spring源码学习之applicationContext在web容器中加载过程

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

首先从WEB.XML入手

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

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

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);

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);

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

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

# 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

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()

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(StringlocationPattern);

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(StringlocationPattern);

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();

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

==>AbstractApplicationContext.refresh();

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;  
      }  
    }  
  }