原文：http://blog.csdn.net/fuliangliang/archive/2006/12/22/1454382.aspx

首先从WEB.XML入手

==>web.xml

代码 <context-param> <param-name>webAppRootKey</param-name> <param-value>task.root</param-value> </context-param>

<!-- 定义SPRING配置文件 -->

<context-param> <param-name>contextConfigLocation</param-name> <param-value>/WEB-INF/taskContext*.xml</param-value> </context-param> </span> <context-param> <param-name>log4jConfigLocation</param-name> <param-value>/WEB-INF/log4j.properties</param-value> </context-param> <!-- 定义LOG4J监听器 --> <listener> <listener-class>org.springframework.web.util.Log4jConfigListener</listener-class> </listener>

<!-- 定义SPRING监听器 -->

<listener> <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class> </listener>

进入contextLoaderListener看看到底加载时做了甚么 ==>org.springframework.web.context.ContextLoaderListener

代码 public class ContextLoaderListener implements ServletContextListener {

private ContextLoader contextLoader;

/**

• Initialize the root web application context. */ //当WEB上下文初始化时,系统会调用此方法
  public void contextInitialized(ServletContextEvent event) {
  this.contextLoader = createContextLoader();

//监听到WEB上下文初始化的时候执行SPRING上下文contextLoader的初始化工作
this.contextLoader.initWebApplicationContext(event.getServletContext());

}

/**

• Create the ContextLoader to use. Can be overridden in subclasses.
• @return the new ContextLoader */ protected ContextLoader createContextLoader() {
  return new ContextLoader();
  }

/**

• Return the ContextLoader used by this listener. */ public ContextLoader getContextLoader() {
  return contextLoader;
  }

/**

• Close the root web application context. */ public void contextDestroyed(ServletContextEvent event) {
  if (this.contextLoader != null) {
  this.contextLoader.closeWebApplicationContext(event.getServletContext());
  }
  }

}

看一下是怎么来初始化webapplicationContext的 ==>contextLoader.initWebApplicationContext

代码 public WebApplicationContext initWebApplicationContext(ServletContext servletContext)
throws IllegalStateException, BeansException {

if (servletContext.getAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE) != null) {  throw new IllegalStateException(  "Cannot initialize context because there is already a root application context

present - " +
"check whether you have multiple ContextLoader* definitions in your web.xml!");
}

long startTime = System.currentTimeMillis();
if (logger.isInfoEnabled()) {  logger.info("Root WebApplicationContext: initialization started");
}
servletContext.log("Loading Spring root WebApplicationContext");  try {  // Determine parent for root web application context, if any.  ApplicationContext parent = loadParentContext(servletContext);  // Store context in local instance variable, to guarantee that  // it is available on ServletContext shutdown.  //创建web上下文  this.context = createWebApplicationContext(servletContext, parent);  servletContext.setAttribute(  WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, this.context);   if (logger.isInfoEnabled()) {  logger.info("Using context class [" + this.context.getClass().getName() +  "] for root WebApplicationContext");  }  if (logger.isDebugEnabled()) {  logger.debug("Published root WebApplicationContext [" + this.context +  "] as ServletContext attribute with name [" +  WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE + "]");  }  if (logger.isInfoEnabled()) {  long elapsedTime = System.currentTimeMillis() - startTime;  logger.info("Root WebApplicationContext: initialization completed in " + elapsedTime + "

ms");
}

  return this.context;
}
catch (RuntimeException ex) {  logger.error("Context initialization failed", ex);  servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, ex);  throw ex;
}
catch (Error err) {  logger.error("Context initialization failed", err);  servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, err);  throw err;
}

}

==>contextLoader.createWebApplicationContext(servletContext, parent);

代码 protected WebApplicationContext createWebApplicationContext(
ServletContext servletContext, ApplicationContext parent) throws BeansException {
//根据servletContext来决定要实例化的WebApplicationContext
Class contextClass = determineContextClass(servletContext);
if (!ConfigurableWebApplicationContext.class.isAssignableFrom(contextClass)) {
throw new ApplicationContextException("Custom context class [" + contextClass.getName() +
"] is not of type ConfigurableWebApplicationContext");
}
ConfigurableWebApplicationContext wac =
(ConfigurableWebApplicationContext) BeanUtils.instantiateClass(contextClass);
wac.setParent(parent);
wac.setServletContext(servletContext);

//得到WEB.XML中设置的SPRING配置文件位置
String configLocation = servletContext.getInitParameter(CONFIG_LOCATION_PARAM);
if (configLocation != null) {  //把配置文件分段后设置到WebApplicationContext的ConfigLocations中  wac.setConfigLocations(StringUtils.tokenizeToStringArray(configLocation,  ConfigurableWebApplicationContext.CONFIG_LOCATION_DELIMITERS));
}
//刷新WebApplicationContext
wac.refresh();
return wac;

}

==>contextLoader.determineContextClass(servletContext);

代码 protected Class determineContextClass(ServletContext servletContext) throws ApplicationContextException {
//获得需要实例化的CONTEXT类名,在web.xml中有设置,如果没有设置,那么为空
String contextClassName = servletContext.getInitParameter(CONTEXT_CLASS_PARAM);
if (contextClassName != null) {
try {
return ClassUtils.forName(contextClassName);
}
catch (ClassNotFoundException ex) {
throw new ApplicationContextException(
"Failed to load custom context class [" + contextClassName + "]", ex);
}
}
//如果在spring web.xml中没有设置context类位置,那么取得默认context
else {
//取得defaultStrategies配置文件中的WebApplicationContext属性
contextClassName = defaultStrategies.getProperty(WebApplicationContext.class.getName());
try {
return ClassUtils.forName(contextClassName);
}
catch (ClassNotFoundException ex) {
throw new ApplicationContextException(
"Failed to load default context class [" + contextClassName + "]", ex);
}
}
}

SPRING上下文默认的策略是甚么呢? ==>contextLoader.defaultStrategies

代码 private static final Properties defaultStrategies;

static {
// Load default strategy implementations from properties file.
// This is currently strictly internal and not meant to be customized
// by application developers.
try {
//设置classpath为contextLoader同级目录
ClassPathResource resource = new ClassPathResource(DEFAULT_STRATEGIES_PATH, ContextLoader.class);
//加载该目录下的所有properties文件
defaultStrategies = PropertiesLoaderUtils.loadProperties(resource);
}
catch (IOException ex) {
throw new IllegalStateException("Could not load 'ContextLoader.properties': " + ex.getMessage());
}
}

找到同级目录下的配置文件 ==>ContextLoader.properties

代码

Default WebApplicationContext implementation class for ContextLoader.

Used as fallback when no explicit context implementation has been specified as context-param.

Not meant to be customized by application developers.

#默认的WebApplicationContext为org.springframework.web.context.support.XmlWebApplicationContext
org.springframework.web.context.WebApplicationContext=org.springframework.web.context.support.XmlWebApplicationContext

==>org.springframework.web.context.support.XmlWebApplicationContext

代码 public class XmlWebApplicationContext extends AbstractRefreshableWebApplicationContext {

/** Default config location for the root context */

//配置了默认的spring配置文件
public static final String DEFAULT_CONFIG_LOCATION = "/WEB-INF/applicationContext.xml";

//配置文件默认BUILD路径
public static final String DEFAULT_CONFIG_LOCATION_PREFIX = "/WEB-INF/";

//配置文件默认后缀名
public static final String DEFAULT_CONFIG_LOCATION_SUFFIX = ".xml";

/**

• Loads the bean definitions via an XmlBeanDefinitionReader.
• @see org.springframework.beans.factory.xml.XmlBeanDefinitionReader
• @see #initBeanDefinitionReader
• @see #loadBeanDefinitions */ //获得bean配置
  protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws IOException {
  //从BEAN工厂获得一个XmlBeanDefinitionReader 来读取SPRING配置文件
  XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);

//设置beanDefinitionReader服务于当前CONTEXT
// resource loading environment.
beanDefinitionReader.setResourceLoader(this);
beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this));  // Allow a subclass to provide custom initialization of the reader,
// then proceed with actually loading the bean definitions.
initBeanDefinitionReader(beanDefinitionReader);
//读取配置文件
loadBeanDefinitions(beanDefinitionReader);

}

/**

• Initialize the bean definition reader used for loading the bean
• definitions of this context. Default implementation is empty.

• <p>Can be overridden in subclasses, e.g. for turning off XML validation

• or using a different XmlBeanDefinitionParser implementation.
• @param beanDefinitionReader the bean definition reader used by this context
• @see org.springframework.beans.factory.xml.XmlBeanDefinitionReader#setValidationMode
• @see org.springframework.beans.factory.xml.XmlBeanDefinitionReader#setDocumentReaderClass */ protected void initBeanDefinitionReader(XmlBeanDefinitionReader beanDefinitionReader) {
  }

/**

• Load the bean definitions with the given XmlBeanDefinitionReader.

• <p>The lifecycle of the bean factory is handled by the refreshBeanFactory method;

• therefore this method is just supposed to load and/or register bean definitions.

• <p>Delegates to a ResourcePatternResolver for resolving location patterns

• into Resource instances.
• @throws org.springframework.beans.BeansException in case of bean registration errors
• @throws java.io.IOException if the required XML document isn't found
• @see #refreshBeanFactory
• @see #getConfigLocations
• @see #getResources
• @see #getResourcePatternResolver */ //读取配置文件
  protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws BeansException, IOException {
  String[] configLocations = getConfigLocations();
  if (configLocations != null) {
  for (int i = 0; i < configLocations.length; i++) {
  reader.loadBeanDefinitions(configLocations[i]);
  }
  }
  }

/**

• The default location for the root context is "/WEB-INF/applicationContext.xml",
• and "/WEB-INF/test-servlet.xml" for a context with the namespace "test-servlet"
• (like for a DispatcherServlet instance with the servlet-name "test"). */ //获得默认的ConfigLocations
  protected String[] getDefaultConfigLocations() {
  if (getNamespace() != null) {
  return new String[] {DEFAULT_CONFIG_LOCATION_PREFIX + getNamespace() +

DEFAULT_CONFIG_LOCATION_SUFFIX};
}
else {
return new String[] {DEFAULT_CONFIG_LOCATION};
}
}

==>AbstractBeanDefinitionReader.loadBeanDefinitions()

代码 public int loadBeanDefinitions(String location) 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 {

//根据配置文件读取相应配置
Resource[] resources = ((ResourcePatternResolver) resourceLoader).getResources(location);
int loadCount = loadBeanDefinitions(resources);
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 (logger.isDebugEnabled()) {
logger.debug("Loaded " + loadCount + " bean definitions from location [" + location + "]");
}
return loadCount;
}
}

这个是其中一个ResourceLoader的实现 ==>PathMatchingResourcePatternResolver.getResources(String locationPattern);

代码 public Resource[] getResources(String locationPattern) throws IOException {
Assert.notNull(locationPattern, "Location pattern must not be null");
if (locationPattern.startsWith(CLASSPATH_ALL_URL_PREFIX)) {
// a class path resource (multiple resources for same name possible)

  if (getPathMatcher().isPattern(locationPattern.substring(CLASSPATH_ALL_URL_PREFIX.length()))) {  // a class path resource pattern  return findPathMatchingResources(locationPattern);  }  else {  // all class path resources with the given name  return findAllClassPathResources(locationPattern.substring(CLASSPATH_ALL_URL_PREFIX.length()));  }
}
else {  // Only look for a pattern after a prefix here  // (to not get fooled by a pattern symbol in a strange prefix).  int prefixEnd = locationPattern.indexOf(":") + 1;  if (getPathMatcher().isPattern(locationPattern.substring(prefixEnd))) {  // a file pattern  return findPathMatchingResources(locationPattern);  }  else {  // a single resource with the given name  return new Resource[] {getResourceLoader().getResource(locationPattern)};  }
}

}

==>PathMatchingResourcePatternResolver.findPathMatchingResources(String locationPattern);

代码 protected Resource[] findPathMatchingResources(String locationPattern) throws IOException {
String rootDirPath = determineRootDir(locationPattern);
String subPattern = locationPattern.substring(rootDirPath.length());
Resource[] rootDirResources = getResources(rootDirPath);
//collectionFactory初始化一个set容量为16
Set result = CollectionFactory.createLinkedSetIfPossible(16);
for (int i = 0; i < rootDirResources.length; i++) {
Resource rootDirResource = rootDirResources[i];
if (isJarResource(rootDirResource)) {
result.addAll(doFindPathMatchingJarResources(rootDirResource, subPattern));
}
else {
result.addAll(doFindPathMatchingFileResources(rootDirResource, subPattern));
}
}
if (logger.isDebugEnabled()) {
logger.debug("Resolved location pattern [" + locationPattern + "] to resources " + result);
}
return (Resource[]) result.toArray(new Resource[result.size()]);
}

前面说到有一个刷新WebApplicationContext的操作,但是XmlWebApplicationContext 并没有实现refresh方法,而方法的实现写在

AbstractRefreshableWebApplicationContext 中

==>AbstractRefreshableWebApplicationContext.refresh();

代码 public void refresh() throws BeansException {
if (ObjectUtils.isEmpty(getConfigLocations())) {
//设置configLocations为默认的getDefaultConfigLocations()
setConfigLocations(getDefaultConfigLocations());
}
super.refresh();
}

==>AbstractApplicationContext.refresh();

代码 public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
this.startupTime = System.currentTimeMillis();

  synchronized (this.activeMonitor) {  this.active = true;  }  // Tell subclass to refresh the internal bean factory.  refreshBeanFactory();  ConfigurableListableBeanFactory beanFactory = getBeanFactory();  // Tell the internal bean factory to use the context's class loader.  beanFactory.setBeanClassLoader(getClassLoader());  // Populate the bean factory with context-specific resource editors.  beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this));  // Configure the bean factory with context semantics.  beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));  beanFactory.ignoreDependencyInterface(ResourceLoaderAware.class);  beanFactory.ignoreDependencyInterface(ApplicationEventPublisherAware.class);  beanFactory.ignoreDependencyInterface(MessageSourceAware.class);  beanFactory.ignoreDependencyInterface(ApplicationContextAware.class);  // Allows post-processing of the bean factory in context subclasses.  postProcessBeanFactory(beanFactory);  // Invoke factory processors registered with the context instance.  for (Iterator it = getBeanFactoryPostProcessors().iterator(); it.hasNext();) {  BeanFactoryPostProcessor factoryProcessor = (BeanFactoryPostProcessor) it.next();  factoryProcessor.postProcessBeanFactory(beanFactory);  }  if (logger.isInfoEnabled()) {  if (getBeanDefinitionCount() == 0) {  logger.info("No beans defined in application context [" + getDisplayName() + "]");  }  else {  logger.info(getBeanDefinitionCount() + " beans defined in application context [" +

getDisplayName() + "]");
}
}

  try {  // Invoke factory processors registered as beans in the context.  invokeBeanFactoryPostProcessors();  // Register bean processors that intercept bean creation.  registerBeanPostProcessors();  // Initialize message source for this context.  initMessageSource();  // Initialize event multicaster for this context.  initApplicationEventMulticaster();  // Initialize other special beans in specific context subclasses.  onRefresh();  // Check for listener beans and register them.  registerListeners();  // Instantiate singletons this late to allow them to access the message source.  beanFactory.preInstantiateSingletons();  // Last step: publish corresponding event.  publishEvent(new ContextRefreshedEvent(this));  }  catch (BeansException ex) {  // Destroy already created singletons to avoid dangling resources.  beanFactory.destroySingletons();  throw ex;  }
}

}