Spring Open Sourse Research(ContextLoaderListener Parts)

Spring 源码分析(ContextLoaderListener Parts)
ContextLoaderListener .java

java 代码

public class ContextLoaderListener implements ServletContextListener {

    private ContextLoader contextLoader;


    /**
     * Initialize the root web application context.
     */
    public void contextInitialized(ServletContextEvent event) {
        this.contextLoader = createContextLoader();
        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.
     * @return the current ContextLoader
     */
    public ContextLoader getContextLoader() {
        return this.contextLoader;
    }


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

}

2ContectLoader.java
//初始化工作,调用默认策略DEFAULT_STRATEGIES_PATH

java 代码

static {
    // Load default strategy implementations from properties file.
    // This is currently strictly internal and not meant to be customized
    // by application developers.
    try {
        ClassPathResource resource = new ClassPathResource(DEFAULT_STRATEGIES_PATH, ContextLoader.class);
        defaultStrategies = PropertiesLoaderUtils.loadProperties(resource);
    }
    catch (IOException ex) {
        throw new IllegalStateException("Could not load 'ContextLoader.properties': " + ex.getMessage());
    }
}

调用默认策略DEFAULT_STRATEGIES_PATH
Spring在web环境下会默认初始化XmlWebApplicationContext这个

defaultStrategies:

java 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.

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


this.contextLoader.initWebApplicationContext(event.getServletContext());

 初始化工作

java 代码

/**
    * Initialize Spring's web application context for the given servlet context,
    * according to the "contextClass" and "contextConfigLocation" context-params.
    * @param servletContext current servlet context
    * @return the new WebApplicationContext
    * @throws IllegalStateException if there is already a root application context present
    * @throws BeansException if the context failed to initialize
    * @see #CONTEXT_CLASS_PARAM
    * @see #CONFIG_LOCATION_PARAM
    */
   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!");
       }

       servletContext.log("Initializing Spring root WebApplicationContext");
       if (logger.isInfoEnabled()) {
           logger.info("Root WebApplicationContext: initialization started");
       }
       long startTime = System.currentTimeMillis();

       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.
           this.context = createWebApplicationContext(servletContext, parent);
           servletContext.setAttribute(
                   WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, this.context);

           if (logger.isDebugEnabled()) {
               logger.debug("Published root WebApplicationContext 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;
       }
   }

 initWebApplicationContext()调用了createWebApplicationContext()

java 代码

/**
    * Instantiate the root WebApplicationContext for this loader, either the
    * default context class or a custom context class if specified.
    * This implementation expects custom contexts to implement
    * ConfigurableWebApplicationContext. Can be overridden in subclasses.
    * @param servletContext current servlet context
    * @param parent the parent ApplicationContext to use, or null if none
    * @return the root WebApplicationContext
    * @throws BeansException if the context couldn't be initialized
    * @see ConfigurableWebApplicationContext
    */
   protected WebApplicationContext createWebApplicationContext(
           ServletContext servletContext, ApplicationContext parent) throws BeansException {
       //取得代用的从Context Class ,WebApplicationContext default
       Class contextClass = determineContextClass(servletContext);

       //判断contextClass是否是ConfigurableWebApplicationContext的子类，如果不是，throws ApplicationContextException
       if (!ConfigurableWebApplicationContext.class.isAssignableFrom(contextClass)) {
           throw new ApplicationContextException("Custom context class [" + contextClass.getName() +
                   "] is not of type [" + ConfigurableWebApplicationContext.class.getName() + "]");
       }
       //初始化这个类
       ConfigurableWebApplicationContext wac =
               (ConfigurableWebApplicationContext) BeanUtils.instantiateClass(contextClass);
       wac.setParent(parent);
       wac.setServletContext(servletContext);
       String configLocation = servletContext.getInitParameter(CONFIG_LOCATION_PARAM);
       if (configLocation != null) {
           wac.setConfigLocations(StringUtils.tokenizeToStringArray(configLocation,
                   ConfigurableWebApplicationContext.CONFIG_LOCATION_DELIMITERS));
       }

       wac.refresh();
       return wac;
   }

    

java 代码

/**
 * Return the WebApplicationContext implementation class to use, either the
 * default XmlWebApplicationContext or a custom context class if specified.
 * @param servletContext current servlet context
 * @return the WebApplicationContext implementation class to use
 * @throws ApplicationContextException if the context class couldn't be loaded
 * @see #CONTEXT_CLASS_PARAM
 * @see org.springframework.web.context.support.XmlWebApplicationContext
 */
protected Class determineContextClass(ServletContext servletContext) throws ApplicationContextException {
    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);
        }
    }
    else {
        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);
        }
    }
}

Notice: public static final String CONTEXT_CLASS_PARAM = "contextClass";

BeanUtils.java

    

java 代码

public static Object instantiateClass(Constructor ctor, Object[] args) throws BeanInstantiationException {
       Assert.notNull(ctor, "Constructor must not be null");
       try {
           if (!Modifier.isPublic(ctor.getModifiers()) ||
                   !Modifier.isPublic(ctor.getDeclaringClass().getModifiers())) {
               ctor.setAccessible(true);
           }
           return ctor.newInstance(args);
       }
       catch (InstantiationException ex) {
           throw new BeanInstantiationException(ctor.getDeclaringClass(),
                   "Is it an abstract class?", ex);
       }
       catch (IllegalAccessException ex) {
           throw new BeanInstantiationException(ctor.getDeclaringClass(),
                   "Has the class definition changed? Is the constructor accessible?", ex);
       }
       catch (IllegalArgumentException ex) {
           throw new BeanInstantiationException(ctor.getDeclaringClass(),
                   "Illegal arguments for constructor", ex);
       }
       catch (InvocationTargetException ex) {
           throw new BeanInstantiationException(ctor.getDeclaringClass(),
                   "Constructor threw exception", ex.getTargetException());
       }
   }

ConfigurableWebApplicationContext.java

java 代码

public interface ConfigurableWebApplicationContext extends WebApplicationContext, ConfigurableApplicationContext {
     //context para value分隔符
    String CONFIG_LOCATION_DELIMITERS = ",; \t\n";
    void setServletContext(ServletContext servletContext);
    void setServletConfig(ServletConfig servletConfig);
    ServletConfig getServletConfig();
    void setNamespace(String namespace);
    String getNamespace();
    void setConfigLocations(String[] configLocations);
    String[] getConfigLocations();
}

In a word, ContextLoaderListener invoke ContextLoader，and ContextLoader delegate and create ConfigurableWebApplicationContext
ConfigurableWebApplicationContext is an object including web servlet context,servletconfig,and contextConfigLocation.
Is is significant as follows

servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, this.context);
context is an object of ConfigurableWebApplicationContext;