SpringMVC视图解析

/**
 * Initialize the ViewResolvers used by this class.
 * <p>If no ViewResolver beans are defined in the BeanFactory for this
 * namespace, we default to InternalResourceViewResolver.
 */
private void initViewResolvers(ApplicationContext context) {
	this.viewResolvers = null;

	if (this.detectAllViewResolvers) {
		// Find all ViewResolvers in the ApplicationContext, including ancestor contexts.
		Map<String, ViewResolver> matchingBeans =
				BeanFactoryUtils.beansOfTypeIncludingAncestors(context, ViewResolver.class, true, false);
		if (!matchingBeans.isEmpty()) {
			this.viewResolvers = new ArrayList<>(matchingBeans.values());
			// We keep ViewResolvers in sorted order.
			AnnotationAwareOrderComparator.sort(this.viewResolvers);
		}
	}
	else {
		try {
			ViewResolver vr = context.getBean(VIEW_RESOLVER_BEAN_NAME, ViewResolver.class);
			this.viewResolvers = Collections.singletonList(vr);
		}
		catch (NoSuchBeanDefinitionException ex) {
			// Ignore, we'll add a default ViewResolver later.
		}
	}

	// Ensure we have at least one ViewResolver, by registering
	// a default ViewResolver if no other resolvers are found.
	// 如果没有自定义视图解析器，就会配置一个默认的InternalResourceViewResolver
	if (this.viewResolvers == null) {
		this.viewResolvers = getDefaultStrategies(context, ViewResolver.class);
		if (logger.isTraceEnabled()) {
			logger.trace("No ViewResolvers declared for servlet '" + getServletName() +
					"': using default strategies from DispatcherServlet.properties");
		}
	}
}

/**
 * Create a List of default strategy objects for the given strategy interface.
 * <p>The default implementation uses the "DispatcherServlet.properties" file (in the same
 * package as the DispatcherServlet class) to determine the class names. It instantiates
 * the strategy objects through the context's BeanFactory.
 * @param context the current WebApplicationContext
 * @param strategyInterface the strategy interface
 * @return the List of corresponding strategy objects
 */
@SuppressWarnings("unchecked")
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<>();
	}
}

   @Override
protected AbstractUrlBasedView buildView(String viewName) throws Exception {
	// 将调用父类的buildView方法，也就是AbstractUrlBasedView的buildView方法
	InternalResourceView view = (InternalResourceView) super.buildView(viewName);
	if (this.alwaysInclude != null) {
		view.setAlwaysInclude(this.alwaysInclude);
	}
	view.setPreventDispatchLoop(true);
	return view;
}

/**
 * Creates a new View instance of the specified view class and configures it.
 * Does <i>not</i> perform any lookup for pre-defined View instances.
 * <p>Spring lifecycle methods as defined by the bean container do not have to
 * be called here; those will be applied by the {@code loadView} method
 * after this method returns.
 * <p>Subclasses will typically call {@code super.buildView(viewName)}
 * first, before setting further properties themselves. {@code loadView}
 * will then apply Spring lifecycle methods at the end of this process.
 * @param viewName the name of the view to build
 * @return the View instance
 * @throws Exception if the view couldn't be resolved
 * @see #loadView(String, java.util.Locale)
 */
protected AbstractUrlBasedView buildView(String viewName) throws Exception {
	Class<?> viewClass = getViewClass(); // 这里将返回InternalResourceView.class
	Assert.state(viewClass != null, "No view class");

	AbstractUrlBasedView view = (AbstractUrlBasedView) BeanUtils.instantiateClass(viewClass);
	view.setUrl(getPrefix() + viewName + getSuffix());  //设置视图Url为前缀+视图名+后缀
       
	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;
}

// Did the handler return a view to render?
// mv为ModelAndView实例，完整的方法代码可以查看源码
		if (mv != null && !mv.wasCleared()) {
			render(mv, request, response);
			if (errorView) {
				WebUtils.clearErrorRequestAttributes(request);
			}
		}

/**
 * Render the given ModelAndView.
 * <p>This is the last stage in handling a request. It may involve resolving the view by name.
 * @param mv the ModelAndView to render
 * @param request current HTTP servlet request
 * @param response current HTTP servlet response
 * @throws ServletException if view is missing or cannot be resolved
 * @throws Exception if there's a problem rendering the view
 */
protected void render(ModelAndView mv, HttpServletRequest request, HttpServletResponse response) throws Exception {
	// Determine locale for request and apply it to the response.
	Locale locale =
			(this.localeResolver != null ? this.localeResolver.resolveLocale(request) : request.getLocale());
	response.setLocale(locale);  // 用地域解析器解析地域并设置好

	View view;
	String viewName = mv.getViewName();  // 获取视图名用于稍后的解析
	if (viewName != null) {
		// We need to resolve the view name.
		view = resolveViewName(viewName, mv.getModelInternal(), locale, request);
		if (view == null) {
			throw new ServletException("Could not resolve view with name '" + mv.getViewName() +
					"' in servlet with name '" + getServletName() + "'");
		}
	}
	else {
		// No need to lookup: the ModelAndView object contains the actual View object.
		view = mv.getView();
		if (view == null) {
			throw new ServletException("ModelAndView [" + mv + "] neither contains a view name nor a " +
					"View object in servlet with name '" + getServletName() + "'");
		}
	}

	// Delegate to the View object for rendering.
	if (logger.isTraceEnabled()) {
		logger.trace("Rendering view [" + view + "] ");
	}
	try {
		if (mv.getStatus() != null) {
			response.setStatus(mv.getStatus().value());
		}
		view.render(mv.getModelInternal(), request, response);
	}
	catch (Exception ex) {
		if (logger.isDebugEnabled()) {
			logger.debug("Error rendering view [" + view + "]", ex);
		}
		throw ex;
	}
}

@Nullable
protected View resolveViewName(String viewName, @Nullable Map<String, Object> model,
		Locale locale, HttpServletRequest request) throws Exception {
       // 将调用视图解析器解析视图
       // 将使用所有视图解析器进行解析，一但解析到有视图，就马上返回该视图
       // 因此这个过程受视图解析器的优先级影响较大
	if (this.viewResolvers != null) {
		for (ViewResolver viewResolver : this.viewResolvers) {
			View view = viewResolver.resolveViewName(viewName, locale);
			if (view != null) {
				return view;
			}
		}
	}
	return null;
}

@Override
public void render(@Nullable Map<String, ?> model, HttpServletRequest request,
		HttpServletResponse response) throws Exception {

	if (logger.isDebugEnabled()) {
		logger.debug("View " + formatViewName() +
				", model " + (model != null ? model : Collections.emptyMap()) +
				(this.staticAttributes.isEmpty() ? "" : ", static attributes " + this.staticAttributes));
	}

	Map<String, Object> mergedModel = createMergedOutputModel(model, request, response);
	prepareResponse(request, response);

	// 该方法为抽象方法，需要子类自行实现
	renderMergedOutputModel(mergedModel, getRequestToExpose(request), response);
}

/**
 * Render the internal resource given the specified model.
 * This includes setting the model as request attributes.
 */
@Override
protected void renderMergedOutputModel(
		Map<String, Object> model, HttpServletRequest request, HttpServletResponse response) throws Exception {

	// Expose the model object as request attributes.
	exposeModelAsRequestAttributes(model, request);

	// Expose helpers as request attributes, if any.
	exposeHelpers(request);

	// Determine the path for the request dispatcher.
	String dispatcherPath = prepareForRendering(request, response);

	// Obtain a RequestDispatcher for the target resource (typically a JSP).
	// 这里将使用Servlet容器实现的RequestDispatcher去获取目标资源
	RequestDispatcher rd = getRequestDispatcher(request, dispatcherPath);
	if (rd == null) {
		throw new ServletException("Could not get RequestDispatcher for [" + getUrl() +
				"]: Check that the corresponding file exists within your web application archive!");
	}

	// If already included or response already committed, perform include, else forward.
	if (useInclude(request, response)) {
		response.setContentType(getContentType());
		if (logger.isDebugEnabled()) {
			logger.debug("Including [" + getUrl() + "]");
		}
		rd.include(request, response);
	}

	else {
		// Note: The forwarded resource is supposed to determine the content type itself.
		if (logger.isDebugEnabled()) {
			logger.debug("Forwarding to [" + getUrl() + "]");
		}
		rd.forward(request, response);
	}
}

@Controller
@RequestMapping("/html")
public class HtmlController {

    @GetMapping
    public String simpleHtml(){
        return "/WEB-INF/views/simple.jsp";
    }
}