XmlBeanFactory

类结构图

代码

import org.springframework.beans.factory.BeanFactory;
import org.springframework.beans.factory.xml.XmlBeanFactory;
import org.springframework.core.io.ClassPathResource;
public class XmlBeanFactoryTest {
    public static void main(String[] args) {
        // 资源加载
        ClassPathResource classPathResource = new ClassPathResource("spring-bean.xml");
        // XmlBeanFactory 加载资源并解析注册bean
        BeanFactory beanFactory = new XmlBeanFactory(classPathResource);
        // BeanFactory.getBean();
        UserBean userBean = (UserBean) beanFactory.getBean("userBean");
        System.out.println(userBean.getName());
    }
}

源码解析

XmlBeanFactory解析Xml是使用了XmlBeanDefinitionReader.loadBeanDefinition()方法

@Deprecated
@SuppressWarnings({"serial", "all"})
public class XmlBeanFactory extends DefaultListableBeanFactory {
    private final XmlBeanDefinitionReader reader = new XmlBeanDefinitionReader(this);
    /**
     * Create a new XmlBeanFactory with the given resource,
     * which must be parsable using DOM.
     * @param resource XML resource to load bean definitions from
     * @throws BeansException in case of loading or parsing errors
     */
    public XmlBeanFactory(Resource resource) throws BeansException {
        this(resource, null);
    }
    /**
     * Create a new XmlBeanFactory with the given input stream,
     * which must be parsable using DOM.
     * @param resource XML resource to load bean definitions from
     * @param parentBeanFactory parent bean factory
     * @throws BeansException in case of loading or parsing errors
     */
    public XmlBeanFactory(Resource resource, BeanFactory parentBeanFactory) throws BeansException {
        super(parentBeanFactory);
        this.reader.loadBeanDefinitions(resource);
    }
}

this.reader.loadBeanDefinitions(resource);

/**
     * Load bean definitions from the specified XML file.
     * @param resource the resource descriptor for the XML file
     * @return the number of bean definitions found
     * @throws BeanDefinitionStoreException in case of loading or parsing errors
     */
    public int loadBeanDefinitions(Resource resource) throws BeanDefinitionStoreException {
        return loadBeanDefinitions(new EncodedResource(resource));
    }
    /**
     * Load bean definitions from the specified XML file.
     * @param encodedResource the resource descriptor for the XML file,
     * allowing to specify an encoding to use for parsing the file
     * @return the number of bean definitions found
     * @throws BeanDefinitionStoreException in case of loading or parsing errors
     */
    public int loadBeanDefinitions(EncodedResource encodedResource) throws BeanDefinitionStoreException {
        Assert.notNull(encodedResource, "EncodedResource must not be null");
        if (logger.isInfoEnabled()) {
            logger.info("Loading XML bean definitions from " + encodedResource.getResource());
        }
        // 通过属性来记录已经加载的资源
        Set<EncodedResource> currentResources = this.resourcesCurrentlyBeingLoaded.get();
        if (currentResources == null) {
            currentResources = new HashSet<EncodedResource>(4);
            this.resourcesCurrentlyBeingLoaded.set(currentResources);
        }
        if (!currentResources.add(encodedResource)) {
            throw new BeanDefinitionStoreException(
                    "Detected cyclic loading of " + encodedResource + " - check your import definitions!");
        }
        try {
            // 从encodedResource已经封装的Resource获取InputStream
            InputStream inputStream = encodedResource.getResource().getInputStream();
            try {
                //InputSource 并不是spring的，而是 org.xml.sax 
                InputSource inputSource = new InputSource(inputStream);
                //如果encodedResource 中的 Encoding 不是 null 则同步设置 InputSource的 Encoding
                if (encodedResource.getEncoding() != null) {
                    inputSource.setEncoding(encodedResource.getEncoding());
                }
                //加载bean的Definitions 将xml中的信息加载到Definition中，并且在内存中注册的也是key+definitions
                return doLoadBeanDefinitions(inputSource, encodedResource.getResource());
            }
            finally {
                inputStream.close();
            }
        }
        catch (IOException ex) {
            throw new BeanDefinitionStoreException(
                    "IOException parsing XML document from " + encodedResource.getResource(), ex);
        }
        finally {
            currentResources.remove(encodedResource);
            if (currentResources.isEmpty()) {
                this.resourcesCurrentlyBeingLoaded.remove();
            }
        }
    }

上述源码可能看着比较长,但实际上这里并不是真正解析的地方，在这里做了如下： 1:从encodedResource已经封装的Resource获取InputStream； 2:如果encodedResource 中的 Encoding 不是 null 则同步设置 InputSource的 Encoding； 3:将解析动作委托给doLoadBeanDefinitions实现；

doLoadBeanDefinitions(inputSource, encodedResource.getResource())

/**
     * Actually load bean definitions from the specified XML file.
     * @param inputSource the SAX InputSource to read from
     * @param resource the resource descriptor for the XML file
     * @return the number of bean definitions found
     * @throws BeanDefinitionStoreException in case of loading or parsing errors
     */
    protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)
            throws BeanDefinitionStoreException {
        try {
            int validationMode = getValidationModeForResource(resource);
            //加载 Document
            Document doc = this.documentLoader.loadDocument(
                    inputSource, getEntityResolver(), this.errorHandler, validationMode, isNamespaceAware());
            //注册 bean
            return registerBeanDefinitions(doc, resource);
        }
        catch (BeanDefinitionStoreException ex) {
            throw ex;
        }
        catch (SAXParseException ex) {
            throw new XmlBeanDefinitionStoreException(resource.getDescription(),
                    "Line " + ex.getLineNumber() + " in XML document from " + resource + " is invalid", ex);
        }
        catch (SAXException ex) {
            throw new XmlBeanDefinitionStoreException(resource.getDescription(),
                    "XML document from " + resource + " is invalid", ex);
        }
        catch (ParserConfigurationException ex) {
            throw new BeanDefinitionStoreException(resource.getDescription(),
                    "Parser configuration exception parsing XML from " + resource, ex);
        }
        catch (IOException ex) {
            throw new BeanDefinitionStoreException(resource.getDescription(),
                    "IOException parsing XML document from " + resource, ex);
        }
        catch (Throwable ex) {
            throw new BeanDefinitionStoreException(resource.getDescription(),
                    "Unexpected exception parsing XML document from " + resource, ex);
        }
    }

当我们看着这个方法的时候，依旧不是真正的解析或注册的方法，在这里只是做了Document的加载，并将后续工作委托给了registerBeanDefinitions

registerBeanDefinitions(doc, resource)

/**
     * Register the bean definitions contained in the given DOM document.
     * Called by {@code loadBeanDefinitions}.
     * <p>Creates a new instance of the parser class and invokes
     * {@code registerBeanDefinitions} on it.
     * @param doc the DOM document
     * @param resource the resource descriptor (for context information)
     * @return the number of bean definitions found
     * @throws BeanDefinitionStoreException in case of parsing errors
     * @see #loadBeanDefinitions
     * @see #setDocumentReaderClass
     * @see BeanDefinitionDocumentReader#registerBeanDefinitions
     */
    @SuppressWarnings("deprecation")
    public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
        //实例化 BeanDefinitionDocumentReader
        BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
        documentReader.setEnvironment(getEnvironment());
        //获取之前的beanDefinition加载个数
        int countBefore = getRegistry().getBeanDefinitionCount();
        //加载xml及注册bean
        documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
        //记录本次加载个数
        return getRegistry().getBeanDefinitionCount() - countBefore;
    }

documentReader.registerBeanDefinitions(doc, createReaderContext(resource))

/**
     * This implementation parses bean definitions according to the "spring-beans" XSD
     * (or DTD, historically).
     * <p>Opens a DOM Document; then initializes the default settings
     * specified at the {@code <beans/>} level; then parses the contained bean definitions.
     */
    public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) {
        this.readerContext = readerContext;
        logger.debug("Loading bean definitions");
        //实例化 ReaderContext
        Element root = doc.getDocumentElement();
        //注册
        doRegisterBeanDefinitions(root);
    }

registerBeanDefinitions并没有做什么，我们继续看doRegisterBeanDefinitions方法

doRegisterBeanDefinitions(root)

protected void doRegisterBeanDefinitions(Element root) {
        String profileSpec = root.getAttribute(PROFILE_ATTRIBUTE);
        if (StringUtils.hasText(profileSpec)) {
            String[] specifiedProfiles = StringUtils.tokenizeToStringArray(
                    profileSpec, BeanDefinitionParserDelegate.MULTI_VALUE_ATTRIBUTE_DELIMITERS);
            if (!getEnvironment().acceptsProfiles(specifiedProfiles)) {
                return;
            }
        }
        // Any nested <beans> elements will cause recursion in this method. In
        // order to propagate and preserve <beans> default-* attributes correctly,
        // keep track of the current (parent) delegate, which may be null. Create
        // the new (child) delegate with a reference to the parent for fallback purposes,
        // then ultimately reset this.delegate back to its original (parent) reference.
        // this behavior emulates a stack of delegates without actually necessitating one.
        BeanDefinitionParserDelegate parent = this.delegate;
        this.delegate = createDelegate(this.readerContext, root, parent);
        //解析前处理， 内容null 留个子类实现
        preProcessXml(root);
        //解析
        parseBeanDefinitions(root, this.delegate);
        //解析后处理， 内容null 留个子类实现
        postProcessXml(root);
        this.delegate = parent;
    }

在doRegisterBeanDefinitions方法中验证xml的namespace,最重要的方法是parseBeanDefinitions，parseBeanDefinitions方法进行了解析操作；

parseBeanDefinitions(root, this.delegate);

/**
     * Parse the elements at the root level in the document:
     * "import", "alias", "bean".
     * @param root the DOM root element of the document
     */
    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)) {
                        //对默认标签处理
                        parseDefaultElement(ele, delegate);
                    }
                    else {
                        //对自定义标签处理
                        delegate.parseCustomElement(ele);
                    }
                }
            }
        }
        else {
            //对自定义标签处理
            delegate.parseCustomElement(root);
        }
    }

parseBeanDefinitions方法中已经开始对标签进行解析，区分默认标签和自定义标签，我们本次只对默认标签的源码进行解析，自定义标签自行DeBug

parseDefaultElement(ele, delegate);

private void parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate) {
        //解析import标签    
        if (delegate.nodeNameEquals(ele, IMPORT_ELEMENT)) {
            importBeanDefinitionResource(ele);
        }
        //解析alias标签并注册
        else if (delegate.nodeNameEquals(ele, ALIAS_ELEMENT)) {
            processAliasRegistration(ele);
        }
        //解析bean标签并注册
        else if (delegate.nodeNameEquals(ele, BEAN_ELEMENT)) {
            processBeanDefinition(ele, delegate);
        }
        //解析beans标签
        else if (delegate.nodeNameEquals(ele, NESTED_BEANS_ELEMENT)) {
            // recurse
            doRegisterBeanDefinitions(ele);
        }
    }

到这里我们可以看到，spring对import/bean/alias/beans的解析过程，对于beans的解析无非就是解析beans中的bean标签，spring直接又重新调用了doRegisterBeanDefinitions方法，我们接下来进行对bean标签的解析

processBeanDefinition(ele, delegate);

/**
     * Process the given bean element, parsing the bean definition
     * and registering it with the registry.
     */
    protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
        //委托BeanDefinitionParserDelegate的parseBeanDefinitionElement方法进行元素解析并返回
        //BeanDefinitionHolder实例，BeanDefinitionHolder已经包含了配置文件中的各种属性
        BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
        //当BeanDefinitionHolder返回不null的情况，弱存在默认标签下的子标签再有自定义的属性，还需要再次解析
        if (bdHolder != null) {
            //解析默认标签中的自定义标签
            bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
            try {
                // Register the final decorated instance.
                // 进行实例注册注册操作是BeanDefinitionReaderUtisl.registerBeanDefinition进行处理
                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));
        }
    }

在processBeanDefinition方法中，spring做了两件事情： 1：委托BeanDefinitionParserDelegate的parseBeanDefinitionElement方法进行元素解析并返回BeanDefinitionHolder实例，BeanDefinitionHolder已经包含了配置文件中的各种属性 2：通过上获得的BeanDefinitionHolder进行bean的注册操作，通BeanDefinitionReaderUtils.registerBeanDefinition方法；

delegate.parseBeanDefinitionElement(ele);

/**
     * Parses the supplied {@code <bean>} element. May return {@code null}
     * if there were errors during parse. Errors are reported to the
     * {@link org.springframework.beans.factory.parsing.ProblemReporter}.
     */
    public BeanDefinitionHolder parseBeanDefinitionElement(Element ele, BeanDefinition containingBean) {
        //解析id属性
        String id = ele.getAttribute(ID_ATTRIBUTE);
        //解析name属性
        String nameAttr = ele.getAttribute(NAME_ATTRIBUTE);
        //分割name属性
        List<String> aliases = new ArrayList<String>();
        if (StringUtils.hasLength(nameAttr)) {
            String[] nameArr = StringUtils.tokenizeToStringArray(nameAttr, MULTI_VALUE_ATTRIBUTE_DELIMITERS);
            aliases.addAll(Arrays.asList(nameArr));
        }
        String beanName = id;
        if (!StringUtils.hasText(beanName) && !aliases.isEmpty()) {
            beanName = aliases.remove(0);
            if (logger.isDebugEnabled()) {
                logger.debug("No XML 'id' specified - using '" + beanName +
                        "' as bean name and " + aliases + " as aliases");
            }
        }
        if (containingBean == null) {
            checkNameUniqueness(beanName, aliases, ele);
        }
        //将信息封装到 beanDefinition中
        AbstractBeanDefinition beanDefinition = parseBeanDefinitionElement(ele, beanName, containingBean);
        if (beanDefinition != null) {
            if (!StringUtils.hasText(beanName)) {
                try {
                    //beanname不存在则使用默认规则创建
                    if (containingBean != null) {
                        beanName = BeanDefinitionReaderUtils.generateBeanName(
                                beanDefinition, this.readerContext.getRegistry(), true);
                    }
                    else {
                        beanName = this.readerContext.generateBeanName(beanDefinition);
                        // Register an alias for the plain bean class name, if still possible,
                        // if the generator returned the class name plus a suffix.
                        // This is expected for Spring 1.2/2.0 backwards compatibility.
                        String beanClassName = beanDefinition.getBeanClassName();
                        if (beanClassName != null &&
                                beanName.startsWith(beanClassName) && beanName.length() > beanClassName.length() &&
                                !this.readerContext.getRegistry().isBeanNameInUse(beanClassName)) {
                            aliases.add(beanClassName);
                        }
                    }
                    if (logger.isDebugEnabled()) {
                        logger.debug("Neither XML 'id' nor 'name' specified - " +
                                "using generated bean name [" + beanName + "]");
                    }
                }
                catch (Exception ex) {
                    error(ex.getMessage(), ele);
                    return null;
                }
            }
            String[] aliasesArray = StringUtils.toStringArray(aliases);
            return new BeanDefinitionHolder(beanDefinition, beanName, aliasesArray);
        }
        return null;
    }

在parseBeanDefinitionElement方法中做了三件事： 1：解析id/name； 2：检查name的唯一性； 3：将信息封装到 beanDefinition中，接下来直接看parseBeanDefinitionElement方法；

parseBeanDefinitionElement(ele, beanName, containingBean);

/**
     * Parse the bean definition itself, without regard to name or aliases. May return
     * {@code null} if problems occurred during the parsing of the bean definition.
     */
    public AbstractBeanDefinition parseBeanDefinitionElement(
            Element ele, String beanName, BeanDefinition containingBean) {
        this.parseState.push(new BeanEntry(beanName));
        String className = null;
        //解析classname属性
        if (ele.hasAttribute(CLASS_ATTRIBUTE)) {
            className = ele.getAttribute(CLASS_ATTRIBUTE).trim();
        }
        try {
            String parent = null;
            //解析parent属性
            if (ele.hasAttribute(PARENT_ATTRIBUTE)) {
                parent = ele.getAttribute(PARENT_ATTRIBUTE);
            }
            //创建用于承载属性的AbstractBeanDefinition类型的
            AbstractBeanDefinition bd = createBeanDefinition(className, parent);
            //解析bean的各种属性
            parseBeanDefinitionAttributes(ele, beanName, containingBean, bd);
            //提取description
            bd.setDescription(DomUtils.getChildElementValueByTagName(ele, DESCRIPTION_ELEMENT));
            //解析meta （元数据）
            parseMetaElements(ele, bd);
            //解析Lookup-method
            parseLookupOverrideSubElements(ele, bd.getMethodOverrides());
            //解析replaced-method
            parseReplacedMethodSubElements(ele, bd.getMethodOverrides());
            //构造函数 参数
            //解析constructor-arg
            parseConstructorArgElements(ele, bd);
            //解析Property
            parsePropertyElements(ele, bd);
            //解析Qualifier
            parseQualifierElements(ele, bd);
            bd.setResource(this.readerContext.getResource());
            bd.setSource(extractSource(ele));
            return bd;
        }
        catch (ClassNotFoundException ex) {
            error("Bean class [" + className + "] not found", ele, ex);
        }
        catch (NoClassDefFoundError err) {
            error("Class that bean class [" + className + "] depends on not found", ele, err);
        }
        catch (Throwable ex) {
            error("Unexpected failure during bean definition parsing", ele, ex);
        }
        finally {
            this.parseState.pop();
        }
        return null;
    }

通过上述代码我们可以看到这里首先是实例化了一个AbstractBeanDefinition来承载各种xml属性，接下来通过parseBeanDefinitionAttributes方法解析了xml中的各种你属性值，然后在解析lookUp-method(方法注入)，replaced-method(替换方法或方法返回值)，构造函数参数constructor-arg，property属性，Qualifier属性等；上述方法的源码就不一一展示了，无非都是通过Element进行解析；

BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, getReaderContext().getRegistry());

下面代码是上述代码块调用了registry.registerBeanDefinition(beanName, definitionHolder.getBeanDefinition())，真正具体实现如下（使用了DefaultListableBeanFactory类实现的方法）

public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition)
            throws BeanDefinitionStoreException {
        Assert.hasText(beanName, "Bean name must not be empty");
        Assert.notNull(beanDefinition, "BeanDefinition must not be null");
        if (beanDefinition instanceof AbstractBeanDefinition) {
            try {
                 //校验 MethodOverrides
                ((AbstractBeanDefinition) beanDefinition).validate();
            }
            catch (BeanDefinitionValidationException ex) {
                throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
                        "Validation of bean definition failed", ex);
            }
        }
        BeanDefinition oldBeanDefinition;
        synchronized (this.beanDefinitionMap) {
            oldBeanDefinition = this.beanDefinitionMap.get(beanName);
            if (oldBeanDefinition != null) {
                if (!this.allowBeanDefinitionOverriding) {
                    throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
                            "Cannot register bean definition [" + beanDefinition + "] for bean '" + beanName +
                            "': There is already [" + oldBeanDefinition + "] bound.");
                }
                else {
                    if (this.logger.isInfoEnabled()) {
                        this.logger.info("Overriding bean definition for bean '" + beanName +
                                "': replacing [" + oldBeanDefinition + "] with [" + beanDefinition + "]");
                    }
                }
            }
            else {
                // 增加beanDefinitionNames
                this.beanDefinitionNames.add(beanName);
                // 清除缓存
                this.frozenBeanDefinitionNames = null;
            }
            // 仍处于启动注册阶段
            // 注册 beanDefinitionMap 新实例 beanName + beanDefinitio
            this.beanDefinitionMap.put(beanName, beanDefinition);
        }
        if (oldBeanDefinition != null || containsSingleton(beanName)) {
            resetBeanDefinition(beanName);
        }
    }

上述代码中首先验证了beanName和BeannDefinition不可为空,然后继续校验了MethodOverridesMethodOverrides在解析并组装beanDefinition时lookup-method和recpse-method的源码中有提到，继续判断beanDefinitionMap是否存在该bean，如果bean已经存在，通过allowBeanDefinitionOverriding属性判断是否可覆盖，反之则抛出异常；如果不存在则需要判断本次是否是第一次注册bean，如果是则初始化beanDefinitionMap后进行put操作，反之直接put beanDefinitionMap完成注册；

https://blog.csdn.net/qq_30257149/article/details/87972291