初始化处理器适配器

private void initHandlerAdapters(ApplicationContext context) {
    this.handlerAdapters = null;

    if (this.detectAllHandlerAdapters) {
        //从上下文（包括父上下文）中查找所有HandlerAdapter实现类
        Map<String, HandlerAdapter> matchingBeans =BeanFactoryUtils.beansOfTypeIncludingAncestors(context, HandlerAdapter.class, true, false);
        if (!matchingBeans.isEmpty()) {
            this.handlerAdapters = new ArrayList<>(matchingBeans.values());
            AnnotationAwareOrderComparator.sort(this.handlerAdapters);
        }
    }
    else {
        try {
            //这里取bean名字为handlerAdapter，类型为HandlerAdapter的处理器适配器
            HandlerAdapter ha = context.getBean(HANDLER_ADAPTER_BEAN_NAME, HandlerAdapter.class);
            this.handlerAdapters = Collections.singletonList(ha);
        }
        catch (NoSuchBeanDefinitionException ex) {
            
        }
    }
    
    /**
    如果没找到，则从默认规则里取出指定的三个实现类：HttpRequestHandlerAdapter、SimpleControllerHandlerAdapter、RequestMappingHandlerAdapter
    **/
    if (this.handlerAdapters == null) {
        this.handlerAdapters = getDefaultStrategies(context, HandlerAdapter.class);     
    }
}

初始化试图解析器

private void initViewResolvers(ApplicationContext context) {
    this.viewResolvers = null;

    if (this.detectAllViewResolvers) {
        //从上下文（包括父上下文）中查找所有ViewResolver实现类
        Map<String, ViewResolver> matchingBeans =BeanFactoryUtils.beansOfTypeIncludingAncestors(context, ViewResolver.class, true, false);
        if (!matchingBeans.isEmpty()) {
            this.viewResolvers = new ArrayList<>(matchingBeans.values());
            AnnotationAwareOrderComparator.sort(this.viewResolvers);
        }
    }
    else {
        try {
            ViewResolver vr = context.getBean(VIEW_RESOLVER_BEAN_NAME, ViewResolver.class);
            this.viewResolvers = Collections.singletonList(vr);
        }
        catch (NoSuchBeanDefinitionException ex) {
            
        }
    }
    
    /**
    如果没找到，则从默认规则里取出指定的实现类：InternalResourceViewResolver
    **/
    if (this.viewResolvers == null) {
        this.viewResolvers = getDefaultStrategies(context, ViewResolver.class); 
    }
}

         三大组件的初始化最后判断为NULL时都会调用getDefaultStrategies方法，也就是从DispatcherServlet.properties中取出指定默认值。

protected <T> List<T> getDefaultStrategies(ApplicationContext context, Class<T> strategyInterface) {
    String key = strategyInterface.getName();
    String value = defaultStrategies.getProperty(key);
    if (value != null) {
        String[] classNames = StringUtils.commaDelimitedListToStringArray(value);
        List<T> strategies = new ArrayList<>(classNames.length);
        for (String className : classNames) {
            try {
                Class<?> clazz = ClassUtils.forName(className, DispatcherServlet.class.getClassLoader());
                Object strategy = createDefaultStrategy(context, clazz);
                strategies.add((T) strategy);
            }
            catch (ClassNotFoundException ex) {
                throw new BeanInitializationException("Could not find DispatcherServlet's default strategy class [" + className +"] for interface [" + key + "]", ex);
            }
            catch (LinkageError err) {
                throw new BeanInitializationException("Unresolvable class definition for DispatcherServlet's default strategy class [" +className + "] for interface [" + key + "]", err);
            }
        }
        return strategies;
    }
    else {
        return new LinkedList<>();
    }
}

DispatcherServlet请求处理过程