ContextLoaderListener 加载过程

需要注意的是：

ContextLoader.properties

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

ContextLoader.java

private static final String DEFAULT_STRATEGIES_PATH = "ContextLoader.properties";
static {
        // Load default strategy implementations from properties file.
        // This is currently strictly internal and not meant to be customized
        // by application developers.
        try {
            //加载Resource路径  
            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());
        }
    }
protected Class<?> determineContextClass(ServletContext servletContext) {
        String contextClassName = servletContext.getInitParameter(CONTEXT_CLASS_PARAM);
        if (contextClassName != null) {
            try {
                return ClassUtils.forName(contextClassName, ClassUtils.getDefaultClassLoader());
            }
            catch (ClassNotFoundException ex) {
                throw new ApplicationContextException(
                        "Failed to load custom context class [" + contextClassName + "]", ex);
            }
        }
        else {
            //通过key为WebApplicationContext获取到value 为： org.springframework.web.context.support.XmlWebApplicationContext
            contextClassName = defaultStrategies.getProperty(WebApplicationContext.class.getName());
            try {
                //通过反射拿到XmlWebApplicationContext
                return ClassUtils.forName(contextClassName, ContextLoader.class.getClassLoader());
            }
            catch (ClassNotFoundException ex) {
                throw new ApplicationContextException(
                        "Failed to load default context class [" + contextClassName + "]", ex);
            }
        }
    }