前言
上一篇文章写得是SpringMVC组件初始化，这篇文章我们来探讨一下SpringMVC的执行流程
SpringMVC执行流程
SpringMVC执行流程几乎是在面试时面试官对SpringMVC部分的必问之题，下面是SpirngMVC的执行原理图
这个是请求在SpringMVC的执行流程
- DispatcherServlet：请求打过来由DispatcherServlet处理，它是 SpringMVC 中的前端控制器(中央控制器), 负责接收 Request 并将 Request 转发给对应的处理组件
- HandlerMapping：HandlerMapping 维护了 url 和 Controller(Handler)的 映 射关系 。 DispatcherServlet 接 收 请求, 然 后 从 HandlerMapping 查找处理请求的Controller(Handler)，标注了@RequestMapping 的每个 method 都可以看成是一个 Handler，HandlerMapping 在请求到达之后， 它的作用便是找到请求相应的处理器 Handler 和 Interceptors。
- HandlerAdapter：SpringMVC通过HandlerAdapter对Handler进行执行，这是适配器模式的应用，通过扩展适配器可以对更多类型的处理器进行执行。它的作用就是按照特定的规则去执行 Controller (Handler)
- Handler : Controller (Handler)负责处理请求，Controller 执行后并返回 ModelAndView 对象，其中包括了数据模型和逻辑视图,,ModelAndView 是封装结果 视图的组件。Handler把结果返回给HandlerAdapter，HandlerAdapter把结果返回给DispatcherServlet前端控制器。
- ViewResolver：DispatcherServlet收到ModelAndView,调用视图解析器(ViewResolver)来解析HandlerAdapter传递的ModelAndView。Handler执行完成后返回的是逻辑视图，也就是视图名字，一个String ，还有一个Model就是数据模型，封装成ModelAndView。ViewResolver视图解析的作用就是根据视图名，把本地模板文件(比如：xx.jsp;xx.ftl)解析为View视图对象。View用来渲染视图，也就是负责把Handler返回的数据模型model,填充到模板(jsp;ftl)形成html格式的静态内容。
- 最后就是把生成的html通过response写给浏览器，浏览器进行html渲染展示。
核心类认识
开始之前先来认识几个对象，否则下面会晕菜
HandlerMethod ：是的controller中方法的封装，其中包括在Controller的Bean对象以及Method方法对象
public class HandlerMethod {
/** Logger that is available to subclasses */
protected final Log logger = LogFactory.getLog(HandlerMethod.class);
private final Object bean; //controller对应的bean
private final Method method; //方法对象
private final BeanFactory beanFactory;
private final MethodParameter[] parameters;
private final Method bridgedMethod;
MappedInterceptor ：对拦截器的封装
public final class MappedInterceptor {
private final String[] includePatterns;
private final String[] excludePatterns; //排除
private final HandlerInterceptor interceptor; //拦截器
RequestMappingInfo : 对@Controller和@RequestMapping注解的类的方法进行解析，然后把解析的结果封装成RequestMappingInfo ， 对象中包含了针对@RequestMapping注解的6个属性的匹配条件，DispaterServlet需要根据找到请求匹配的Handler就需要满足6个匹配条件。
- PatternsRequestCondition ：模式请求路径过滤器 ，根据request请求路径进行匹配
- RequestMethodsRequestCondition ： 请求方法过滤器，根据request请求方式进行匹配
- ParamsRequestCondition ：请求参数过滤器，根据请求的参数进行匹配
- HeadersRequestCondition ： 请求过滤器 ，根据请求头进行匹配
- ConsumesRequestCondition ：根据 筛选出同请求Accpet匹配的媒体类型表达式列表
- ProducesRequestCondition ：应答媒体类型过滤器，根据请求Content-Type媒体类型进行匹配
- RequestCondition (optional, custom request condition)
public final class RequestMappingInfo implements RequestCondition<RequestMappingInfo> {
//根据url进行匹配
private final PatternsRequestCondition patternsCondition;
//方法匹配条件
private final RequestMethodsRequestCondition methodsCondition;
//请求参数过滤器，参数匹配条件
private final ParamsRequestCondition paramsCondition;
//头字段过滤器，请求头匹配条件
private final HeadersRequestCondition headersCondition;
//Consumes匹配条件
private final ConsumesRequestCondition consumesCondition;
// Produces匹配条件
private final ProducesRequestCondition producesCondition;
DispatchServlet执行流程
DispatchServlet是一个Servlet，请求进来会执行 DispatcherServlet#doService 方法
protected void doService(HttpServletRequest request, HttpServletResponse response) throws Exception {
...省略...
// Make framework objects available to handlers and view objects.
//把容器对象设置到request
request.setAttribute(WEB_APPLICATION_CONTEXT_ATTRIBUTE, getWebApplicationContext());
//把localeResolver设置给request
request.setAttribute(LOCALE_RESOLVER_ATTRIBUTE, this.localeResolver);
//把themeResolver设置给request
request.setAttribute(THEME_RESOLVER_ATTRIBUTE, this.themeResolver);
request.setAttribute(THEME_SOURCE_ATTRIBUTE, getThemeSource());
FlashMap inputFlashMap = this.flashMapManager.retrieveAndUpdate(request, response);
if (inputFlashMap != null) {
request.setAttribute(INPUT_FLASH_MAP_ATTRIBUTE, Collections.unmodifiableMap(inputFlashMap));
}
//设置flashMapManager
request.setAttribute(OUTPUT_FLASH_MAP_ATTRIBUTE, new FlashMap());
request.setAttribute(FLASH_MAP_MANAGER_ATTRIBUTE, this.flashMapManager);
try {
//执行请求分发
doDispatch(request, response);
}
finally {
if (WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {
return;
}
// Restore the original attribute snapshot, in case of an include.
if (attributesSnapshot != null) {
restoreAttributesAfterInclude(request, attributesSnapshot);
}
}
}
DispatcherServlet#doService调用了DispatcherServlet#doDispatch 做请求处理
protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
HttpServletRequest processedRequest = request;
HandlerExecutionChain mappedHandler = null;
boolean multipartRequestParsed = false;
//管理异步请求
WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
try {
ModelAndView mv = null;
Exception dispatchException = null;
try {
//1.检查是否是Multipart文件上传
processedRequest = checkMultipart(request);
multipartRequestParsed = processedRequest != request;
// Determine handler for the current request.
//2.遍历所有 handlerMappings 找到当前请求对应的handler，
//比如：RequestMappingHandlerMapping 中维护了一个LinkedHashMap类型的handlerMethods，
//是对HandlerMethod的存储。底层根据URL从handlerMethods匹配一个HandlerMethod，
//然后把HandlerMethod封装到一个HandlerExecutionChain中
//HandlerMethod是对controller方法method的封装，
//这里拿到的是HandlerExecutionChain handler执行链，其中封装了Handler和inteceptor
mappedHandler = getHandler(processedRequest, false);
if (mappedHandler == null || mappedHandler.getHandler() == null) {
//如果没找到会走404
noHandlerFound(processedRequest, response);
return;
}
// Determine handler adapter for the current request.
//3.从handlerAdapters中循环，找到支持handler的，处理请求适配器HandlerAdapter(如：RequestMappingHandlerAdapter)
HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());
// Process last-modified header, if supported by the handler.
//处理lastModified
String method = request.getMethod();
boolean isGet = "GET".equals(method);
if (isGet || "HEAD".equals(method)) {
long lastModified = ha.getLastModified(request, mappedHandler.getHandler());
if (logger.isDebugEnabled()) {
String requestUri = urlPathHelper.getRequestUri(request);
logger.debug("Last-Modified value for [" + requestUri + "] is: " + lastModified);
}
if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
return;
}
}
//4.调用拦截器的preHandle
if (!mappedHandler.applyPreHandle(processedRequest, response)) {
return;
}
try {
// Actually invoke the handler.
//5.调用 HandlerAdapter 实际执行handler,返回ModelAndView
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
}
finally {
if (asyncManager.isConcurrentHandlingStarted()) {
return;
}
}
//6.处理默认的视图名，如果mv != null && !mv.hasView()
//就会使用RequestToViewNameTranslator#getViewName解析一个默认的view
applyDefaultViewName(request, mv);
//7.调用拦截器的postHandle
mappedHandler.applyPostHandle(processedRequest, response, mv);
}
catch (Exception ex) {
dispatchException = ex;
}
//8.处理结果，内部会使用viewResolver.resolveViewName渲染视图得到View对象
//然后执行：View#render方法渲染
processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
}
catch (Exception ex) {
triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
}
catch (Error err) {
triggerAfterCompletionWithError(processedRequest, response, mappedHandler, err);
}
finally {
if (asyncManager.isConcurrentHandlingStarted()) {
// Instead of postHandle and afterCompletion
mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
return;
}
// Clean up any resources used by a multipart request.
if (multipartRequestParsed) {
cleanupMultipart(processedRequest);
}
}
}
这里对核心方法做一个解释
查找HandlerMethod
getHandler 方法：该方法是遍历所有 handlerMappings ，找到合适的HandlerMapping，然后通过HandlerMapping#getHandler查找当前请求对应的HandlerMethod。(HandlerMethod是对controller中方法的封装),这里拿到的是HandlerExecutionChain 执行链而不是HandlerMethod，HandlerExecutionChain中封装了HandlerMethod和inteceptor拦截器；见：org.springframework.web.servlet.DispatcherServlet#getHandler(javax.servlet.http.HttpServletRequest)
protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
for (HandlerMapping hm : this.handlerMappings) {
if (logger.isTraceEnabled()) {
logger.trace(
"Testing handler map [" + hm + "] in DispatcherServlet with name '" + getServletName() + "'");
}
//使用HandlerMapping 获取处理请求的Handler,封装到HandlerExecutionChain执行链对象中
//HandlerExecutionChain包括了HandlerMethod和interceptor拦截器
HandlerExecutionChain handler = hm.getHandler(request);
if (handler != null) {
return handler;
}
}
return null;
}
public final HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
//找到Handler
Object handler = getHandlerInternal(request);
if (handler == null) {
handler = getDefaultHandler();
}
if (handler == null) {
return null;
}
// Bean name or resolved handler?
if (handler instanceof String) {
String handlerName = (String) handler;
handler = getApplicationContext().getBean(handlerName);
}
//把handler封装成HandlerExecutionChain ，其中还包括了拦截器的封装
return getHandlerExecutionChain(handler, request);
}
protected HandlerExecutionChain getHandlerExecutionChain(Object handler, HttpServletRequest request) {
//创建一个Handler执行链对象
HandlerExecutionChain chain =
(handler instanceof HandlerExecutionChain) ?
(HandlerExecutionChain) handler : new HandlerExecutionChain(handler);
//添加拦截器到HandlerExecutionChain
chain.addInterceptors(getAdaptedInterceptors());
String lookupPath = urlPathHelper.getLookupPathForRequest(request);
for (MappedInterceptor mappedInterceptor : mappedInterceptors) {
if (mappedInterceptor.matches(lookupPath, pathMatcher)) {
chain.addInterceptor(mappedInterceptor.getInterceptor());
}
}
return chain;
}
getHandler方法最终会走到org.springframework.web.servlet.handler.AbstractHandlerMethodMapping#getHandlerInternal ，该方法就是根据request查找一个HandlerMethod
protected HandlerMethod getHandlerInternal(HttpServletRequest request) throws Exception {
//拿到请求的路径
String lookupPath = getUrlPathHelper().getLookupPathForRequest(request);
if (logger.isDebugEnabled()) {
logger.debug("Looking up handler method for path " + lookupPath);
}
//根据请求路径，找到匹配的HandlerMethod
HandlerMethod handlerMethod = lookupHandlerMethod(lookupPath, request);
if (logger.isDebugEnabled()) {
if (handlerMethod != null) {
logger.debug("Returning handler method [" + handlerMethod + "]");
}
else {
logger.debug("Did not find handler method for [" + lookupPath + "]");
}
}
return (handlerMethod != null) ? handlerMethod.createWithResolvedBean() : null;
}
这里在拿到请求的路径，根据请求路径，找到匹配的HandlerMethod，再往里面走
protected HandlerMethod lookupHandlerMethod(String lookupPath, HttpServletRequest request) throws Exception {
//matches是requestMppingInfo和HandlerMethod的匹配器集合
List<Match> matches = new ArrayList<Match>();
//根据请求的路径，从 this.urlMap中拿到RequestMappingInfo,
//urlMap 是一个LinkedHashMap，存储了Url路径和RequestMappingInfo的映射关系
List<T> directPathMatches = this.urlMap.get(lookupPath);
if (directPathMatches != null) {
addMatchingMappings(directPathMatches, matches, request);
}
if (matches.isEmpty()) {
// No choice but to go through all mappings
//如果从urlMap中没有找到RequestMappingInfo，那么matches就是空的
//根据Request对象封装一个requestMppingInfo，然后handlerMethods的keySet中拿到对应的HandlerMethod，(会根据Request中的URL,请求方式，参数params，请求头headers，consumes，produces去匹配handlerMethods.keySet中的requestMppingInfo)
//然后从handlerMethods根据requestMppingInfo拿到HandlerMethod
//把requestMppingInfo和HandlerMethod封装成Match添加到matches中
addMatchingMappings(this.handlerMethods.keySet(), matches, request);
}
if (!matches.isEmpty()) {
Comparator<Match> comparator = new MatchComparator(getMappingComparator(request));
Collections.sort(matches, comparator);
if (logger.isTraceEnabled()) {
logger.trace("Found " + matches.size() + " matching mapping(s) for [" + lookupPath + "] : " + matches);
}
Match bestMatch = matches.get(0);
if (matches.size() > 1) {
Match secondBestMatch = matches.get(1);
if (comparator.compare(bestMatch, secondBestMatch) == 0) {
Method m1 = bestMatch.handlerMethod.getMethod();
Method m2 = secondBestMatch.handlerMethod.getMethod();
throw new IllegalStateException(
"Ambiguous handler methods mapped for HTTP path '" + request.getRequestURL() + "': {" +
m1 + ", " + m2 + "}");
}
}
handleMatch(bestMatch.mapping, lookupPath, request);
//从bestMatch拿到Handler
return bestMatch.handlerMethod;
}
else {
return handleNoMatch(handlerMethods.keySet(), lookupPath, request);
}
}
这里出现了两个集合，urlMap 和 handlerMethods ，urlMap 存储的是url和RequestMappingInfo的映射关系，handlerMethods 存储的是RequestMappingInfo和HandlerMethod的关系。
这里的代码比较复杂，先是从 urlMap中根据url拿到RequestMappingInfo集合然后，如果没获取到即：matches.isEmpty()就会调用addMatchingMappings去处理，有兴趣自己去断点一下，该方法的大致流程如下
- 根据request中的url，method，参数params，请求头headers，consumes，produces去创建一个requestMppingInfo
- 然后根据requestMppingInfo为key从handlerMethods拿到HandlerMethod封装成Match 对象添加到matches集合中
- 从Match 中拿到当前请求对应的HandlerMethod
那么这里的handlerMethods和urlMap 是哪儿来的？
以：RequestMappingHandlerMapping为例在其父类AbstractHandlerMethodMapping中维护了一个 Map<T, HandlerMethod> handlerMethods = new LinkedHashMap<T, HandlerMethod>()该集合中装的就是RequestMappingInfo和HandlerMethod的映射关系，RequestMappingInfo是的RequstMapping的封装，HandlerMethod是对Conroller中方法的封装。初始化流程如下
- AbstractHandlerMethodMapping它实现了InitializingBean接口，在RequestMappingHandlerMapping初始化的使用会触发AbstractHandlerMethodMapping#
afterPropertiesSet方法 - 该方法中会调用AbstractHandlerMethodMapping#initHandlerMethods 初始化HandlerMethod，
其实就是从容器中拿到所有标识了@Controller或者@RequestMapping注解的Bean，也就是controller,然后拿到其中的所有method封装成HandlerMethod对象,然后再拿到method上RequestMapping信息封装成RquestMappingInfo对象，再把RquestMappingInfo和HandlerMethod以前者为key,后置为value注册到handlerMethods集合中。 - 把Url路径和RequestMappingInfo的映射关系存储到AbstractHandlerMethodMapping类中的
MultiValueMap<String, T> urlMap = new LinkedMultiValueMap<String, T>()集合中
这个是在MappingHandlerMapping初始化的时候就把HandlerMethod封装好存储在了handlerMethods 集合中，当请求过来就根据Request去匹配一个RequestMappingInfo，然后再找到对应的HandlerMethod返回。
查找HandlerAdapter
查找HandlerAdapter在org.springframework.web.servlet.DispatcherServlet#getHandlerAdapter中,
protected HandlerAdapter getHandlerAdapter(Object handler) throws ServletException {
for (HandlerAdapter ha : this.handlerAdapters) {
if (logger.isTraceEnabled()) {
logger.trace("Testing handler adapter [" + ha + "]");
}
if (ha.supports(handler)) {
return ha;
}
}
throw new ServletException("No adapter for handler [" + handler +
"]: The DispatcherServlet configuration needs to include a HandlerAdapter that supports this handler");
}
// org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter#supports
public final boolean supports(Object handler) {
return handler instanceof HandlerMethod && supportsInternal((HandlerMethod) handler);
}
从handlerAdapters循环所有的HandlerAdapter，调用supports方法判断是否支持该Handler,如果支持就返回HandlerAdapter
调用拦截器的preHandle
代码在org.springframework.web.servlet.HandlerExecutionChain#applyPreHandle方法中,在HandlerExecutionChain维护了一个HandlerInterceptor[] interceptors，存储了所有的拦截器。源码如下
public class HandlerExecutionChain {
private static final Log logger = LogFactory.getLog(HandlerExecutionChain.class);
private final Object handler;
//拦截器数组
private HandlerInterceptor[] interceptors;
...省略...
boolean applyPreHandle(HttpServletRequest request, HttpServletResponse response) throws Exception {
if (getInterceptors() != null) {
for (int i = 0; i < getInterceptors().length; i++) {
//拿到所有的拦截器，调用preHandle方法
HandlerInterceptor interceptor = getInterceptors()[i];
if (!interceptor.preHandle(request, response, this.handler)) {
//如果拦截器返回false，即不放行就执行拦截器的afterCompletion方法
triggerAfterCompletion(request, response, null);
return false;
}
this.interceptorIndex = i;
}
}
return true;
}
调用HandlerAdatapter
找到HanlderMethod之后执行拦截器的preHandler方法，然后执行HandlerAdapter#handle,最终会调用RequestMappingHandlerAdapter#invokeHandleMethod
private ModelAndView invokeHandleMethod(HttpServletRequest request,
HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {
//把request和response包装到ServletWebRequest对象
ServletWebRequest webRequest = new ServletWebRequest(request, response);
WebDataBinderFactory binderFactory = getDataBinderFactory(handlerMethod);
ModelFactory modelFactory = getModelFactory(handlerMethod, binderFactory);
ServletInvocableHandlerMethod requestMappingMethod = createRequestMappingMethod(handlerMethod, binderFactory);
//ModelAndvView的容器对象，方法调用之后的view和model就会在该容器中
ModelAndViewContainer mavContainer = new ModelAndViewContainer();
mavContainer.addAllAttributes(RequestContextUtils.getInputFlashMap(request));
modelFactory.initModel(webRequest, mavContainer, requestMappingMethod);
mavContainer.setIgnoreDefaultModelOnRedirect(this.ignoreDefaultModelOnRedirect);
AsyncWebRequest asyncWebRequest = WebAsyncUtils.createAsyncWebRequest(request, response);
asyncWebRequest.setTimeout(this.asyncRequestTimeout);
final WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
asyncManager.setTaskExecutor(this.taskExecutor);
asyncManager.setAsyncWebRequest(asyncWebRequest);
asyncManager.registerCallableInterceptors(this.callableInterceptors);
asyncManager.registerDeferredResultInterceptors(this.deferredResultInterceptors);
if (asyncManager.hasConcurrentResult()) {
Object result = asyncManager.getConcurrentResult();
mavContainer = (ModelAndViewContainer) asyncManager.getConcurrentResultContext()[0];
asyncManager.clearConcurrentResult();
if (logger.isDebugEnabled()) {
logger.debug("Found concurrent result value [" + result + "]");
}
requestMappingMethod = requestMappingMethod.wrapConcurrentResult(result);
}
//调用HandlerMethod方法,底层回从HandlerMethod拿到Method,,然后使用反射进行调用
//把方法返回的viewName和model添加到mavContainer
requestMappingMethod.invokeAndHandle(webRequest, mavContainer);
if (asyncManager.isConcurrentHandlingStarted()) {
return null;
}
//获取ModelAndView,从mavContainer拿到viewName和model生成ModelAndView
return getModelAndView(mavContainer, modelFactory, webRequest);
}
invokeAndHandle底层调用该方法nvocableHandlerMethod#invokeForRequest
public final Object invokeForRequest(NativeWebRequest request,
ModelAndViewContainer mavContainer,
Object... providedArgs) throws Exception {
//获取方法的参数
Object[] args = getMethodArgumentValues(request, mavContainer, providedArgs);
if (logger.isTraceEnabled()) {
StringBuilder builder = new StringBuilder("Invoking [");
builder.append(this.getMethod().getName()).append("] method with arguments ");
builder.append(Arrays.asList(args));
logger.trace(builder.toString());
}
//传入参数，调用方法
Object returnValue = invoke(args);
if (logger.isTraceEnabled()) {
logger.trace("Method [" + this.getMethod().getName() + "] returned [" + returnValue + "]");
}
return returnValue;
}
private Object invoke(Object... args) throws Exception {
ReflectionUtils.makeAccessible(this.getBridgedMethod());
try {
//反射调用方法
return getBridgedMethod().invoke(getBean(), args);
}
catch (IllegalArgumentException e) {
String msg = getInvocationErrorMessage(e.getMessage(), args);
throw new IllegalArgumentException(msg, e);
}
catch (InvocationTargetException e) {
// Unwrap for HandlerExceptionResolvers ...
Throwable targetException = e.getTargetException();
if (targetException instanceof RuntimeException) {
throw (RuntimeException) targetException;
}
else if (targetException instanceof Error) {
throw (Error) targetException;
}
else if (targetException instanceof Exception) {
throw (Exception) targetException;
}
else {
String msg = getInvocationErrorMessage("Failed to invoke controller method", args);
throw new IllegalStateException(msg, targetException);
}
}
}
viewResolver渲染视图
handler调用完成之后，代码来到DispatcherServlet#processDispatchResult负责处理结果
private void processDispatchResult(HttpServletRequest request, HttpServletResponse response,
HandlerExecutionChain mappedHandler, ModelAndView mv, Exception exception) throws Exception {
boolean errorView = false;
if (exception != null) {
if (exception instanceof ModelAndViewDefiningException) {
logger.debug("ModelAndViewDefiningException encountered", exception);
mv = ((ModelAndViewDefiningException) exception).getModelAndView();
}
else {
//这里在调用handlerExceptionResolvers处理异常，会循环所有的handlerExceptionResolvers
//然后根据exception生成一个ModelAndView
Object handler = (mappedHandler != null ? mappedHandler.getHandler() : null);
mv = processHandlerException(request, response, handler, exception);
errorView = (mv != null);
}
}
// Did the handler return a view to render?
if (mv != null && !mv.wasCleared()) {
//【重要】渲染视图
render(mv, request, response);
if (errorView) {
WebUtils.clearErrorRequestAttributes(request);
}
}
else {
if (logger.isDebugEnabled()) {
logger.debug("Null ModelAndView returned to DispatcherServlet with name '" + getServletName() +
"': assuming HandlerAdapter completed request handling");
}
}
if (WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {
// Concurrent handling started during a forward
return;
}
if (mappedHandler != null) {
//[重要]执行拦截器的interceptor.afterCompletion
mappedHandler.triggerAfterCompletion(request, response, null);
}
}
代码来到org.springframework.web.servlet.DispatcherServlet#render，该方法负责渲染视图
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.resolveLocale(request);
response.setLocale(locale);
View view;
if (mv.isReference()) {
// We need to resolve the view name.
//调用视图解析器，解析viewName，得到View对象
view = resolveViewName(mv.getViewName(), 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.isDebugEnabled()) {
logger.debug("Rendering view [" + view + "] in DispatcherServlet with name '" + getServletName() + "'");
}
//【重要】调用view.render渲染视图
view.render(mv.getModelInternal(), request, response);
}
protected View resolveViewName(String viewName, Map<String, Object> model, Locale locale,
HttpServletRequest request) throws Exception {
//调用视图解析器，根据viewName生产一个View
for (ViewResolver viewResolver : this.viewResolvers) {
View view = viewResolver.resolveViewName(viewName, locale);
if (view != null) {
return view;
}
}
return null;
}
resolveViewName方法循环所有的viewResolvers ，调用viewResolver.resolveViewName根据viewName解析一个View对象，底层调用AbstractCachingViewResolver#resolveViewName创建View，如下
protected AbstractUrlBasedView buildView(String viewName) throws Exception {
AbstractUrlBasedView view = (AbstractUrlBasedView) BeanUtils.instantiateClass(getViewClass());
//前缀+viewName+后缀
view.setUrl(getPrefix() + viewName + getSuffix());
String contentType = getContentType();
if (contentType != null) {
view.setContentType(contentType);
}
view.setRequestContextAttribute(getRequestContextAttribute());
view.setAttributesMap(getAttributesMap());
if (this.exposePathVariables != null) {
view.setExposePathVariables(exposePathVariables);
}
return view;
}
找到View之后，会调用View的render方法渲染视图，见：org.springframework.web.servlet.view.AbstractView#render
public void render(Map<String, ?> model, HttpServletRequest request, HttpServletResponse response) throws Exception {
if (logger.isTraceEnabled()) {
logger.trace("Rendering view with name '" + this.beanName + "' with model " + model +
" and static attributes " + this.staticAttributes);
}
//拿到model数据模型
Map<String, Object> mergedModel = createMergedOutputModel(model, request, response);
prepareResponse(request, response);
//渲染
renderMergedOutputModel(mergedModel, request, response);
}
继续跟踪org.springframework.web.servlet.view.InternalResourceView#renderMergedOutputModel方法
protected void renderMergedOutputModel(
Map<String, Object> model, HttpServletRequest request, HttpServletResponse response) throws Exception {
// Determine which request handle to expose to the RequestDispatcher.
HttpServletRequest requestToExpose = getRequestToExpose(request);
// Expose the model object as request attributes.
//暴露model对象，把model中的数据设置为request的属性
exposeModelAsRequestAttributes(model, requestToExpose);
// Expose helpers as request attributes, if any.
exposeHelpers(requestToExpose);
// Determine the path for the request dispatcher.
//视图中的模板地址 如：WEB-INF/XX.JSP
String dispatcherPath = prepareForRendering(requestToExpose, response);
// Obtain a RequestDispatcher for the target resource (typically a JSP).
//获取目标资源的RequestDispatcher（通常是JSP）。
RequestDispatcher rd = getRequestDispatcher(requestToExpose, 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.
//如果已included或已提交响应，请执行include，否则forward。
if (useInclude(requestToExpose, response)) {
response.setContentType(getContentType());
if (logger.isDebugEnabled()) {
logger.debug("Including resource [" + getUrl() + "] in InternalResourceView '" + getBeanName() + "'");
}
rd.include(requestToExpose, response);
}
else {
// Note: The forwarded resource is supposed to determine the content type itself.
exposeForwardRequestAttributes(requestToExpose);
if (logger.isDebugEnabled()) {
logger.debug("Forwarding to resource [" + getUrl() + "] in InternalResourceView '" + getBeanName() + "'");
}
//执行forward
rd.forward(requestToExpose, response);
}
}
最后总结一个流程图
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