Spring

Bean的创建过程

Bean的创建实际上是由AbstractAutowireCapableBeanFactory的createBean方法内部实现的，

protected Object createBean(final String beanName, final RootBeanDefinition mbd, final Object[] args)
            throws BeanCreationException {
        AccessControlContext acc = AccessController.getContext();
        return AccessController.doPrivileged(new PrivilegedAction() {
            public Object run() {
                if (logger.isDebugEnabled()) {
                    logger.debug("Creating instance of bean '" + beanName + "'");
                }
                // Make sure bean class is actually resolved at this point.
                resolveBeanClass(mbd, beanName);
                // Prepare method overrides.
                try {
                    mbd.prepareMethodOverrides();
                }
                catch (BeanDefinitionValidationException ex) {
                    throw new BeanDefinitionStoreException(mbd.getResourceDescription(),
                            beanName, "Validation of method overrides failed", ex);
                }
                try {
                    // Give BeanPostProcessors a chance to return a proxy instead of the target bean instance.
                    Object bean = resolveBeforeInstantiation(beanName, mbd);
                    if (bean != null) {
                        return bean;
                    }
                }
                catch (Throwable ex) {
                    throw new BeanCreationException(mbd.getResourceDescription(), beanName,
                            "BeanPostProcessor before instantiation of bean failed", ex);
                }
                Object beanInstance = doCreateBean(beanName, mbd, args);
                if (logger.isDebugEnabled()) {
                    logger.debug("Finished creating instance of bean '" + beanName + "'");
                }
                return beanInstance;
            }
        }, acc);
    }

内部真正干活的是doCreateBean，里面包含了对于单例模式循环引用的处理，bean属性的设置和初始化的工作

rotected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final Object[] args) {
        // Instantiate the bean.
        BeanWrapper instanceWrapper = null;
        if (mbd.isSingleton()) {
            instanceWrapper = (BeanWrapper) 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);
            exposedObject = initializeBean(beanName, exposedObject, mbd);
        }
        catch (Throwable ex) {
            if (ex instanceof BeanCreationException && beanName.equals(((BeanCreationException) ex).getBeanName())) {
                throw (BeanCreationException) ex;
            }
            else {
                throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Initialization of bean failed", ex);
            }
        }
        if (earlySingletonExposure) {
            Object earlySingletonReference = getSingleton(beanName, false);
            if (earlySingletonReference != null) {
                if (exposedObject == bean) {
                    exposedObject = earlySingletonReference;
                }
                else if (!this.allowRawInjectionDespiteWrapping && hasDependentBean(beanName)) {
                    String[] dependentBeans = getDependentBeans(beanName);
                    Set actualDependentBeans = new LinkedHashSet(dependentBeans.length);
                    for (int i = 0; i < dependentBeans.length; i++) {
                        String dependentBean = dependentBeans[i];
                        if (!removeSingletonIfCreatedForTypeCheckOnly(dependentBean)) {
                            actualDependentBeans.add(dependentBean);
                        }
                    }
                    if (!actualDependentBeans.isEmpty()) {
                        throw new BeanCurrentlyInCreationException(beanName,
                                "Bean with name '" + beanName + "' has been injected into other beans [" +
                                StringUtils.collectionToCommaDelimitedString(actualDependentBeans) +
                                "] in its raw version as part of a circular reference, but has eventually been " +
                                "wrapped. This means that said other beans do not use the final version of the " +
                                "bean. This is often the result of over-eager type matching - consider using " +
                                "'getBeanNamesOfType' with the 'allowEagerInit' flag turned off, for example.");
                    }
                }
            }
        }
        // Register bean as disposable.
        registerDisposableBeanIfNecessary(beanName, bean, mbd);
        return exposedObject;
    }

得到Bean的实例之后，接下来进行初始化Bean
（1）设置Bean的属性
（2）initializeBean，里面首先是各种Aware，然后是applyBeanPostProcessorsBeforeInitialization，然后是调用初始化方法，然后是applyBeanPostProcessorsAfterInitialization

protected Object initializeBean(String beanName, Object bean, RootBeanDefinition mbd) {
        if (bean instanceof BeanNameAware) {
            ((BeanNameAware) bean).setBeanName(beanName);
        }
        if (bean instanceof BeanClassLoaderAware) {
            ((BeanClassLoaderAware) bean).setBeanClassLoader(getBeanClassLoader());
        }
        if (bean instanceof BeanFactoryAware) {
            ((BeanFactoryAware) bean).setBeanFactory(this);
        }
        Object wrappedBean = bean;
        if (mbd == null || !mbd.isSynthetic()) {
            wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
        }
        try {
            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()) {
            wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
        }
        return wrappedBean;
    }