Spring 源码解析（三）加载配置文件3

继续上一章，我们来分析XmlBeanDefinitionReader的loadBeanDefinitions(configLocation)方法，跟踪方法最后调用的是其父类org.springframework.beans.factory.support.AbstractBeanDefinitionReader中的loadBeanDefinitions(String location, Set<Resource> actualResources)方法

 //org.springframework.beans.factory.support.AbstractBeanDefinitionReader
 1 /**
     * Load bean definitions from the specified resource location.
     * <p>The location can also be a location pattern, provided that the
     * ResourceLoader of this bean definition reader is a ResourcePatternResolver.
     * @param location the resource location, to be loaded with the ResourceLoader
     * (or ResourcePatternResolver) of this bean definition reader
     * @param actualResources a Set to be filled with the actual Resource objects
     * that have been resolved during the loading process. May be {@code null}
     * to indicate that the caller is not interested in those Resource objects.
     * @return the number of bean definitions found
     * @throws BeanDefinitionStoreException in case of loading or parsing errors
     * @see #getResourceLoader()
     * @see #loadBeanDefinitions(org.springframework.core.io.Resource)
     * @see #loadBeanDefinitions(org.springframework.core.io.Resource[])
     */
    public int loadBeanDefinitions(String location, Set<Resource> actualResources) throws BeanDefinitionStoreException {
        ResourceLoader resourceLoader = getResourceLoader();
        if (resourceLoader == null) {
            throw new BeanDefinitionStoreException(
                    "Cannot import bean definitions from location [" + location + "]: no ResourceLoader available");
        }

        if (resourceLoader instanceof ResourcePatternResolver) {
            // Resource pattern matching available.
            try {
                Resource[] resources = ((ResourcePatternResolver) resourceLoader).getResources(location);
                int loadCount = loadBeanDefinitions(resources);
                if (actualResources != null) {
                    for (Resource resource : resources) {
                        actualResources.add(resource);
                    }
                }
                if (logger.isDebugEnabled()) {
                    logger.debug("Loaded " + loadCount + " bean definitions from location pattern [" + location + "]");
                }
                return loadCount;
            }
            catch (IOException ex) {
                throw new BeanDefinitionStoreException(
                        "Could not resolve bean definition resource pattern [" + location + "]", ex);
            }
        }
        else {
            // Can only load single resources by absolute URL.
            Resource resource = resourceLoader.getResource(location);
            int loadCount = loadBeanDefinitions(resource);
            if (actualResources != null) {
                actualResources.add(resource);
            }
            if (logger.isDebugEnabled()) {
                logger.debug("Loaded " + loadCount + " bean definitions from location [" + location + "]");
            }
            return loadCount;
        }
    }

从注释的第一句话--Load bean definitions from the specified resource location，我们就能明白这个方法做了什么事情。

第17行，获取ResourceLoader，其实就是前面创建的XmlWebApplicationContext实例。下图清楚表明了两者之间的关系

第26行，按照配置文件路径location获取Resource类型数组，实际的实现类为ServletContextResource，这个类中包装了servletContext和配置文件路径path，还提供了一些访问资源的方法。

第27行，解析了配置文件，跟踪方法，最终调用的是类中的loadBeanDefinitions(EncodedResource encodedResource)方法

 //org.springframework.beans.factory.xml.XmlBeanDefinitionReader
 1     /**
     * 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());
        }

        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 {
            InputStream inputStream = encodedResource.getResource().getInputStream();
            try {
                InputSource inputSource = new InputSource(inputStream);
                if (encodedResource.getEncoding() != null) {
                    inputSource.setEncoding(encodedResource.getEncoding());
                }
                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();
            }
        }
    }

第24行，从Resource（实际是前边创建的servletContextResource）获取输入流。

第26行，根据数据流创建InputSource。

第30行，处理InputSource，即解析配置文件，进入方法

 //org.springframework.beans.factory.xml.XmlBeanDefinitionReader
 1     /**
     * 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
     * @see #doLoadDocument
     * @see #registerBeanDefinitions
     */
    protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)
            throws BeanDefinitionStoreException {
        try {
            Document doc = doLoadDocument(inputSource, resource);
            return registerBeanDefinitions(doc, resource);
        }
            //省略catch
    }

从注释的第一行--Actually load bean definitions from the specified XML file，这个方法是真正从指定的配置文件加载bean。

第13行，将配置文件转换Document实例。

第14行，解析Document实例，进入方法

 //org.springframework.beans.factory.xml.XmlBeanDefinitionReader
 1     /**
     * 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
     */
    public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
        BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
        documentReader.setEnvironment(this.getEnvironment());
        int countBefore = getRegistry().getBeanDefinitionCount();
18         documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
        return getRegistry().getBeanDefinitionCount() - countBefore;
    }

第15行，创建BeanDefinitionDocumentReader实例（实际上是其实现类DefaultBeanDefinitionDocumentReader实例），用来解析Document。

第18行，创建了XmlReaderContext实例，调用DefaultBeanDefinitionDocumentReader的registerBeanDefinitions（）方法解析document。

我们先来总结下XmlBeanDefinitionReader的工作，下一章介绍BeanDefinitionDocumentReader如何解析document。

1、根据配置文件路径创建Resource实例（实际上是其实现类servletContextResource实例，包含了servletContext和配置文件路径path），

2、通过Resource实例创建InputSource，

3、根据InputSource、Resource创建Document，

4、创建XmlReaderContext实例，包含了Resource、ProblemReporter、EventListener 、SourceExtractor、XmlBeanDefinitionReader、NamespaceHandlerResolver，

4、创建BeanDefinitionDocumentReader实例（实际上是其实现类DefaultBeanDefinitionDocumentReader实例），

5、调用DefaultBeanDefinitionDocumentReader的registerBeanDefinitions（Document doc, XmlReaderContext readerContext）方法解析Document。