SSM框架搭建及源码解析--spring容器Bean的注册(二)

Spring 容器启动 refresh（）

想要分析源码，就需要断点反复的去跟代码，理解如何运作的
首先写个测试类，作为容器启动入口

public class TestSpring {    public static void main(String[] args) throws Exception{        ApplicationContext context = new ClassPathXmlApplicationContext("spring-mybatis.xml");        UserService userService=(UserService)context.getBean("userServiceImpl");    }}

查看ClassPathXmlApplicationContext构造方法

    public ClassPathXmlApplicationContext(String[] configLocations, boolean refresh, ApplicationContext parent)            throws BeansException {        super(parent);        setConfigLocations(configLocations);        if (refresh) {            refresh();        }    }

会发现refresh()方法是启动spring容器的关键

    @Override    public void refresh() throws BeansException, IllegalStateException {        synchronized (this.startupShutdownMonitor) {            // Prepare this context for refreshing.            // 记录容器开始时间，设置启动标识            prepareRefresh();            // Tell the subclass to refresh the internal bean factory.            // 解析xml文件，创建beanFactory，这里已经把需要注册的bean的BeanDefinition放入beanDefinitionMap             ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();            // Prepare the bean factory for use in this context.            // 配置工具类            prepareBeanFactory(beanFactory);            try {                // Allows post-processing of the bean factory in context subclasses.                postProcessBeanFactory(beanFactory);                // Invoke factory processors registered as beans in the context.                //执行BeanFactoryPostProcessor类实现的postProcessBeanDefinitionRegistry                invokeBeanFactoryPostProcessors(beanFactory);                // Register bean processors that intercept bean creation.                // 注册实现的BeanPostProcessor类                registerBeanPostProcessors(beanFactory);                // Initialize message source for this context.                // 提供国际化支持                initMessageSource();                // Initialize event multicaster for this context.                // 初始化事件监听                initApplicationEventMulticaster();                // Initialize other special beans in specific context subclasses.                onRefresh();                // Check for listener beans and register them.                // 注册Listener监听类                registerListeners();                // Instantiate all remaining (non-lazy-init) singletons.                // 实例化beanFactory所注册的类                finishBeanFactoryInitialization(beanFactory);                // Last step: publish corresponding event.                // 推送容器启动完毕事件                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;            }        }    }

创建beanFactory容器

首先重点分析obtainFreshBeanFactory()，容器是如何加载bean

    protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {        refreshBeanFactory();        ConfigurableListableBeanFactory beanFactory = getBeanFactory();        if (logger.isDebugEnabled()) {            logger.debug("Bean factory for " + getDisplayName() + ": " + beanFactory);        }        return beanFactory;    }

调用AbstractRefreshableApplicationContext的refreshBeanFactory()加载beanFactory

    protected final void refreshBeanFactory() throws BeansException {        if (hasBeanFactory()) {            destroyBeans();            closeBeanFactory();        }        try {            DefaultListableBeanFactory beanFactory = createBeanFactory();            beanFactory.setSerializationId(getId());            customizeBeanFactory(beanFactory);            loadBeanDefinitions(beanFactory);            synchronized (this.beanFactoryMonitor) {                this.beanFactory = beanFactory;            }        }        catch (IOException ex) {            throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);        }    }

调用AbstractXmlApplicationContext的loadBeanDefinitions()，创建xml解析器

    protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {        // Create a new XmlBeanDefinitionReader for the given BeanFactory.        XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);        // Configure the bean definition reader with this context's        // resource loading environment.        beanDefinitionReader.setEnvironment(this.getEnvironment());        beanDefinitionReader.setResourceLoader(this);        beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this));        // Allow a subclass to provide custom initialization of the reader,        // then proceed with actually loading the bean definitions.        initBeanDefinitionReader(beanDefinitionReader);        loadBeanDefinitions(beanDefinitionReader);    }

调用loadBeanDefinitions()解析配置文件

    protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws BeansException, IOException {        Resource[] configResources = getConfigResources();        if (configResources != null) {            reader.loadBeanDefinitions(configResources);        }        String[] configLocations = getConfigLocations();        if (configLocations != null) {            reader.loadBeanDefinitions(configLocations);        }    }

跳过中间一些调用，继续跟到XmlBeanDefinitionReader的loadBeanDefinitions()
中调用doLoadBeanDefinitions(),doLoadDocument解析xml文件的整个doc结构

            Document doc = doLoadDocument(inputSource, resource);            return registerBeanDefinitions(doc, resource);

调用registerBeanDefinitions()方法注册BeanDefinitions

    public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {        BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();        documentReader.setEnvironment(getEnvironment());        int countBefore = getRegistry().getBeanDefinitionCount();        documentReader.registerBeanDefinitions(doc, createReaderContext(resource));        return getRegistry().getBeanDefinitionCount() - countBefore;    }

调用BeanDefinitionDocumentReader接口的registerBeanDefinitions()方法
具体实现见DefaultBeanDefinitionDocumentReader的registerBeanDefinitions()
调用doRegisterBeanDefinitions解析

        preProcessXml(root);        parseBeanDefinitions(root, this.delegate);        postProcessXml(root);

接下来就是解析的关键方法parseBeanDefinitions()

    protected void parseBeanDefinitions(Element root, BeanDefinitionParserDelegate delegate) {        if (delegate.isDefaultNamespace(root)) {            NodeList nl = root.getChildNodes();            for (int i = 0; i < nl.getLength(); i++) {                Node node = nl.item(i);                if (node instanceof Element) {                    Element ele = (Element) node;                    if (delegate.isDefaultNamespace(ele)) {                        parseDefaultElement(ele, delegate);                    }                    else {                        delegate.parseCustomElement(ele);                    }                }            }        }        else {            delegate.parseCustomElement(root);        }    }

    public BeanDefinition parseCustomElement(Element ele, BeanDefinition containingBd) {        String namespaceUri = getNamespaceURI(ele);        NamespaceHandler handler = this.readerContext.getNamespaceHandlerResolver().resolve(namespaceUri);        if (handler == null) {            error("Unable to locate Spring NamespaceHandler for XML schema namespace [" + namespaceUri + "]", ele);            return null;        }        return handler.parse(ele, new ParserContext(this.readerContext, this, containingBd));    }

逐行读取xml配置文件，解析对应的NamespaceHandler接口实现的处理类
其中以配置文件中

<context:component-scan base-package="com.demo"/>

为例
调用的是ContextNamespaceHandler中注册的ComponentScanBeanDefinitionParser解析器

        registerBeanDefinitionParser("property-placeholder", new PropertyPlaceholderBeanDefinitionParser());        registerBeanDefinitionParser("property-override", new PropertyOverrideBeanDefinitionParser());        registerBeanDefinitionParser("annotation-config", new AnnotationConfigBeanDefinitionParser());        registerBeanDefinitionParser("component-scan", new ComponentScanBeanDefinitionParser());        registerBeanDefinitionParser("load-time-weaver", new LoadTimeWeaverBeanDefinitionParser());        registerBeanDefinitionParser("spring-configured", new SpringConfiguredBeanDefinitionParser());        registerBeanDefinitionParser("mbean-export", new MBeanExportBeanDefinitionParser());        registerBeanDefinitionParser("mbean-server", new MBeanServerBeanDefinitionParser());

调用的是ContextNamespaceHandler中注册的ComponentScanBeanDefinitionParser解析器,parse()方法

    public BeanDefinition parse(Element element, ParserContext parserContext) {        String basePackage = element.getAttribute(BASE_PACKAGE_ATTRIBUTE);        basePackage = parserContext.getReaderContext().getEnvironment().resolvePlaceholders(basePackage);        String[] basePackages = StringUtils.tokenizeToStringArray(basePackage,                ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS);        // Actually scan for bean definitions and register them.        ClassPathBeanDefinitionScanner scanner = configureScanner(parserContext, element);        Set<BeanDefinitionHolder> beanDefinitions = scanner.doScan(basePackages);        registerComponents(parserContext.getReaderContext(), beanDefinitions, element);        return null;    }

通过调用ClassPathBeanDefinitionScanner.doScan()方法来获得BeanDefinitionHolders

    protected Set<BeanDefinitionHolder> doScan(String... basePackages) {        Assert.notEmpty(basePackages, "At least one base package must be specified");        Set<BeanDefinitionHolder> beanDefinitions = new LinkedHashSet<BeanDefinitionHolder>();        for (String basePackage : basePackages) {            Set<BeanDefinition> candidates = findCandidateComponents(basePackage);            for (BeanDefinition candidate : candidates) {                ScopeMetadata scopeMetadata = this.scopeMetadataResolver.resolveScopeMetadata(candidate);                candidate.setScope(scopeMetadata.getScopeName());                String beanName = this.beanNameGenerator.generateBeanName(candidate, this.registry);                if (candidate instanceof AbstractBeanDefinition) {                    postProcessBeanDefinition((AbstractBeanDefinition) candidate, beanName);                }                if (candidate instanceof AnnotatedBeanDefinition) {                    AnnotationConfigUtils.processCommonDefinitionAnnotations((AnnotatedBeanDefinition) candidate);                }                if (checkCandidate(beanName, candidate)) {                    BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(candidate, beanName);                    definitionHolder = AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, definitionHolder, this.registry);                    beanDefinitions.add(definitionHolder);                    registerBeanDefinition(definitionHolder, this.registry);                }            }        }        return beanDefinitions;    }

会扫描配置包下的类，是否有对应注解，然后调用registerBeanDefinition(),
BeanDefinitionReaderUtils.registerBeanDefinition()注册到beanFactory的beanDefinitionMap中

    public static void registerBeanDefinition(            BeanDefinitionHolder definitionHolder, BeanDefinitionRegistry registry)            throws BeanDefinitionStoreException {        // Register bean definition under primary name.        String beanName = definitionHolder.getBeanName();        registry.registerBeanDefinition(beanName, definitionHolder.getBeanDefinition());        // Register aliases for bean name, if any.        String[] aliases = definitionHolder.getAliases();        if (aliases != null) {            for (String alias : aliases) {                registry.registerAlias(beanName, alias);            }        }    }

        oldBeanDefinition = this.beanDefinitionMap.get(beanName);        if (oldBeanDefinition != null) {            //beanFactory的配置，是否允许同名的bean             if (!isAllowBeanDefinitionOverriding()) {                throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,                        "Cannot register bean definition [" + beanDefinition + "] for bean '" + beanName +                        "': There is already [" + oldBeanDefinition + "] bound.");            }            else if (oldBeanDefinition.getRole() < beanDefinition.getRole()) {                // e.g. was ROLE_APPLICATION, now overriding with ROLE_SUPPORT or ROLE_INFRASTRUCTURE                if (this.logger.isWarnEnabled()) {                    this.logger.warn("Overriding user-defined bean definition for bean '" + beanName +                            "' with a framework-generated bean definition: replacing [" +                            oldBeanDefinition + "] with [" + beanDefinition + "]");                }            }            else {                if (this.logger.isInfoEnabled()) {                    this.logger.info("Overriding bean definition for bean '" + beanName +                            "': replacing [" + oldBeanDefinition + "] with [" + beanDefinition + "]");                }            }        }        else {            this.beanDefinitionNames.add(beanName);            this.manualSingletonNames.remove(beanName);            this.frozenBeanDefinitionNames = null;        }        this.beanDefinitionMap.put(beanName, beanDefinition);

通过这一系列过程，把带有注解的类转换为BeanDefinition,BeanDefinition接口是用于描述这个类的相关信息，例如类信息，依赖关系等

    /** Map of bean definition objects, keyed by bean name */    private final Map<String, BeanDefinition> beanDefinitionMap = new ConcurrentHashMap<String, BeanDefinition>(64);

而beanDefinitionMap是spring容器关键所在，存储类的注册信息。