
		for (String beanName : beanNames) {//遍历所有的beanName
			RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);//g根据beanName获得BeanDefinition
			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(new PrivilegedAction<Boolean>() {
							public Boolean run() {
								return ((SmartFactoryBean<?>) factory).isEagerInit();
							}
						}, getAccessControlContext());
					}
					else {
						isEagerInit = (factory instanceof SmartFactoryBean &&
								((SmartFactoryBean<?>) factory).isEagerInit());
					}
					if (isEagerInit) {
						getBean(beanName);
					}
				}
				else {
					getBean(beanName);//根据BeanName获得Bean
				}
			}
		}
	}

	public Object getBean(String name) throws BeansException {
		return doGetBean(name, null, null, false);//根据BeanName获得Bean
	}

	protected <T> T doGetBean(
			final String name, final Class<T> requiredType, final Object[] args, boolean typeCheckOnly)
			throws BeansException {

		//....省略....
			try {
				final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);//获取BeanDefinition
				checkMergedBeanDefinition(mbd, beanName, args);

				// Guarantee initialization of beans that the current bean depends on.
				String[] dependsOn = mbd.getDependsOn();
				if (dependsOn != null) {
					for (String dependsOnBean : dependsOn) {
						getBean(dependsOnBean);
						registerDependentBean(dependsOnBean, beanName);
					}
				}

				// Create bean instance.创建Bean实例，需要进行判断，我们只看默认的单例
				if (mbd.isSingleton()) {
					sharedInstance = getSingleton(beanName, new ObjectFactory<Object>() {
						public Object getObject() throws BeansException {
							try {
								return createBean(beanName, mbd, args);
							}
							catch (BeansException ex) {
								// Explicitly remove instance from singleton cache: It might have been put there
								// eagerly by the creation process, to allow for circular reference resolution.
								// Also remove any beans that received a temporary reference to the bean.
								destroySingleton(beanName);
								throw ex;
							}
						}
					});
					bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
				}
                //....
				}
			}
//...
		}

//...
		return (T) bean;
	}

	protected Object createBean(final String beanName, final RootBeanDefinition mbd, final Object[] args)
			throws BeanCreationException {
//...

		Object beanInstance = doCreateBean(beanName, mbd, args);
		if (logger.isDebugEnabled()) {
			logger.debug("Finished creating instance of bean '" + beanName + "'");
		}
		return beanInstance;
	}

	protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final Object[] args) {
		// Instantiate the bean.
		BeanWrapper instanceWrapper = null;
		if (mbd.isSingleton()) {
			instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
		}
		if (instanceWrapper == null) {
			instanceWrapper = createBeanInstance(beanName, mbd, args);
		}
		final Object bean = (instanceWrapper != null ? instanceWrapper.getWrappedInstance() : null);
		Class<?> beanType = (instanceWrapper != null ? instanceWrapper.getWrappedClass() : null);

		// Allow post-processors to modify the merged bean definition.
		synchronized (mbd.postProcessingLock) {
			if (!mbd.postProcessed) {
				applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName);
				mbd.postProcessed = true;
			}
		}

		// Eagerly cache singletons to be able to resolve circular references
		// even when triggered by lifecycle interfaces like BeanFactoryAware.
		boolean earlySingletonExposure = (mbd.isSingleton() && this.allowCircularReferences &&
				isSingletonCurrentlyInCreation(beanName));
		if (earlySingletonExposure) {
			if (logger.isDebugEnabled()) {
				logger.debug("Eagerly caching bean '" + beanName +
						"' to allow for resolving potential circular references");
			}
			addSingletonFactory(beanName, new ObjectFactory() {
				public Object getObject() throws BeansException {
					return getEarlyBeanReference(beanName, mbd, bean);
				}
			});
		}

		// Initialize the bean instance.
		Object exposedObject = bean;
		try {
			populateBean(beanName, mbd, instanceWrapper);
			if (exposedObject != null) {
				exposedObject = initializeBean(beanName, exposedObject, mbd);
			}
		}
//..

		return exposedObject;
	}

单例的bean实例化后会存入DefaultListableFactoryBean的singletonObjects属性中，它是个Map.

太多了。。。。。不写了。。