从DispatcherServlet到ViewResolver

tomcat启动DispatcherServlet默认加载的ViewResolver只有org.springframework.web.servlet.view.InternalResourceViewResolver和自定义HandlerExceptionResolver。

ViewResolver里面只有一个方法resolveViewName(String viewName, Locale locale)，按名称解析给定的视图。

DispatcherServlet在doDispatch(HttpServletRequest request, HttpServletResponse response)方法中调用processDispatchResult(HttpServletRequest request, HttpServletResponse response, @Nullable HandlerExecutionChain mappedHandler, @Nullable ModelAndView mv, @Nullable Exception exception)方法处理程序调用结果，

当ModelAndView存在且没有被清除时，调用read(ModelAndView mv, HttpServletRequest request, HttpServletResponse response)方法，

如果ModelAndView的视图名称不为空时，调用resolveViewName(String viewName, @Nullable Map<String, Object> model, Locale locale, HttpServletRequest request)方法解析视图名称。

resolveViewName方法先去判断是否有缓存如果有缓存，那就取缓存里面的View，如果没有，则创建一个新的View。

创建View流程如下：

protected View createView(String viewName, Locale locale) throws Exception {
		return loadView(viewName, locale);
	}

protected View loadView(String viewName, Locale locale) throws Exception {
		AbstractUrlBasedView view = buildView(viewName);
		View result = applyLifecycleMethods(viewName, view);
		return (view.checkResource(locale) ? result : null);
	}

protected AbstractUrlBasedView buildView(String viewName) throws Exception {
		Class<?> viewClass = getViewClass();
		Assert.state(viewClass != null, "No view class");

		AbstractUrlBasedView view = (AbstractUrlBasedView) BeanUtils.instantiateClass(viewClass);
		view.setUrl(getPrefix() + viewName + getSuffix());

		String contentType = getContentType();
		if (contentType != null) {
			view.setContentType(contentType);
		}

		view.setRequestContextAttribute(getRequestContextAttribute());
		view.setAttributesMap(getAttributesMap());

		Boolean exposePathVariables = getExposePathVariables();
		if (exposePathVariables != null) {
			view.setExposePathVariables(exposePathVariables);
		}
		Boolean exposeContextBeansAsAttributes = getExposeContextBeansAsAttributes();
		if (exposeContextBeansAsAttributes != null) {
			view.setExposeContextBeansAsAttributes(exposeContextBeansAsAttributes);
		}
		String[] exposedContextBeanNames = getExposedContextBeanNames();
		if (exposedContextBeanNames != null) {
			view.setExposedContextBeanNames(exposedContextBeanNames);
		}

		return view;
	}