Spring源码分析总结(一)-IOC容器初始化

女爷i 2022-05-28 06:19 262阅读 0赞

一、IOC容器的初始化过程

IOC容器的初始化是由refresh()方法启动。经常使用的ApplicationContext 有:ClassPathXmlApplicationContext和FileSystemXmlApplicationContext、XmlWebApplicationContext等。都有refresh()方法。

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refresh()方法的这个启动分为三个基本过程:

/**
    	 * Create a new ClassPathXmlApplicationContext with the given parent,
    	 * loading the definitions from the given XML files.
    	 * @param configLocations array of resource locations
    	 * @param refresh whether to automatically refresh the context,
    	 * loading all bean definitions and creating all singletons.
    	 * Alternatively, call refresh manually after further configuring the context.
    	 * @param parent the parent context
    	 * @throws BeansException if context creation failed
    	 * @see #refresh()
    	 */
    	public ClassPathXmlApplicationContext(
    			String[] configLocations, boolean refresh, @Nullable ApplicationContext parent)
    			throws BeansException {
    
    		super(parent);
    		setConfigLocations(configLocations);
    		if (refresh) {
    			refresh();
    		}
    	}

public abstract class AbstractApplicationContext extends DefaultResourceLoader
    		implements ConfigurableApplicationContext {

@Override
    	public void refresh() throws BeansException, IllegalStateException {
    		synchronized (this.startupShutdownMonitor) {
    			//准备刷新的上下文环境 Prepare this context for refreshing.
    			prepareRefresh();
    
    			//初始化BeanFactory,并进行xml文件读取 Tell the subclass to refresh the internal bean factory.
    			ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
    
    			//对BeanFactory进行各种功能填充 Prepare the bean factory for use in this context.
    			prepareBeanFactory(beanFactory);
    
    			try {
    				//子类覆盖方法做额外的处理Allows post-processing of the bean factory in context subclasses.

postProcessBeanFactory(beanFactory);
    
    				//激活各种BeanFactory处理器器,这里只是注册调用在getBean()的时候 Invoke factory processors registered as beans in the context.
    				invokeBeanFactoryPostProcessors(beanFactory);
    
    				//注册拦截Bean创建的Bean处理,这里只是注册调用在getBean()的时候
                                     //Register bean processors that intercept bean creation.
    				registerBeanPostProcessors(beanFactory);
    
    				//为上下文初始化message源,即不同语言的消息体,国际化处理 Initialize message source for this context.
    				initMessageSource();
    
    				//初始化应用消息广播器,并放入（applicationEventMulticaster） Initialize event multicaster for this context.
    				initApplicationEventMulticaster();
    
    				//留给子类来初始化其他的Bean Initialize other special beans in specific context subclasses.
    				onRefresh();
    
    				//在所有注册的bean中查找Listener bean注册到消息广播器中。 Check for listener beans and register them.
    				registerListeners();
    
    				//初始化剩下的单实例(非惰性的) Instantiate all remaining (non-lazy-init) singletons.
    				finishBeanFactoryInitialization(beanFactory);
    
    				//完成刷新过程,通知生命周期处理器lifecycleProcessor刷新过程, 同时发出ContextRefreshEvent通知别人。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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ApplicationContext factory = new FileSystemXmlApplicationContext("F:/workspace/example/src/appcontext.xml");
        IHelloWorld hw = (IHelloWorld)factory.getBean("helloworldbean");
        log.info(hw.getContent("luoshifei"));

//用classpath路径  
ApplicationContext factory = new ClassPathXmlApplicationContext("classpath:appcontext.xml");

Ioc容器的初始化

![70 2][]

1、第一个过程 BeanDefinition的Resource定位

FileSystemXmlApplicationContext/ClassPathXmlApplicationContext ->AbstractApplicationContext类refresh()

\->调用AbstractRefreshableApplicationContext类的refreshBeanFactory()->调用了loadBeanDefinitions(beanFactory);

\->XmlWebApplicationContext类的loadBeanDefinitions->XmlBeanDefinitionReader类的loadBeanDefinitions

\->AbstractBeanDefinitionReader类的loadBeanDefinitions

==>1.调用DefaultResourceLoader的getResource完成具体的Resource定位(Resource resource = resourceLoader.getResource(location);)

\->DefaultResourceLoader类的getResourceByPath(location)完成Resource的定位

==>2.如果跟ResourcePatternResolver相同 ->调用PathMatchingResourcePatternResolver类的getResources方法

在XmlBeanDefinitionReader的基类AbstractBeanDefinition加载读入BeanDefinition

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2、第二个过程 BeanDefinition的载入和解析

AbstractRefreshableApplicationContext类的refreshBeanFactory()->XmlWebApplicationContext类的loadBeanDefinitions

\->AbstractBeanDefinitionReader类的loadBeanDefinitions

\->XmlBeanDefinitionReader类的loadBeanDefinitions()->loadBeanDefinitions()-里面的doLoadBeanDefinitions

\->registerBeanDefinitions(doc, resource)->documentReader.registerBeanDefinitions(doc, createReaderContext(resource));

\->DefaultBeanDefinitionDocumentReader类的registerBeanDefinitions方法->doRegisterBeanDefinitions(root);

\->parseBeanDefinitions(root, this.delegate);->parseBeanDefinitions(Element root, BeanDefinitionParserDelegate delegate)

\->parseDefaultElement(ele, delegate);->processBeanDefinition(ele, delegate);

\->delegate.parseBeanDefinitionElement(ele);->BeanDefinitionParserDelegate类的parseBeanDefinitionElement(ele, null);

\->BeanDefinitionParserDelegate类parseBeanDefinitionElement方法

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3、第三个过程 BeanDefinition在IOC容器中的注册

把解析得到的BeanDefinition设置到hashMap中去。

在DefaultListableBeanFactory中,事通过一个HashMap来持有载入的BeanDefinition的，这个HashMap的定义在DefaultListableBeanFactory中可以看到。

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IOC容器的依赖注入

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1、当用户向IOC容器索要Bean时,也就是如：

IHelloWorld hw = (IHelloWorld)factory.getBean("helloworldbean");

从DefaultListableBeanFactory的基类AbstractBeanFactory类可以看getBean的实现。

//---------------------------------------------------------------------
    	// Implementation of BeanFactory interface
    	//---------------------------------------------------------------------
    
    	@Override
    	public Object getBean(String name) throws BeansException {
    		return doGetBean(name, null, null, false);
    	}

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在createBeanInstance中生成了Bean所包含的java对象,这个对象的生成方式有很多方式,可以通过工厂方法,也可以通过容器的Autowire特性生成,由相关的BeanDefinition来指定。

SimpleInstantiationStrategy类,这个Strategy是spring用来生成bean对象的默认类,它提供了两种实例化Java对象的方法，一种是通过BeanUtils,它提供了JVM的反射功能，一种是通过CGLIB生成。

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