序言

上一篇文章介绍了ConversionService,顺着finishBeanFactoryInitialization主流程继续往下走，这篇文章介绍EmbeddedValueResolver。

源码

源码中关于EmbeddedValueResolver有说到，如果没有BeanPostProcessor则创建一个默认的内嵌的值解析器。那我们来看看在这之前是否在beanFacroty中设置过该值。

protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {// Initialize conversion service for this context.// 如果包含ConversionService，则赋值给conversionService变量if (beanFactory.containsBean(CONVERSION_SERVICE_BEAN_NAME) &&beanFactory.isTypeMatch(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class)) {beanFactory.setConversionService(beanFactory.getBean(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class));}// Register a default embedded value resolver if no bean post-processor// (such as a PropertyPlaceholderConfigurer bean) registered any before:// at this point, primarily for resolution in annotation attribute values.// 如果beanFactory之前没有注册嵌入值解析器，则注册默认的嵌入值解析器，主要用于注解属性值的解析if (!beanFactory.hasEmbeddedValueResolver()) {beanFactory.addEmbeddedValueResolver(strVal -> getEnvironment().resolvePlaceholders(strVal));}// Initialize LoadTimeWeaverAware beans early to allow for registering their transformers early.// 获取实现了LoadTimeWeaverAware的监听器，并初始化String[] weaverAwareNames = beanFactory.getBeanNamesForType(LoadTimeWeaverAware.class, false, false);for (String weaverAwareName : weaverAwareNames) {getBean(weaverAwareName);}// Stop using the temporary ClassLoader for type matching.// 将临时类加载器设置为nullbeanFactory.setTempClassLoader(null);// Allow for caching all bean definition metadata, not expecting further changes.// 将beanFactory冻结，因为即将要实例化Bean所以冻结BeanDefinition，不允许再添加beanDefinitionbeanFactory.freezeConfiguration();// Instantiate all remaining (non-lazy-init) singletons.// 实例化所有剩余的单例beanbeanFactory.preInstantiateSingletons();}

何时添加EmbeddedValueResolver

通过对embeddedValueResolvers属性添加操作调用往回推，可以看到这样的继承关系 PropertySourcesPlaceholderConfigurer
——》 PlaceholderConfigurerSupport——》 PropertyResourceConfigurer——》BeanFactoryPostProcessor

	@Overridepublic void addEmbeddedValueResolver(StringValueResolver valueResolver) {this.embeddedValueResolvers.add(valueResolver);}@Overridepublic boolean hasEmbeddedValueResolver() {return !this.embeddedValueResolvers.isEmpty();}

而我们之前介绍BeanFactoryPostProcessor时有提到过，如果类实现了BeanFactoryPostProcessor则一定会有postProcessBeanFactory()方法。

所以我们直接看 PropertySourcesPlaceholderConfigurer下的postProcessBeanFactory()。

@Overridepublic void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {// 省略部分代码。。。。processProperties(beanFactory, new PropertySourcesPropertyResolver(this.propertySources));this.appliedPropertySources = this.propertySources;}

protected void processProperties(ConfigurableListableBeanFactory beanFactoryToProcess,final ConfigurablePropertyResolver propertyResolver) throws BeansException {//省略部分代码doProcessProperties(beanFactoryToProcess, valueResolver);}

最终在doProcessProperties()中做了addEmbeddedValueResolver()的操作。

protected void doProcessProperties(ConfigurableListableBeanFactory beanFactoryToProcess,StringValueResolver valueResolver) {//省略部分代码// New in Spring 3.0: resolve placeholders in embedded values such as annotation attributes.beanFactoryToProcess.addEmbeddedValueResolver(valueResolver);}

处理完EmbeddedValueResolver后，BeanFacroty依然做了一些准备工作，包括将临时类加载器置空等。其中值得关注的是beanFactory.freezeConfiguration();
方法中设置了configurationFrozen 标志为 true ，并将当前BeanFacroty中的 beanDefinitionNames 赋值给 frozenBeanDefinitionNames ，当我初始化Bean时，我的Bean一定是不会变化的，所以要进行冻结操作。

@Overridepublic void freezeConfiguration() {this.configurationFrozen = true;this.frozenBeanDefinitionNames = StringUtils.toStringArray(this.beanDefinitionNames);}