parseDefaultElement下的四种获取element方法

1、import引用

2、alias别名

3、bean

4、beans

import

protected void importBeanDefinitionResource(Element ele) {
		String location = ele.getAttribute(RESOURCE_ATTRIBUTE);
		if (!StringUtils.hasText(location)) {
			getReaderContext().error("Resource location must not be empty", ele);
			return;
		}

		// Resolve system properties: e.g. "${user.dir}"
		location = getReaderContext().getEnvironment().resolveRequiredPlaceholders(location);

		Set<Resource> actualResources = new LinkedHashSet<>(4);

		// Discover whether the location is an absolute or relative URI
		boolean absoluteLocation = false;
		try {
			absoluteLocation = ResourcePatternUtils.isUrl(location) || ResourceUtils.toURI(location).isAbsolute();
		}
		catch (URISyntaxException ex) {
			// cannot convert to an URI, considering the location relative
			// unless it is the well-known Spring prefix "classpath*:"
		}

		// Absolute or relative?
		if (absoluteLocation) {
			try {
				int importCount = getReaderContext().getReader().loadBeanDefinitions(location, actualResources);
				if (logger.isTraceEnabled()) {
					logger.trace("Imported " + importCount + " bean definitions from URL location [" + location + "]");
				}
			}
			catch (BeanDefinitionStoreException ex) {
				getReaderContext().error(
						"Failed to import bean definitions from URL location [" + location + "]", ele, ex);
			}
		}
		else {
			// No URL -> considering resource location as relative to the current file.
			try {
				int importCount;
				Resource relativeResource = getReaderContext().getResource().createRelative(location);
				if (relativeResource.exists()) {
					importCount = getReaderContext().getReader().loadBeanDefinitions(relativeResource);
					actualResources.add(relativeResource);
				}
				else {
					String baseLocation = getReaderContext().getResource().getURL().toString();
					importCount = getReaderContext().getReader().loadBeanDefinitions(
							StringUtils.applyRelativePath(baseLocation, location), actualResources);
				}
				if (logger.isTraceEnabled()) {
					logger.trace("Imported " + importCount + " bean definitions from relative location [" + location + "]");
				}
			}
			catch (IOException ex) {
				getReaderContext().error("Failed to resolve current resource location", ele, ex);
			}
			catch (BeanDefinitionStoreException ex) {
				getReaderContext().error(
						"Failed to import bean definitions from relative location [" + location + "]", ele, ex);
			}
		}
		Resource[] actResArray = actualResources.toArray(new Resource[0]);
		getReaderContext().fireImportProcessed(location, actResArray, extractSource(ele));
	}

1、先判断系统属性

2、判断是否绝对路径

涉及方法isUrl，toURI的isAbsolute()

isUrl 判断 a、前缀classpath*:

b、或者classpath:

c、或者可实例化URL对象

b，c判断的子方法，这里try 是否能实例对象进行判断有点意思，代码如下：

	public static boolean isUrl(@Nullable String resourceLocation) {
		if (resourceLocation == null) {
			return false;
		}
		if (resourceLocation.startsWith(CLASSPATH_URL_PREFIX)) {
			return true;
		}
		try {
			new URL(resourceLocation);
			return true;
		}
		catch (MalformedURLException ex) {
			return false;
		}
	}

3、分别对绝对路径和相对路径进行处理

	public int loadBeanDefinitions(String location, @Nullable Set<Resource> actualResources) throws BeanDefinitionStoreException {
		ResourceLoader resourceLoader = getResourceLoader();
		if (resourceLoader == null) {
			throw new BeanDefinitionStoreException(
					"Cannot load bean definitions from location [" + location + "]: no ResourceLoader available");
		}

		if (resourceLoader instanceof ResourcePatternResolver) {
			// Resource pattern matching available.
			try {
				Resource[] resources = ((ResourcePatternResolver) resourceLoader).getResources(location);
				//这里眼熟不？开始递归获取beanDefinitions了
				int count = loadBeanDefinitions(resources);
				if (actualResources != null) {
					Collections.addAll(actualResources, resources);
				}
				if (logger.isTraceEnabled()) {
					logger.trace("Loaded " + count + " bean definitions from location pattern [" + location + "]");
				}
				return count;
			}
			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 count = loadBeanDefinitions(resource);
			if (actualResources != null) {
				actualResources.add(resource);
			}
			if (logger.isTraceEnabled()) {
				logger.trace("Loaded " + count + " bean definitions from location [" + location + "]");
			}
			return count;
		}
	}

思路很简单，根据路径，用对应的loader解析出来resource，然后actualResources用于存储resource对象数组；相对路径的也是大同小异

先用org.springframework.core.io.Resource#createRelative判断相对路径下是否有resource，有的话加入；没有获取base路径，拼上相对路径，用绝对路径的方式加载

4、最后org.springframework.beans.factory.parsing.ReaderContext#fireImportProcessed(java.lang.String, org.springframework.core.io.Resource[], java.lang.Object)方法将之前获得的actualResources数组进行处理