前言:上一篇讲到了Xml Bean读取器(XmlBeanDefinitionReader)调用其父类AbstractBeanDefinitionReader的reader.loadBeanDefinitions方法读取Bean定义资源,此篇我们继续后面的内容。
(5)AbstractBeanDefinitionReader的loadBeanDefinitions方法
方法源码如下:
//重载方法,调用下面的loadBeanDefinitions(String, Set<Resource>)方法 @Override public int loadBeanDefinitions(String location) throws BeanDefinitionStoreException { return loadBeanDefinitions(location, null); } public int loadBeanDefinitions(String location, @Nullable Set<Resource> actualResources) throws BeanDefinitionStoreException { //获取在IoC容器初始化过程中设置的资源加载器 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 { //将指定位置的Bean定义资源文件解析为Spring IOC容器封装的资源 //加载多个指定位置的Bean定义资源文件 Resource[] resources = ((ResourcePatternResolver) resourceLoader).getResources(location); //委派调用其子类XmlBeanDefinitionReader的方法,实现加载功能 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. //将指定位置的Bean定义资源文件解析为Spring IOC容器封装的资源 //加载单个指定位置的Bean定义资源文件 Resource resource = resourceLoader.getResource(location); //委派调用其子类XmlBeanDefinitionReader的方法,实现加载功能 int loadCount = loadBeanDefinitions(resource); if (actualResources != null) { actualResources.add(resource); } if (logger.isDebugEnabled()) { logger.debug("Loaded " + loadCount + " bean definitions from location [" + location + "]"); } return loadCount; } } //重载方法,调用loadBeanDefinitions(String); @Override public int loadBeanDefinitions(String... locations) throws BeanDefinitionStoreException { Assert.notNull(locations, "Location array must not be null"); int counter = 0; for (String location : locations) { counter += loadBeanDefinitions(location); } return counter; }
loadBeanDefinitions(Resource...resources)样也是调用XmlBeanDefinitionReader的loadBeanDefinitions方法。
对AbstractBeanDefinitionReader的loadBeanDefinitions方法源码分析可以看出该方法:
首先,调用资源加载器的获取资源方法resourceLoader.getResource(location),获取到要加载的资源;
其次,真正执行加载功能是其子类XmlBeanDefinitionReader的loadBeanDefinitions方法。
(6)资源加载器获取要读入的资源
AbstractBeanDefinitionReader通过调用其父类DefaultResourceLoader的getResource方法获取要加载的资源,源码如下:
//获取Resource的具体实现方法 @Override public Resource getResource(String location) { Assert.notNull(location, "Location must not be null"); for (ProtocolResolver protocolResolver : this.protocolResolvers) { Resource resource = protocolResolver.resolve(location, this); if (resource != null) { return resource; } } //如果是类路径的方式,需要使用ClassPathResource来得到bean文件的资源对象 if (location.startsWith("/")) { return getResourceByPath(location); } else if (location.startsWith(CLASSPATH_URL_PREFIX)) { return new ClassPathResource(location.substring(CLASSPATH_URL_PREFIX.length()), getClassLoader()); } else { try { // Try to parse the location as a URL... // 如果是URL方式,使用UrlResource作为bean文件的资源对象 URL url = new URL(location); return (ResourceUtils.isFileURL(url) ? new FileUrlResource(url) : new UrlResource(url)); } catch (MalformedURLException ex) { // No URL -> resolve as resource path. //如果既不是classpath标识,又不是URL标识的Resource定位,则调用容器本身的getResourceByPath方法获取Resource return getResourceByPath(location); } } }
FileSystemXmlApplicationContext容器提供了getResourceByPath方法的实现,就是为了处理既不是classpath 标识,又不是URL标识的Resource定位这种情况。
@Override protected Resource getResourceByPath(String path) { if (path.startsWith("/")) { path = path.substring(1); } //这里使用文件系统资源对象来定义bean文件 return new FileSystemResource(path); }
这样代码就回到了FileSystemXmlApplicationContext中来,他提供了FileSystemResource来完成从文件系统得到配置文件的资源定义。 这样就可以从文件系统路径上对IOC配置文件进行加载,当然也可以按照这个逻辑从任何地方加载,在Spring中可以看到它提供的各种资源抽象, 比如ClassPathResource、URLResource、FileSystemResource等来供我们使用。上面是定位Resource的一个过程,这只是加载过程的一部分.
(7)XmlBeanDefinitionReader加载Bean定义资源
回到XmlBeanDefinitionReader的loadBeanDefinitions(Resource …)方法看到代表bean文件的资源定义以后的载入过程。
//XmlBeanDefinitionReader加载资源的入口方法 @Override public int loadBeanDefinitions(Resource resource) throws BeanDefinitionStoreException { //将读入的XML资源进行特殊编码处理 return loadBeanDefinitions(new EncodedResource(resource)); } //这里是载入XML形式Bean定义资源文件方法 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<>(4); this.resourcesCurrentlyBeingLoaded.set(currentResources); } if (!currentResources.add(encodedResource)) { throw new BeanDefinitionStoreException( "Detected cyclic loading of " + encodedResource + " - check your import definitions!"); } try { //将资源文件转为InputStream的IO流 InputStream inputStream = encodedResource.getResource().getInputStream(); try { //从InputStream中得到XML的解析源 InputSource inputSource = new InputSource(inputStream); if (encodedResource.getEncoding() != null) { inputSource.setEncoding(encodedResource.getEncoding()); } //这里是具体的读取过程 return doLoadBeanDefinitions(inputSource, encodedResource.getResource()); } finally { //关闭从Resource中得到的IO流 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(); } } } //从特定XML文件中实际载入Bean定义资源的方法 protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource) throws BeanDefinitionStoreException { try { //将XML文件转换为DOM对象,解析过程由documentLoader实现 Document doc = doLoadDocument(inputSource, resource); //这里是启动对Bean定义解析的详细过程,该解析过程会用到Spring的Bean配置规则 return registerBeanDefinitions(doc, resource); } ... }
通过源码分析,载入Bean定义资源文件的最后一步是将Bean定义资源转换为Document对象,该过程由documentLoader实现。
(8)DocumentLoader将Bean定义资源转换为Document对象
源码如下:
//使用标准的JAXP将载入的Bean定义资源转换成document对象 @Override public Document loadDocument(InputSource inputSource, EntityResolver entityResolver, ErrorHandler errorHandler, int validationMode, boolean namespaceAware) throws Exception { //创建文件解析器工厂 DocumentBuilderFactory factory = createDocumentBuilderFactory(validationMode, namespaceAware); if (logger.isDebugEnabled()) { logger.debug("Using JAXP provider [" + factory.getClass().getName() + "]"); } //创建文档解析器 DocumentBuilder builder = createDocumentBuilder(factory, entityResolver, errorHandler); //解析Spring的Bean定义资源 return builder.parse(inputSource);} protected DocumentBuilderFactory createDocumentBuilderFactory(int validationMode, boolean namespaceAware) throws ParserConfigurationException { //创建文档解析工厂 DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance(); factory.setNamespaceAware(namespaceAware); //设置解析XML的校验 if (validationMode != XmlValidationModeDetector.VALIDATION_NONE) { factory.setValidating(true); if (validationMode == XmlValidationModeDetector.VALIDATION_XSD) { // Enforce namespace aware for XSD... factory.setNamespaceAware(true); try { factory.setAttribute(SCHEMA_LANGUAGE_ATTRIBUTE, XSD_SCHEMA_LANGUAGE); } catch (IllegalArgumentException ex) { ParserConfigurationException pcex = new ParserConfigurationException( "Unable to validate using XSD: Your JAXP provider [" + factory + "] does not support XML Schema. Are you running on Java 1.4 with Apache Crimson? " + "Upgrade to Apache Xerces (or Java 1.5) for full XSD support."); pcex.initCause(ex); throw pcex; } } } return factory; }
该解析过程调用JavaEE标准的JAXP标准进行处理。至此Spring IOC容器根据定位的Bean定义资源文件,将其加载读入并转换成为Document对象过程完成。
接下来继续分析Spring IOC容器将载入的Bean定义资源文件转换为Document对象之后,是如何将其解析为Spring IOC管理的Bean对象并将其注册到容器中的。
IOC容器初始化内容较多,分了几篇来写,此为第二篇,欢迎关注其余内容,感谢!