調(diào)用過程
org.springframework.web.servler.ViewResolver 用來決定應(yīng)該用哪個(gè)org.springframework.web.servlet.View的實(shí)例來創(chuàng)建并發(fā)送給客戶端的response。
Dispatcherservlet 收到一個(gè)由request handler （通常為Controller中處理用戶請求的方法）處理完用戶請求而返回的值之后，在DispatcherServlet#doDispatch中調(diào)用了processDispatchResult：
/**
* Handle the result of handler selection and handler invocation, which is
* either a ModelAndView or an Exception to be resolved to a ModelAndView.
*/
private void processDispatchResult(HttpServletRequest request, HttpServletResponse response,
HandlerExecutionChain mappedHandler, ModelAndView mv, Exception exception) throws Exception
之后的call hierarchy如下：
在DispatcherServlet#resolveViewName中锌历，遍歷當(dāng)前的所有ViewResolver，調(diào)用其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);
if (view != null) {
return view;
}
}
return null;
}
因此试幽，ViewResolver#resolveViewName的語義就是：對(duì)于給定的viewName（由Controller返回），若是能夠處理卦碾，則返回對(duì)應(yīng)的View的實(shí)例铺坞，否則返回null，由下一個(gè)ViewResolver 處理蔗坯。
找到合適的view之后康震，即調(diào)用其render方法燎含，將從request handler 返回的數(shù)據(jù)（在spring mvc中稱為model）宾濒，進(jìn)行數(shù)據(jù)綁定并對(duì)客戶端進(jìn)行相應(yīng)：
//DispatcherServlet#render(...):
view.render(mv.getModelInternal(), request, response);
詳情可參考：SpringMVC#mvc-viewresolver
注冊ViewResolver
從上面的代碼可以看到，所有的ViewResolver保存在DispatcherServlet#viewResolvers中屏箍，而viewResolvers這個(gè)列表的值從context里面绘梦、與獲取其他bean一樣、來獲雀翱：
private void initViewResolvers(ApplicationContext context) {
this.viewResolvers = null;
if (this.detectAllViewResolvers) {
// Find all ViewResolvers in the ApplicationContext, including ancestor contexts.
Map<String, ViewResolver> matchingBeans =
//從context中獲取類型為ViewResolver的bean
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 {
//從context中獲取類型為ViewResolver的bean
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.
if (this.viewResolvers == null) {
this.viewResolvers = getDefaultStrategies(context, ViewResolver.class);
if (logger.isDebugEnabled()) {
logger.debug("No ViewResolvers found in servlet '" + getServletName() + "': using default");
}
}
}
這里可以看到卸奉，ViewResolver是有順序的（可以通過@order 來控制bean的順序），若是多個(gè)ViewResolver可以處理同樣的viewName颖御，那么排在后面的ViewResolver將不起作用榄棵。
View#render
View#render 方法負(fù)責(zé)輸出最終的HTTP response.
其接收三個(gè)參數(shù)：
- Map<String, ?> model: 從Controller那邊獲得的跟業(yè)務(wù)相關(guān)的數(shù)據(jù)
- HttpServletRequest request: ?當(dāng)前的HTTP request
- HttpServletResponse response：當(dāng)前正在構(gòu)建的HTTP response，可將內(nèi)容寫入并發(fā)送給客戶端
SpringMVC 提供了許多默認(rèn)的View的實(shí)現(xiàn)類，可以滿足大部分開發(fā)的需求——?如果完全使用spring框架的話疹鳄。如果你打算自己控制render過程拧略，有自己的一套模板機(jī)制，那么就可以創(chuàng)建自定義View的實(shí)現(xiàn)類了瘪弓。
總結(jié)
這里簡單講述了當(dāng)一個(gè)request被處理完成之后垫蛆，將處理結(jié)果轉(zhuǎn)化為response的過程中涉及到的類。大致流程如下：
- 接收到客戶端的request腺怯，根據(jù)request查找對(duì)應(yīng)的request handler（一般為Controller中的方法）
- request handler處理完之后返回袱饭，spring將處理結(jié)果包裝為
ModelAndView（將在其他文章中介紹這個(gè)過程） -
DispatcherServlet根據(jù)ModelAndView的view name來選擇對(duì)應(yīng)的View：遍歷ViewResolver，ViewResolver根據(jù)view name來返回對(duì)應(yīng)的View的實(shí)現(xiàn)類（或返回null并交給下一個(gè)ViewResolver） - 調(diào)用
View#render來生成最終的response呛占，在View的實(shí)現(xiàn)類中實(shí)現(xiàn)最終渲染并輸出到response的過程虑乖。
