初探spring applicationContext在web容器中加载过程 首先从WEB.XML入手

 ==>web.xml(1)

 

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<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>    <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

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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

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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);

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 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);

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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

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  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

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# 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.XmlWebApplicationContextorg.springframework.web.context.WebApplicationContext=org.springframework.web.context.support.XmlWebApplicationContext 

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

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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};    }  }