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导读:

XmlBeanFactory继承自DefaultListableBeanFactory,扩展了从xml文档中读取bean definition的能力。从本质上讲,XmlBeanFactory等同于DefaultListableBeanFactory+XmlBeanDefinitionReader ,如果有更好的需求,可以考虑使用DefaultListableBeanFactory+XmlBeanDefinitionReader方案,因为该方案可以从多个xml文件读取资源,并且在解析xml上具有更灵活的可配置性。

1 XmlBeanFactory的使用

典型构造方法:

    public XmlBeanFactory(Resource resource, BeanFactory parentBeanFactory) throws BeansException {
        super(parentBeanFactory);
        this.reader.loadBeanDefinitions(resource);
    }

其中,

reader是XmlBeanDefinitionReader的实例,XmlBeanDefinitionReader继承自AbstractBeanDefinitionReader(http://www.cnblogs.com/davidwang456/p/4190428.html 已经介绍过)。

 Resource 接口封装了各种可能的资源类型,也就是对使用者来说屏蔽了文件类型的不同。这样所有的资源都被可以通过 InputStream 这个类来获取,所以也屏蔽了资源的提供者。另外还有一个问题就是加载资源的问题,也就是资源的加载者要统一,从上图中可以看出这个任务是由 ResourceLoader 接口完成,他屏蔽了所有的资源加载者的差异,只需要实现这个接口就可以加载所有的资源,他的默认实现是 DefaultResourceLoader。

 1.1 Resource 接口继承了 InputStreamSource 接口,这个接口中有个 getInputStream 方法,返回的是 InputStream 类。

public interface InputStreamSource {
    InputStream getInputStream() throws IOException;
}
getInputStream设计希望每次请求都返回一个新的流。这种要求在一个场合非常重要,例如javamail api,它在创建多个邮件附件时需要多次读取到流,在这中情况下,它就要求每个getInputStream请求能返回一个新的流。

1.2 抽象资源类AbstractResource继承自Source接口,实现了部分方法。
exists方法检查一个文件或者输入量是否可以打开;
isOpen 通常返回false;
  getUrl和getFile 抛出异常;
toString返回描述信息。

另外有一个有用的方法:lastModified()返回文件的最后修改时间。调用了File.lastModified() 返回此抽象路径名表示的文件最后一次被修改的时间。
    @Override
    public long lastModified() throws IOException {
        long lastModified = getFileForLastModifiedCheck().lastModified();
        if (lastModified == 0L) {
            throw new FileNotFoundException(getDescription() +
                    " cannot be resolved in the file system for resolving its last-modified timestamp");
        }
        return lastModified;
    }

1.3 Resource的实现子类:

AbstractResource的直接子类有:AbstractFileResolvingResource, ByteArrayResource,BeanDefinitionResource, DescriptiveResource, FileSystemResource, InputStreamResource, PathResource, VfsResource。
其中,AbstractFileResolvingResource的直接子类有:ClassPathResource, PortletContextResource, ServletContextResource, UrlResource
比较重要的实现类为实现了ContextResource接口的资源类,ContextResource接口继承了Resource接口,通过从一个封装的context中加载资源来扩展Resource接口的功能。例如:可以从ServletContext,PortletContext,普通的classpth路径或者文件系统的相对路径(特别是没有指明前缀,因此适用于本地ResourceLoader的context),其子类实现有:PortletContextResource, ServletContextResource,ClassPathContextResource,ClassRelativeContextResource,FileSystemContextResource.

1.4 资源的加载ResourceLoader,ResourceLoader是一个加载资源的策略接口,可以从classpth或者文件系统中,ApplicationContext需要加载资源功能,使用了其扩展类ResourcePatternReolver。DefaultResourceLoader是该接口的标准实现,适用于一个ApplicationContext外部,可以用在ResourceEditor中。在application允许过程中,使用特定的context子原因加载策略,可以将type资源和资源组通过string的形式设置bean的属性。

(来源:http://www.ibm.com/developerworks/cn/java/j-lo-spring-principle/)

2. Bean的解析与注册详细过程分析

    (来源:http://www.ibm.com/developerworks/cn/java/j-lo-spring-principle/)

   首先, XmlBeanFactory构造函数this.reader.loadBeanDefinitions(resource);

  1. XmlBeanDefinitionReader加载bean定义:loadBeanDefinitions方法

    2. XmlBeanDefinitionReader解析bean定义,并注册:doLoadBeanDefinitions方法

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

  3.1. 使用标准的JAXP配置的xml解析器从Resource中加载到Document。

    /**
     * Load the {@link Document} at the supplied {@link InputSource} using the standard JAXP-configured
     * XML parser.
     */
    @Override
    public Document loadDocument(InputSource inputSource, EntityResolver entityResolver,
            ErrorHandler errorHandler, int validationMode, boolean namespaceAware) throws Exception {

        DocumentBuilderFactory factory = createDocumentBuilderFactory(validationMode, namespaceAware);
        if (logger.isDebugEnabled()) {
            logger.debug("Using JAXP provider [" + factory.getClass().getName() + "]");
        }
        DocumentBuilder builder = createDocumentBuilder(factory, entityResolver, errorHandler);
        return builder.parse(inputSource);
    }

   3.2.根据加载的Document 注册Bean definition。

    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;
    }

3.2.1 创建BeanDefinitionDocument的解析器BeanUtils.instantiateClass(this.documentReaderClass)

3.2.2 BeanDefinitionDocument解析器注册bean definition,从根节点<beans>开始

    /**
     * Register each bean definition within the given root {@code <beans/>} element.
     */
    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);

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

        this.delegate = parent;
    }
/**
     * 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)) {
                        parseDefaultElement(ele, delegate);
                    }
                    else {
                        delegate.parseCustomElement(ele);
                    }
                }
            }
        }
        else {
            delegate.parseCustomElement(root);
        }
    }

    private void parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate) {
        if (delegate.nodeNameEquals(ele, IMPORT_ELEMENT)) {
            importBeanDefinitionResource(ele);
        }
        else if (delegate.nodeNameEquals(ele, ALIAS_ELEMENT)) {
            processAliasRegistration(ele);
        }
        else if (delegate.nodeNameEquals(ele, BEAN_ELEMENT)) {
            processBeanDefinition(ele, delegate);
        }
        else if (delegate.nodeNameEquals(ele, NESTED_BEANS_ELEMENT)) {
            // recurse
            doRegisterBeanDefinitions(ele);
        }
    }

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

    public XmlReaderContext createReaderContext(Resource resource) {
        return new XmlReaderContext(resource, this.problemReporter, this.eventListener,
                this.sourceExtractor, this, getNamespaceHandlerResolver());
    }

5.调用:

    protected NamespaceHandlerResolver createDefaultNamespaceHandlerResolver() {
        return new DefaultNamespaceHandlerResolver(getResourceLoader().getClassLoader());
    }

6.BeanDefinitionReaderUtils.registerBeanDefinition

    /**
     * Process the given bean element, parsing the bean definition
     * and registering it with the registry.
     */
    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));
        }
    }

7.处理给定的Bean元素,并解析到BeanDefinition。

    /**
     * Process the given bean element, parsing the bean definition
     * and registering it with the registry.
     */
    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));
        }
    }

8.

    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 aliase : aliases) {
                registry.registerAlias(beanName, aliase);
            }
        }
    }

9.将解析的Bean定义放入BeanDefinitionNames和BeanDefinitionMap保存已经aliasMap等

    @Override
    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 {
                ((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 (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.frozenBeanDefinitionNames = null;
            }
            this.beanDefinitionMap.put(beanName, beanDefinition);
        }

        if (oldBeanDefinition != null || containsSingleton(beanName)) {
            resetBeanDefinition(beanName);
        }
    }

 

3. 一个非常重要的部分就是建立 Bean 对象实例之间的关系,这也是 Spring 框架的核心竞争力,何时、如何建立他们之间的关系请看下面的时序图:

    来源:http://www.ibm.com/developerworks/cn/java/j-lo-spring-principle/

4. 小结:

  从spring 3.1版本后,xmlBeanFactory被表明为Deprecated. 推荐使用DefaultListableBeanFactory和XmlBeanDefinitionReader替换。

本文从xmlBeanFactory扩展到XmlBeanDefinitionReader,再到Resource接口。

一些情节还没有理顺,显得有些杂乱,后续会修改(写的很累,休整一下)。写这篇博客的时候,这句话一直在我脑边回想:

"写书就像冒险。一开始它是玩具和娱乐。然后她成了你的情妇。然后是你的主人。然后变成一个暴君。最后你终于认命的时候,它死了,然后给拖到外面游街。" ----温斯顿.丘吉尔

参考文献:

1. http://www.ibm.com/developerworks/cn/java/j-lo-spring-principle/

 

posted on 2015-01-08 11:19  一天不进步,就是退步  阅读(9313)  评论(0编辑  收藏