@Override
public void contextInitialized(ServletContextEvent event) {
  initWebApplicationContext(event.getServletContext());
}

public WebApplicationContext initWebApplicationContext(ServletContext servletContext) {
  //Spring 啟動的句柄，spring容器開始啟動的根目錄
  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!");
  } else {
    Log logger = LogFactory.getLog(ContextLoader.class);
    servletContext.log("Initializing Spring root WebApplicationContext");
    if(logger.isInfoEnabled()) {
      logger.info("Root WebApplicationContext: initialization started");
    }
 
    long startTime = System.currentTimeMillis();
 
    try {
      //處理spring容器是否已經(jīng)創(chuàng)建（只創(chuàng)建沒有創(chuàng)建spring的各個bean）
      if(this.context == null) {
        this.context = this.createWebApplicationContext(servletContext);
      }
 
      if(this.context instanceof ConfigurableWebApplicationContext) {
        ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext)this.context;
        if(!cwac.isActive()) {
          if(cwac.getParent() == null) {
            ApplicationContext parent = this.loadParentContext(servletContext);
            cwac.setParent(parent);
          }
 
          //Spring容器創(chuàng)建完成后，加載spring容器的各個組件
          this.configureAndRefreshWebApplicationContext(cwac, servletContext);
        }
      }
 
      servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, this.context);
      ClassLoader ccl = Thread.currentThread().getContextClassLoader();
      if(ccl == ContextLoader.class.getClassLoader()) {
        currentContext = this.context;
      } else if(ccl != null) {
        currentContextPerThread.put(ccl, 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 var8) {
      logger.error("Context initialization failed", var8);
      servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, var8);
      throw var8;
    } catch (Error var9) {
      logger.error("Context initialization failed", var9);
      servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, var9);
      throw var9;
    }
  }
}

protected void configureAndRefreshWebApplicationContext(ConfigurableWebApplicationContext wac, ServletContext sc) {
		if (ObjectUtils.identityToString(wac).equals(wac.getId())) {
			// The application context id is still set to its original default value
			// -> assign a more useful id based on available information
			String idParam = sc.getInitParameter(CONTEXT_ID_PARAM);
			if (idParam != null) {
				wac.setId(idParam);
			}
			else {
				// Generate default id...
				wac.setId(ConfigurableWebApplicationContext.APPLICATION_CONTEXT_ID_PREFIX +
						ObjectUtils.getDisplayString(sc.getContextPath()));
			}
		}
 
		wac.setServletContext(sc);
		String configLocationParam = sc.getInitParameter(CONFIG_LOCATION_PARAM);
		if (configLocationParam != null) {
			wac.setConfigLocation(configLocationParam);
		}
 
		// The wac environment's #initPropertySources will be called in any case when the context
		// is refreshed; do it eagerly here to ensure servlet property sources are in place for
		// use in any post-processing or initialization that occurs below prior to #refresh
		ConfigurableEnvironment env = wac.getEnvironment();
		if (env instanceof ConfigurableWebEnvironment) {
			((ConfigurableWebEnvironment) env).initPropertySources(sc, null);
		}
 
		customizeContext(sc, wac);
		wac.refresh();
	}

public class Application{
 public static void main(String[] args) {
  ClassPathXmlApplicationContext ctx = new ClassPathXmlApplicationContext("/context.xml");
  ctx.start();
 }
}

@Override
	public Resource getResource(String location) {
		Assert.notNull(location, "Location must not be null");
		for (ProtocolResolver protocolResolver : this.protocolResolvers) {    // 1
			Resource resource = protocolResolver.resolve(location, this);
			if (resource != null) {return resource;}
		}
 
		if (location.startsWith("/")) {return getResourceByPath(location);}    //2
		else if (location.startsWith(CLASSPATH_URL_PREFIX)) {           //3
			return new ClassPathResource(location.substring(CLASSPATH_URL_PREFIX.length()), getClassLoader());
		}
		else {
			try {
				// Try to parse the location as a URL...
				URL url = new URL(location);               //4
				return new UrlResource(url);
			}
			catch (MalformedURLException ex) {
				// No URL -> resolve as resource path.
				return getResourceByPath(location);           //5
			}
		}
	}

class ClasspathPreProtocolResolver implements ProtocolResolver{
           private static String CLASS_PATH_PRE="classpath:";        
        public Resource resolve(String location, ResourceLoader resourceLoader) {
           if( location.startsWith(CLASS_PATH_PRE)) {
                return new ClassPathResource(location.substring(CLASS_PATH_PRE.length()));
           }       
           return null;
        }        
    }

protected Resource getResourceByPath(String path) {
		return new ClassPathContextResource(path, getClassLoader());
	}

<context-param>
    <param-name>contextConfigLocation</param-name>
    <param-value>classpath：/config/applicationContext.xml</param-value>
</context-param>