Spring源码分析-白红宇

其他更多java基础文章：

Spring源码太大了，对于一个技术不深的我来说，第一次啃会很艰难，于是我决定一个模块一个模块的看，并且将在学习的过程中，觉得很不错的文章记录下来。建议大家先阅读推荐博客，然后再看我的补充。当前Spring版本4.3.18

Spring读取自定义xml文件解析

ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");复制代码

重点

整个容器的启动流程，都在AbstractApplicationContext的refresh()的模板方法中了

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();			}		}	}复制代码

下面讲解的重点是obtainFreshBeanFactory()这个方法。

总结

时序图我花时间重新画了一幅，但是流程太长，整条流程保存的画质不怎么好。所以我把整体和局部时序图都画出来，方便大家对比

下面是整个时序图的流转过程文字文字补充：

SpringMain->ClassPathXmlApplicationContext: new ClassPathXmlApplicationContext("applicationContext.xml");ClassPathXmlApplicationContext->AbstractRefreshableConfigApplicationContext: setConfigLocations()AbstractRefreshableConfigApplicationContext->ClassPathXmlApplicationContext: returnClassPathXmlApplicationContext->AbstractApplicationContext: refresh()AbstractApplicationContext->AbstractApplicationContext: obtainFreshBeanFactory()AbstractApplicationContext->AbstractRefreshableApplicationContext: refreshBeanFactory()AbstractRefreshableApplicationContext->AbstractXmlApplicationContext: loadBeanDefinitions()AbstractXmlApplicationContext->AbstractXmlApplicationContext: loadBeanDefinitions()AbstractXmlApplicationContext->AbstractBeanDefinitionReader: reader.loadBeanDefinitions(configLocations);AbstractBeanDefinitionReader->AbstractBeanDefinitionReader: counter += loadBeanDefinitions(location);AbstractBeanDefinitionReader->AbstractBeanDefinitionReader: return loadBeanDefinitions(location, null);AbstractBeanDefinitionReader->XmlBeanDefinitionReader: int loadCount = loadBeanDefinitions(resource);XmlBeanDefinitionReader->XmlBeanDefinitionReader: doLoadBeanDefinitions()XmlBeanDefinitionReader->XmlBeanDefinitionReader: registerBeanDefinitions()XmlBeanDefinitionReader->DefaultBeanDefinitionDocumentReader: registerBeanDefinitions(doc, createReaderContext(resource));DefaultBeanDefinitionDocumentReader->DefaultBeanDefinitionDocumentReader: doRegisterBeanDefinitions()DefaultBeanDefinitionDocumentReader->DefaultBeanDefinitionDocumentReader: parseBeanDefinitions()DefaultBeanDefinitionDocumentReader->DefaultBeanDefinitionDocumentReader: parseDefaultElement()DefaultBeanDefinitionDocumentReader->DefaultBeanDefinitionDocumentReader: processBeanDefinition()DefaultBeanDefinitionDocumentReader->BeanDefinitionParserDelegate: parseBeanDefinitionElement()BeanDefinitionParserDelegate->BeanDefinitionParserDelegate: parseBeanDefinitionElement(ele, beanName, containingBean);note right of BeanDefinitionParserDelegate: parsePropertyElements(ele, bd);BeanDefinitionParserDelegate->DefaultBeanDefinitionDocumentReader: return new BeanDefinitionHolderDefaultBeanDefinitionDocumentReader->BeanDefinitionParserDelegate: decorateBeanDefinitionIfRequiredDefaultBeanDefinitionDocumentReader->BeanDefinitionReaderUtils: registerBeanDefinitionBeanDefinitionReaderUtils->DefaultListableBeanFactory: registerBeanDefinitionnote right of DefaultListableBeanFactory: this.beanDefinitionMap.put(beanName, beanDefinition);note right of DefaultListableBeanFactory: this.beanDefinitionNames.add(beanName);DefaultListableBeanFactory->DefaultBeanDefinitionDocumentReader: return DefaultBeanDefinitionDocumentReader->AbstractApplicationContext: obtainFreshBeanFactory() is over,return DefaultListableBeanFactory复制代码

在parsePropertyElements(ele, bd);的时候，把类属性值放入bean中，并返回BeanDefinitionHolder。

在this.beanDefinitionNames.add(beanName);和this.beanDefinitionMap.put(beanName, beanDefinition);时，前者是把beanName放到队列里，后者是把BeanDefinition放到map中，到此注册就完成了。在后面实例化的时候，就是把beanDefinitionMap中的BeanDefinition取出来，逐一实例化

总结来说：

ApplicationContext将解析配置文件的工作委托给BeanDefinitionReader，然后BeanDefinitionReader将配置文件读取为xml的Document文档之后，又委托给BeanDefinitionDocumentReader

BeanDefinitionDocumentReader这个组件是根据xml元素的命名空间和元素名，起到一个路由的作用，实际的解析工作，是委托给BeanDefinitionParserDelegate来完成的

BeanDefinitionParserDelegate的解析工作完成以后，会返回BeanDefinitionHolder给BeanDefinitionDocumentReader，在这里，会委托给DefaultListableBeanFactory完成bean的注册

XmlBeanDefinitionReader（计数、解析XML文档），BeanDefinitionDocumentReader（依赖xml文档，进行解析和注册），BeanDefinitionParserDelegate（实际的解析工作）。可以看出，在解析bean的过程中，这3个组件的分工是比较清晰的，各司其职

getBean方法

ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");        JSONArray person = (JSONArray) context.getBean("aaa");复制代码

补充

中讲了一个BeanDefinitionParseDelegate #parseBeanDefinitionAttributes方法，该方法的执行位置是在上面读取自定义xml解析的时候，运行到BeanDefinitionParserDelegate #parseBeanDefinitionElement方法时，如下图

流程图

这篇文章的顺序比较混乱，我花时间重新画了下时序图，配合文章阅读更容易理解：

时序图文字补充：

SpringMain-> AbstractBeanFactory: getBeanAbstractBeanFactory-> AbstractBeanFactory#doGetBean: doGetBeanAbstractBeanFactory#doGetBean-> DefaultSingletonBeanRegistry: getSingleton(beanName)AbstractBeanFactory#doGetBean-> AbstractBeanFactory#getObjectForBeanInstance: getObjectForBeanInstanceAbstractBeanFactory#doGetBean-> AbstractBeanFactory#getMergedLocalBeanDefinition: getMergedLocalBeanDefinitionAbstractBeanFactory#getMergedLocalBeanDefinition-> AbstractBeanFactory#getMergedLocalBeanDefinition: getMergedBeanDefinitionAbstractBeanFactory#doGetBean-> DefaultSingletonBeanRegistry: registerDependentBeanAbstractBeanFactory#doGetBean-> DefaultSingletonBeanRegistry: getSingletonDefaultSingletonBeanRegistry-> DefaultSingletonBeanRegistry: beforeSingletonCreationAbstractBeanFactory#doGetBean-> AbstractAutowireCapableBeanFactory#createBean: createBeanAbstractAutowireCapableBeanFactory#createBean-> AbstractAutowireCapableBeanFactory#doCreateBean: doCreateBeanAbstractAutowireCapableBeanFactory#doCreateBean-> AbstractAutowireCapableBeanFactory#createBeanInstance: createBeanInstanceAbstractAutowireCapableBeanFactory#createBeanInstance-> AbstractAutowireCapableBeanFactory#instantiateBean: instantiateBeanAbstractAutowireCapableBeanFactory#instantiateBean->SimpleInstantiationStrategy: instantiateAbstractAutowireCapableBeanFactory#doCreateBean-> AbstractAutowireCapableBeanFactory#applyMergedBeanDefinitionPostProcessors: applyMergedBeanDefinitionPostProcessorsAbstractAutowireCapableBeanFactory#applyMergedBeanDefinitionPostProcessors-> AutowiredAnnotationBeanPostProcessor: postProcessMergedBeanDefinitionAutowiredAnnotationBeanPostProcessor-> AutowiredAnnotationBeanPostProcessor: findAutowiringMetadataAutowiredAnnotationBeanPostProcessor-> AutowiredAnnotationBeanPostProcessor: buildAutowiringMetadataAbstractAutowireCapableBeanFactory#doCreateBean-> AbstractAutowireCapableBeanFactory#populateBean: populateBeanAbstractAutowireCapableBeanFactory#populateBean-> AutowiredAnnotationBeanPostProcessor#postProcessPropertyValues: postProcessPropertyValuesAutowiredAnnotationBeanPostProcessor#postProcessPropertyValues-> InjectionMetadata: inject.note right of InjectionMetadata: @ResourceAutowiredAnnotationBeanPostProcessor#postProcessPropertyValues-> AutowiredAnnotationBeanPostProcessor.AutowiredFieldElement: injectnote right of AutowiredAnnotationBeanPostProcessor.AutowiredFieldElement: @Autowired&@ValueAbstractAutowireCapableBeanFactory#populateBean-> AbstractAutowireCapableBeanFactory#populateBean: applyPropertyValues复制代码

在AutowiredAnnotationBeanPostProcessor#buildAutowiringMetadata方法中，Spring会根据注解的不同，例如@Resource或@AutoWired，分别创建不同的类保存返回。这里创建的不同的类会在InjectionMetadata #inject的时候起作用，会调用不同类的inject方法，实现属性的注入。

循环依赖

总结

三层缓存

/** Cache of singleton objects: bean name --> bean instance */private final Map
    
      singletonObjects = new ConcurrentHashMap
     
      (256);/** Cache of singleton factories: bean name --> ObjectFactory */private final Map
      
       > singletonFactories = new HashMap
       
        >(16);/** Cache of early singleton objects: bean name --> bean instance */private final Map
        
          earlySingletonObjects = new HashMap
         
          (16);复制代码

缓存	用途
singletonObjects	用于存放完全初始化好的 bean，从该缓存中取出的 bean 可以直接使用
earlySingletonObjects	存放原始的 bean 对象（尚未填充属性），用于解决循环依赖
singletonFactories	存放 bean 工厂对象，用于解决循环依赖

这里分别举这样三个例子。 A 依赖 B（B不依赖A）

一级缓存 A 依赖 B && B依赖A

三级缓存 A依赖B && B依赖A + B依赖C && C 依赖 A