其他更多java基础文章:
java基础学习(目录)
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");
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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();
}
}
}
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下面讲解的重点是obtainFreshBeanFactory()
这个方法。
推荐博客
- 通过源码阅读和时序图来彻底弄懂Spring容器:这篇文章阅读顺序非常好,顺着代码运行的顺序,并且有时序图辅助学习,但是单看这一篇,还是有点迷茫,主要是对一些细节方面不够,而且总结也比较粗。应配合下面文章一起学习。
- Spring Ioc 源码分析(一)--Spring Ioc容器的加载:这一系列一共有四章,对细节讲述比较清楚。分成三个模块来讲解,对方法的总结和大白话描述多,更易理解。缺点就是顺序不够好,经常从这跳到另一个地方。
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: 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");
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推荐博客
- 【Spring源码学习】getBean (上):这篇文章顺序比较好,方便第一次看源码跟着步骤,缺点就是讲的比较少,没有什么总结
- GetBean源码全解读:这篇文章总结比较多,缺点是是结构顺序好乱,我会在下面补充其顺序
- Spring IOC 容器源码分析 - 获取单例 bean
补充
【Spring源码学习】getBean (上)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
GetBean源码全解读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: 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
推荐博客
总结
三层缓存
/** 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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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
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