在spring中，如果你想创建容器少不了使用常见的xmlbeanfactory，ClassPathXmlApplicationContext，FileSystemXmlApplicationContext，在这里，不介绍后两者。即使xmlbeanfactory已经过时了，但是有必要还是说一说。创建容器的代码：BeanFactory bf = new XmlBeanFactory(new ClassPathResource("applicationContextIOC.xml"))；发现这里的构造函数中的参数是ClassPathResource类，这个类的作用就是加载配置文件，也就是说spring的配置文件的加载少不了这个类。这个类它是怎样加载文件的，我们一起追踪它的执行流程。
Resource是ClassPathResource实现的接口，Resource继承了InputStreamSource接口。在InputStreamSource这个接口里面只有一个方法，一起来看一下。
这说明拿到了输入流，这样我们就可以对文件做操作。此时，Resource接口有这些方法。
足以说明Resource接口封装底层资源，这些方法这里不过多介绍了。其中，exists，isReadable，isOpen是判断当前资源状态的方法。通过以上完成了对配置文件的封装，接下来介绍XmlBeanFactory的初始化过程。XmlBeanFactory类的构造函数有这样几个：
这里使用构造函数参数为Resource，进入这个方法后，看到这样的一串代码
我们点进去this(resource,null)，调用的是XmlBeanFactory(Resource, BeanFactory)这个构造函数。
通过追踪super(parentBeanFactory);可以猜到使用ignoreDependencyInterface忽略了给定接口的自动装配功能。源码如下：
在XmlBeanFactory构造函数中，资源加载的核心代码是：this.reader.loadBeanDefinitions(resource)；资源加载完成之后，接下来就是读取，在XmlBeanFactory构造函数中调用了this.reader.loadBeanDefinitions(resource)；再一次追踪一下这串代码：
可以大致猜到以上代码主要作用对资源文件的编码进行处理，追踪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());
} 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();
}
}
}
以上源码中，红色才是核心所在。追踪此代码：
/**
* 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);
}
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);
}
}
以上代码其实就是要拿到Document，通过Document注册Bean信息。再一次追踪源代码：
/**
* 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();
int countBefore = getRegistry().getBeanDefinitionCount();
documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
return getRegistry().getBeanDefinitionCount() - countBefore;
}
追踪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.
*/
@Override
public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) {
this.readerContext = readerContext;
logger.debug("Loading bean definitions");
Element root = doc.getDocumentElement();
doRegisterBeanDefinitions(root);
}
最后一句代码doRegisterBeanDefinitions(root)；开始进行对XML解析，核心源码有必要给大家看一下：
/**
* Register each bean definition within the given root {@code <beans/>} element.
*/
protected void doRegisterBeanDefinitions(Element root) {
// 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(getReaderContext(), root, parent); if (this.delegate.isDefaultNamespace(root)) {
String profileSpec = root.getAttribute(PROFILE_ATTRIBUTE);
if (StringUtils.hasText(profileSpec)) {
String[] specifiedProfiles = StringUtils.tokenizeToStringArray(
profileSpec, BeanDefinitionParserDelegate.MULTI_VALUE_ATTRIBUTE_DELIMITERS);
if (!getReaderContext().getEnvironment().acceptsProfiles(specifiedProfiles)) {
return;
}
}
} preProcessXml(root);
parseBeanDefinitions(root, this.delegate);
postProcessXml(root); this.delegate = parent;
}
解析并注册BeanDefinitions，源代码如下：
/**
* 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);
}
}
到此，整个过程才结束。经过这样的漫长的过程的学习，理解设计的思路，这样才能对spring有更好的理解与看法。希望大家给出宝贵建议，我们一起探讨，一起进步。感谢大家的支持，你的支持是我最大的动力。