Spring源码分析之Bean的加载流程

spring版本为4.3.6.RELEASE

不管是xml方式配置bean还是基于注解的形式，最终都会调用AbstractApplicationContext的refresh方法：

@Override
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();
        }
    }
}

1、prepareRefresh();

刷新的准备工作，记录容器启动的时间，并设置容器处于活跃状态。

2、ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

刷新并获取beanFactory

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

protected abstract void refreshBeanFactory() throws BeansException, IllegalStateException;

@Override
public abstract ConfigurableListableBeanFactory getBeanFactory() throws IllegalStateException;

这个refreshBeanFactory(),getBeanFactory()由子类AbstractRefreshableApplicationContext来实现：

@Override
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);
    }
}

关键的一个类出来了：

DefaultListableBeanFactory beanFactory = createBeanFactory();

protected DefaultListableBeanFactory createBeanFactory() {
    return new DefaultListableBeanFactory(getInternalParentBeanFactory());
}

在DefaultListableBeanFactory中有了很多实例变量，其中大多是集合形式，用来保存一些必要的对象。

/** Map of bean definition objects, keyed by bean name */
private final Map<String, BeanDefinition> beanDefinitionMap = new ConcurrentHashMap<String, BeanDefinition>(256);

存储Bean名称–>Bean定义映射关系

/** Map of singleton and non-singleton bean names, keyed by dependency type */
private final Map<Class<?>, String[]> allBeanNamesByType = new ConcurrentHashMap<Class<?>, String[]>(64);

/** Map of singleton-only bean names, keyed by dependency type */
private final Map<Class<?>, String[]> singletonBeanNamesByType = new ConcurrentHashMap<Class<?>, String[]>(64);

所有单例和非单例类型和bean的名字数组映射关系

/** List of bean definition names, in registration order */
private volatile List<String> beanDefinitionNames = new ArrayList<String>(256);

所有的Bean definition name的集合

直接看AbstractXmlApplicationContext的loadBeanDefinitions

@Override
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(beanDefin   itionReader);
}

创建bean的解析类：XmlBeanDefinitionReader，将bean的解析工作，交给给BeanDefinitionReader处理。

->XmlBeanDefinitionReader.loadBeanDefinitions(EncodedResource encodedResource)

->XmlBeanDefinitionReader.doLoadBeanDefinitions(InputSource inputSource, Resource resource)

->XmlBeanDefinitionReader.registerBeanDefinitions(Document doc, Resource resource)

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

使用DefaultBeanDefinitionDocumentReader来读取并注册beanDefinition：

->DefaultBeanDefinitionDocumentReader.doRegisterBeanDefinitions(Element root)

protected void doRegisterBeanDefinitions(Element root) {

        BeanDefinitionParserDelegate parent = this.delegate;
        this.delegate = createDelegate(getReaderContext(), root, parent);

        if (this.delegate.isDefaultNamespace(root)) {
            String profileSpec = root.getAttribute(PROFILE_ATTRIBUTE);
            if (StringUtils.hasText(profileSpec)) {
                String[] specifiedProfiles = StringUtils.tokenizeToStringArray(
                        profileSpec, BeanDefinitionParserDelegate.MULTI_VALUE_ATTRIBUTE_DELIMITERS);
                if (!getReaderContext().getEnvironment().acceptsProfiles(specifiedProfiles)) {
                    if (logger.isInfoEnabled()) {
                        logger.info("Skipped XML bean definition file due to specified profiles [" + profileSpec +
                                "] not matching: " + getReaderContext().getResource());
                    }
                    return;
                }
            }
        }

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

        this.delegate = parent;
    }

->DefaultBeanDefinitionDocumentReader.parseBeanDefinitions(Element root, BeanDefinitionParserDelegate delegate)

->DefaultBeanDefinitionDocumentReader.processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate)

protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
    BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
    if (bdHolder != null) {
        bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
        try {
            // Register the final decorated instance.
            BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, getReaderContext().getRegistry());
        }
        catch (BeanDefinitionStoreException ex) {
            getReaderContext().error("Failed to register bean definition with name '" +
                    bdHolder.getBeanName() + "'", ele, ex);
        }
        // Send registration event.
        getReaderContext().fireComponentRegistered(new BeanComponentDefinition(bdHolder));
    }
}

-> BeanDefinitionParserDelegate的parseBeanDefinitionElement方法来解析。

看到这里总算和可见的的配置文件对上了，BeanDefinitionParserDelegate会处理 http://www.springframework.org/schema/beans 命名空间下元素及其属性。

这里会将beanName赋值为配置文件中的id,最终将返回一个new BeanDefinitionHolder(beanDefinition, beanName, aliasesArray);