springmvc的执行过程的源码分析

1.前端控制器接收请求，调用doDispatch方法。

/**
* Process the actual dispatching to the handler.
* <p>The handler will be obtained by applying the servlet's HandlerMappings in order.
* The HandlerAdapter will be obtained by querying the servlet's installed HandlerAdapters
* to find the first that supports the handler class.
* <p>All HTTP methods are handled by this method. It's up to HandlerAdapters or handlers
* themselves to decide which methods are acceptable.
* @param request current HTTP request
* @param response current HTTP response
* @throws Exception in case of any kind of processing failure
*/
protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
HttpServletRequest processedRequest = request;
HandlerExecutionChain mappedHandler = null;
boolean multipartRequestParsed = false;

WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);

try {
ModelAndView mv = null;
Exception dispatchException = null;

try {
//先检查是不是Multipart类型的，比如上传等，如果是Multipart类型的，则转换为MultipartHttpServletRequest类型
processedRequest = checkMultipart(request);
multipartRequestParsed = (processedRequest != request);

//获取当前请求的Handler
mappedHandler = getHandler(processedRequest);
if (mappedHandler == null || mappedHandler.getHandler() == null) {
noHandlerFound(processedRequest, response);
return;
}

//获取当前请求的处理器适配器
HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());

String method = request.getMethod();
boolean isGet = "GET".equals(method);
if (isGet || "HEAD".equals(method)) {
long lastModified = ha.getLastModified(request, mappedHandler.getHandler());
if (logger.isDebugEnabled()) {

4000
logger.debug("Last-Modified value for [" + getRequestUri(request) + "] is: " + lastModified);
}
if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
return;
}
}

if (!mappedHandler.applyPreHandle(processedRequest, response)) {
return;
}

//执行处理器
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

if (asyncManager.isConcurrentHandlingStarted()) {
return;
}

//处理成默认视图名，就是添加前缀和后缀等
applyDefaultViewName(processedRequest, mv);
mappedHandler.applyPostHandle(processedRequest, response, mv);
}
catch (Exception ex) {
dispatchException = ex;
}

//处理最后的结果，进行视图渲染
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
if (mappedHandler != null) {
mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
}
}
else {
// Clean up any resources used by a multipart request.
if (multipartRequestParsed) {
cleanupMultipart(processedRequest);
}
}
}
}

2.执行doDispatch方法中的getHandler方法获得处理器链。

// Determine handler for the current request.
mappedHandler = getHandler(processedRequest);

getHandler方法的代码：

/**
* Return the HandlerExecutionChain for this request.
* <p>Tries all handler mappings in order.
* @param request current HTTP request
* @return the HandlerExecutionChain, or {@code null} if no handler could be found
*/
protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
//循环所有已注册的HandlerMapping(处理器映射)
for (HandlerMapping hm : this.handlerMappings) {
if (logger.isTraceEnabled()) {
logger.trace(
"Testing handler map [" + hm + "] in DispatcherServlet with name '" + getServletName() + "'");
}
HandlerExecutionChain handler = hm.getHandler(request);
if (handler != null) {
return handler;
}
}
return null;
}

hm.getHandler(request)的代码为：

public final HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
//根据请求获取处理器
Object handler = getHandlerInternal(request);
if (handler == null) {
//如果没有找到就使用默认的处理器        handler = getDefaultHandler();
}
if (handler == null) {
return null;
}
//如果处理器是String类型，则表明是它是一个bean名称
if (handler instanceof String) {
String handlerName = (String) handler;
//根据这bean名称获取bean
handler = getApplicationContext().getBean(handlerName);
}
//把获取的处理器封装成处理器链
return getHandlerExecutionChain(handler, request);
}

3.获取处理器适配器

HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());

/**
* Return the HandlerAdapter for this handler object.
* @param handler the handler object to find an adapter for
* @throws ServletException if no HandlerAdapter can be found for the handler. This is a fatal error.
*/
protected HandlerAdapter getHandlerAdapter(Object handler) throws ServletException {
//遍历所有的处理器适配器
for (HandlerAdapter ha : this.handlerAdapters) {
if (logger.isTraceEnabled()) {
logger.trace("Testing handler adapter [" + ha + "]");
}
//找到和当前处理器匹配的处理器适配器
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");
}

4.使用处理器适配器执行处理器获得ModelAndView

mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

不同的处理器适配器有不同的实现，例如RequestMappingHandlerAdapter：

首先进入AbstractHandlerMethodAdapter的handle方法

@Override
public final ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)
throws Exception {

return handleInternal(request, response, (HandlerMethod) handler);
}

handleInternal在RequestMappingHandlerAdapter中：

@Override
protected ModelAndView handleInternal(HttpServletRequest request,
HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {

checkRequest(request);

if (getSessionAttributesHandler(handlerMethod).hasSessionAttributes()) {
applyCacheSeconds(response, this.cacheSecondsForSessionAttributeHandlers);
}
else {
prepareResponse(response);
}

// Execute invokeHandlerMethod in synchronized block if required.
if (this.synchronizeOnSession) {
HttpSession session = request.getSession(false);
if (session != null) {
Object mutex = WebUtils.getSessionMutex(session);
synchronized (mutex) {
return invokeHandlerMethod(request, response, handlerMethod);
}
}
}

return invokeHandlerMethod(request, response, handlerMethod);
}

5.进行视图渲染，将model的数据填充到request

执行doDispatch方法中的processDispatchResult方法。

/**
* 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 {

boolean errorView = false;

if (exception != null) {
if (exception instanceof ModelAndViewDefiningException) {
logger.debug("ModelAndViewDefiningException encountered", exception);
mv = ((ModelAndViewDefiningException) exception).getModelAndView();
}
else {
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()) {
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) {
mappedHandler.triggerAfterCompletion(request, response, null);
}
}

在render方法中进行渲染。

/**
* 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.resolveLocale(request);
response.setLocale(locale);

View view;
if (mv.isReference()) {
// We need to resolve the view name.
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 '
aff7
" + getServletName() + "'");
}
}

// Delegate to the View object for rendering.
if (logger.isDebugEnabled()) {
logger.debug("Rendering view [" + view + "] in DispatcherServlet with name '" + getServletName() + "'");
}
try {
view.render(mv.getModelInternal(), request, response);
}
catch (Exception ex) {
if (logger.isDebugEnabled()) {
logger.debug("Error rendering view [" + view + "] in DispatcherServlet with name '" +
getServletName() + "'", ex);
}
throw ex;
}
}