Spring源碼分析

時間 2019-11-07

標籤 spring 源碼分析欄目 Spring 简体版

原文原文鏈接

其餘更多java基礎文章：
java基礎學習(目錄)java

Spring源碼太大了，對於一個技術不深的我來講，第一次啃會很艱難，因而我決定一個模塊一個模塊的看，而且將在學習的過程當中，以爲很不錯的文章記錄下來。建議你們先閱讀推薦博客，而後再看個人補充。當前Spring版本4.3.18spring

Spring讀取自定義xml文件解析

ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");
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重點

整個容器的啓動流程，都在AbstractApplicationContext的refresh()的模板方法中了緩存

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(); } } } 複製代碼

下面講解的重點是obtainFreshBeanFactory()這個方法。bash

總結

時序圖我花時間從新畫了一幅，可是流程太長，整條流程保存的畫質不怎麼好。因此我把總體和局部時序圖都畫出來，方便你們對比app

下面是整個時序圖的流轉過程文字文字補充：源碼分析

SpringMain->ClassPathXmlApplicationContext: new ClassPathXmlApplicationContext("applicationContext.xml");
ClassPathXmlApplicationContext->AbstractRefreshableConfigApplicationContext: setConfigLocations()
AbstractRefreshableConfigApplicationContext->ClassPathXmlApplicationContext: return
ClassPathXmlApplicationContext->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 BeanDefinitionHolder
DefaultBeanDefinitionDocumentReader->BeanDefinitionParserDelegate: decorateBeanDefinitionIfRequired
DefaultBeanDefinitionDocumentReader->BeanDefinitionReaderUtils: registerBeanDefinition
BeanDefinitionReaderUtils->DefaultListableBeanFactory: registerBeanDefinition
note 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
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在parsePropertyElements(ele, bd);的時候，把類屬性值放入bean中，並返回BeanDefinitionHolder。
在this.beanDefinitionNames.add(beanName);和this.beanDefinitionMap.put(beanName, beanDefinition);時，前者是把beanName放到隊列裏，後者是把BeanDefinition放到map中，到此註冊就完成了。在後面實例化的時候，就是把beanDefinitionMap中的BeanDefinition取出來，逐一實例化

總結來講：

ApplicationContext將解析配置文件的工做委託給BeanDefinitionReader，而後BeanDefinitionReader將配置文件讀取爲xml的Document文檔以後，又委託給BeanDefinitionDocumentReader
BeanDefinitionDocumentReader這個組件是根據xml元素的命名空間和元素名，起到一個路由的做用，實際的解析工做，是委託給BeanDefinitionParserDelegate來完成的
BeanDefinitionParserDelegate的解析工做完成之後，會返回BeanDefinitionHolder給BeanDefinitionDocumentReader，在這裏，會委託給DefaultListableBeanFactory完成bean的註冊
XmlBeanDefinitionReader（計數、解析XML文檔），BeanDefinitionDocumentReader（依賴xml文檔，進行解析和註冊），BeanDefinitionParserDelegate（實際的解析工做）。能夠看出，在解析bean的過程當中，這3個組件的分工是比較清晰的，各司其職

getBean方法

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

【Spring源碼學習】getBean （上）中講了一個BeanDefinitionParseDelegate #parseBeanDefinitionAttributes方法，該方法的執行位置是在上面讀取自定義xml解析的時候，運行到BeanDefinitionParserDelegate #parseBeanDefinitionElement方法時，以下圖post

流程圖

GetBean源碼全解讀這篇文章的順序比較混亂，我花時間從新畫了下時序圖，配合文章閱讀更容易理解：學習

時序圖文字補充：ui

SpringMain-> AbstractBeanFactory: getBean
AbstractBeanFactory-> AbstractBeanFactory#doGetBean: doGetBean
AbstractBeanFactory#doGetBean-> DefaultSingletonBeanRegistry: getSingleton(beanName)
AbstractBeanFactory#doGetBean-> AbstractBeanFactory#getObjectForBeanInstance: getObjectForBeanInstance
AbstractBeanFactory#doGetBean-> AbstractBeanFactory#getMergedLocalBeanDefinition: getMergedLocalBeanDefinition
AbstractBeanFactory#getMergedLocalBeanDefinition-> AbstractBeanFactory#getMergedLocalBeanDefinition: getMergedBeanDefinition
AbstractBeanFactory#doGetBean-> DefaultSingletonBeanRegistry: registerDependentBean
AbstractBeanFactory#doGetBean-> DefaultSingletonBeanRegistry: getSingleton
DefaultSingletonBeanRegistry-> DefaultSingletonBeanRegistry: beforeSingletonCreation
AbstractBeanFactory#doGetBean-> AbstractAutowireCapableBeanFactory#createBean: createBean
AbstractAutowireCapableBeanFactory#createBean-> AbstractAutowireCapableBeanFactory#doCreateBean: doCreateBean
AbstractAutowireCapableBeanFactory#doCreateBean-> AbstractAutowireCapableBeanFactory#createBeanInstance: createBeanInstance
AbstractAutowireCapableBeanFactory#createBeanInstance-> AbstractAutowireCapableBeanFactory#instantiateBean: instantiateBean
AbstractAutowireCapableBeanFactory#instantiateBean->SimpleInstantiationStrategy: instantiate
AbstractAutowireCapableBeanFactory#doCreateBean-> AbstractAutowireCapableBeanFactory#applyMergedBeanDefinitionPostProcessors: applyMergedBeanDefinitionPostProcessors
AbstractAutowireCapableBeanFactory#applyMergedBeanDefinitionPostProcessors-> AutowiredAnnotationBeanPostProcessor: postProcessMergedBeanDefinition
AutowiredAnnotationBeanPostProcessor-> AutowiredAnnotationBeanPostProcessor: findAutowiringMetadata
AutowiredAnnotationBeanPostProcessor-> AutowiredAnnotationBeanPostProcessor: buildAutowiringMetadata
AbstractAutowireCapableBeanFactory#doCreateBean-> AbstractAutowireCapableBeanFactory#populateBean: populateBean
AbstractAutowireCapableBeanFactory#populateBean-> AutowiredAnnotationBeanPostProcessor#postProcessPropertyValues: postProcessPropertyValues
AutowiredAnnotationBeanPostProcessor#postProcessPropertyValues-> InjectionMetadata: inject.
note right of InjectionMetadata: @Resource
AutowiredAnnotationBeanPostProcessor#postProcessPropertyValues-> AutowiredAnnotationBeanPostProcessor.AutowiredFieldElement: inject
note right of AutowiredAnnotationBeanPostProcessor.AutowiredFieldElement: @Autowired&@Value
AbstractAutowireCapableBeanFactory#populateBean-> AbstractAutowireCapableBeanFactory#populateBean: applyPropertyValues
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在AutowiredAnnotationBeanPostProcessor#buildAutowiringMetadata方法中，Spring會根據註解的不一樣，例如@Resource或@AutoWired，分別建立不一樣的類保存返回。這裏建立的不一樣的類會在InjectionMetadata #inject的時候起做用，會調用不一樣類的inject方法，實現屬性的注入。this

循環依賴

總結

三層緩存

/** Cache of singleton objects: bean name --> bean instance */
private final Map<String, Object> singletonObjects = new ConcurrentHashMap<String, Object>(256);

/** Cache of singleton factories: bean name --> ObjectFactory */
private final Map<String, ObjectFactory<?>> singletonFactories = new HashMap<String, ObjectFactory<?>>(16);

/** Cache of early singleton objects: bean name --> bean instance */
private final Map<String, Object> earlySingletonObjects = new HashMap<String, Object>(16);
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緩存	用途
singletonObjects	用於存放徹底初始化好的 bean，從該緩存中取出的 bean 能夠直接使用
earlySingletonObjects	存放原始的 bean 對象（還沒有填充屬性），用於解決循環依賴
singletonFactories	存放 bean 工廠對象，用於解決循環依賴