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

 
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==>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.XmlWebApplicationContext
org.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};
    }
  }
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| web.xml 中的listener、 filter、servlet ...
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