spring-mvc 视图模式之freemarker整合解析

spring-mvc 版本4.04

今天翻项目中freemarker相关代码，疑惑springmvc是怎么发现freemarker的，因而单步进去。
DispatcherServlet的doDispatch方法里有这么一句：

processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);

能够猜到，这是handler业务处理后，到渲染页面的阶段了，也就是freemarker该出场的时候了。

进入processDispatchResult这个方法，看到这么一段

// Did the handler return a view to render? 返回一个view 去渲染
if (mv != null && !mv.wasCleared()) {
	render(mv, request, response);//就是渲染了
	if (errorView) {
		WebUtils.clearErrorRequestAttributes(request);
	}
}

而后render方法，看到

View view;
if (mv.isReference()) {//mv 是String类型的，好比url
	// We need to resolve the view name.
	view = resolveViewName(mv.getViewName(), mv.getModelInternal(), locale, request);//获取来渲染页面的view
	if (view == null) {
		throw new ServletException("Could not resolve view with name '" + mv.getViewName() +
				"' in servlet with name '" + getServletName() + "'");
	}
}

看到resolveViewName方法

protected View resolveViewName(String viewName, Map<String, Object> model, Locale locale,
		HttpServletRequest request) throws Exception {

	for (ViewResolver viewResolver : this.viewResolvers) {
		View view = viewResolver.resolveViewName(viewName, locale);
		//建立根据viewName（其实就是controller里返回的url，好比/wiew/test.ftl）建立view
		//那随便一个url都能有相应的view吗？固然不是。好比要先匹配，这个下面说，
		if (view != null) {
			return view;
		}
	}
	return null;
}

原来view解决方案已经都存在viewResolvers对象里了，那何时存的呢，代码里搜索下，找到以下方法：

/**
 * 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) {//boolean值，是否自动检测全部的ViewResolver，
		// Find all ViewResolvers in the ApplicationContext, including ancestor contexts.
		//是自动检测，就用BeanFactoryUtils的beansOfTypeIncludingAncestors方法，找全部的ViewResolver
		//能够看到这个方法颇有用，在项目也能够用，，可你找到全部ViewResolver.class类型或子类的bean，很好用。
//这也体现了mvc框架的v的部分。任何实现了ViewResolver接口的类，均可做为视图用
		Map<String, ViewResolver> matchingBeans =
				BeanFactoryUtils.beansOfTypeIncludingAncestors(context, ViewResolver.class, true, false);
		if (!matchingBeans.isEmpty()) {
			this.viewResolvers = new ArrayList<ViewResolver>(matchingBeans.values());
			// We keep ViewResolvers in sorted order.
			OrderComparator.sort(this.viewResolvers);
		}
	}
	else {
		try {
			ViewResolver vr = context.getBean(VIEW_RESOLVER_BEAN_NAME, ViewResolver.class);//若是不自动检测
			//String VIEW_RESOLVER_BEAN_NAME = "viewResolver";  就找名字为viewResolver的bean做为ViewResolver
			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.
        //以上都没找到视图，只有获取一个默认的。
	if (this.viewResolvers == null) {
		this.viewResolvers = getDefaultStrategies(context, ViewResolver.class);
		if (logger.isDebugEnabled()) {
			logger.debug("No ViewResolvers found in servlet '" + getServletName() + "': using default");
		}
	}
}

initViewResolvers这个方法，是在onRefresh的调用的，实际上是重写了父类的方法，
在spring的初始化时自动被调用。spring模板方法的神力开始起做用了。

protected void onRefresh(ApplicationContext context) {
	initStrategies(context);
}

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以上是spring-mvc怎么发现第三方viewResolver（不限freemarker）的，而后看看，请求来的url怎么找到匹配的view的，接着说上面遗留的问题
再看这句代码：

View view = viewResolver.resolveViewName(viewName, locale);

这个方法是org.springframework.web.servlet.view.freemarker.FreeMarkerViewResolver父类AbstractCachingViewResolver实现的。
跟进去：

@Override
public View resolveViewName(String viewName, Locale locale) throws Exception {
	if (!isCache()) {//缓存无处不在
		return createView(viewName, locale);//跟进去
	}
	else {
		Object cacheKey = getCacheKey(viewName, locale);
		View view = this.viewAccessCache.get(cacheKey);
		if (view == null) {
			synchronized (this.viewCreationCache) {
				view = this.viewCreationCache.get(cacheKey);
				if (view == null) {
					// Ask the subclass to create the View object.
					view = createView(viewName, locale);
					if (view == null && this.cacheUnresolved) {
						view = UNRESOLVED_VIEW;
					}
					if (view != null) {
						this.viewAccessCache.put(cacheKey, view);
						this.viewCreationCache.put(cacheKey, view);
						if (logger.isTraceEnabled()) {
							logger.trace("Cached view [" + cacheKey + "]");
						}
					}
				}
			}
		}
		return (view != UNRESOLVED_VIEW ? view : null);
	}
}

//因为UrlBasedViewResolver类从新写了这个方法因此，是UrlBasedViewResolver的createView方法
@Override
protected View createView(String viewName, Locale locale) throws Exception {
	// If this resolver is not supposed to handle the given view,
	// return null to pass on to the next resolver in the chain.
	//就在这里，代码首先检查resolver是否支持这个viewName（url）
	if (!canHandle(viewName, locale)) {
		return null;
	}
	// Check for special "redirect:" prefix.
	if (viewName.startsWith(REDIRECT_URL_PREFIX)) {
		String redirectUrl = viewName.substring(REDIRECT_URL_PREFIX.length());
		RedirectView view = new RedirectView(redirectUrl, isRedirectContextRelative(), isRedirectHttp10Compatible());
		return applyLifecycleMethods(viewName, view);
	}
	// Check for special "forward:" prefix.
	if (viewName.startsWith(FORWARD_URL_PREFIX)) {
		String forwardUrl = viewName.substring(FORWARD_URL_PREFIX.length());
		return new InternalResourceView(forwardUrl);
	}
	// Else fall back to superclass implementation: calling loadView.
	return super.createView(viewName, locale);
}
//在这里
protected boolean canHandle(String viewName, Locale locale) {
	String[] viewNames = getViewNames();
	//viewNames就是在xml文件里配置的如，freemarker
	//<property name="viewNames">
	//<array>
	//<value>*.ftl</value>
		//<value>*.html</value>
	//</array>
	//</property>
	return (viewNames == null || PatternMatchUtils.simpleMatch(viewNames, viewName));//作模式匹配
}

最后类图，注意方法的重写。子类老是调用最近上级节点方法。