初始化阶段 ---> 运行（调用）阶段
源码分析
一、初始化阶段
1. 根据配置得知，在DispatcherServlet里没找到init方法，然后在它的父类HttpServletBean找到了init方法的入口，进入HttpServletBean的init()方法
public final void init() throws ServletException {
//去掉了if判断
// Set bean properties from init parameters.
PropertyValues pvs = new ServletConfigPropertyValues(getServletConfig(), this.requiredProperties);
if (!pvs.isEmpty()) {
try {
//定位资源
BeanWrapper bw = PropertyAccessorFactory.forBeanPropertyAccess(this);
//加载配置信息
ResourceLoader resourceLoader = new ServletContextResourceLoader(getServletContext());
bw.registerCustomEditor(Resource.class, new ResourceEditor(resourceLoader, getEnvironment()));
initBeanWrapper(bw);
bw.setPropertyValues(pvs, true);
}
catch (BeansException ex) {
if (logger.isErrorEnabled()) {
logger.error("Failed to set bean properties on servlet '" + getServletName() + "'", ex);
}
throw ex;
}
}
// Let subclasses do whatever initialization they like.
initServletBean();//Ctrl+Alt+B 选择 FrameworkServlet
//去掉了if判断
}
2.在initServletBean()上，按住Ctrl+Alt+B，选择FrameworkServlet进入FrameworkServlet的initServletBean方法
@Override
protected final void initServletBean() throws ServletException {
getServletContext().log("Initializing Spring FrameworkServlet '" + getServletName() + "'");
//去掉了if判断
long startTime = System.currentTimeMillis();
try {
this.webApplicationContext = initWebApplicationContext();//Ctrl + 鼠标左键
initFrameworkServlet();
}
//去掉了catch块，和下面的if判断
}
3. 在 initWebApplicationContext() 方法上，按住 Ctrl+鼠标左键进入initWebApplicationContext方法
protected WebApplicationContext initWebApplicationContext() {
WebApplicationContext rootContext =
WebApplicationContextUtils.getWebApplicationContext(getServletContext());
WebApplicationContext wac = null;
if (this.webApplicationContext != null) {
// A context instance was injected at construction time -> use it
wac = this.webApplicationContext;
if (wac instanceof ConfigurableWebApplicationContext) {
ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) wac;
if (!cwac.isActive()) {
// The context has not yet been refreshed -> provide services such as
// setting the parent context, setting the application context id, etc
if (cwac.getParent() == null) {
// The context instance was injected without an explicit parent -> set
// the root application context (if any; may be null) as the parent
cwac.setParent(rootContext);
}
configureAndRefreshWebApplicationContext(cwac);//支线（会进入SpringIOC的定位阶段）
}
}
}
if (wac == null) {
//在构建时没有注入上下文实例——>查看是否有一个已经在servlet上下文中注册。
//如果存在，则假定已经设置了父上下文(如果有)，
//并且用户已经执行了任何初始化，例如设置上下文id
wac = findWebApplicationContext();
}
if (wac == null) {
//没有为这个servlet定义上下文实例——>创建一个本地实例
wac = createWebApplicationContext(rootContext);
}
if (!this.refreshEventReceived) {
// Either the context is not a ConfigurableApplicationContext with refresh
// support or the context injected at construction time had already been
// refreshed -> trigger initial onRefresh manually here.
onRefresh(wac); //Ctrl+Alt+B 选择 DispatcherServlet
}
if (this.publishContext) {
// Publish the context as a servlet context attribute.
String attrName = getServletContextAttributeName();
getServletContext().setAttribute(attrName, wac);
if (this.logger.isDebugEnabled()) {
this.logger.debug("Published WebApplicationContext of servlet '" + getServletName() +
"' as ServletContext attribute with name [" + attrName + "]");
}
}
return wac;
}
4. 若走configureAndRefreshWebApplicationContext方法，会进入Spring IOC 定位阶段，这里不展开，在onRefresh方法上，按住Ctrl+Alt+B 选择进入DispatcherServlet的onRefresh方法
@Override
protected void onRefresh(ApplicationContext context) {
initStrategies(context);//Ctrl+鼠标左键
}
5. 在initStrategies方法上，按住Ctrl+鼠标左键，进入自身的initStrategies方法，初始化九大策略
protected void initStrategies(ApplicationContext context) {
//多文件上传的组件
initMultipartResolver(context);
//初始化本地语言环境
initLocaleResolver(context);
//初始化模板处理器
initThemeResolver(context);
//handlerMapping
initHandlerMappings(context);
//初始化参数适配器
initHandlerAdapters(context);
//初始化异常拦截器
initHandlerExceptionResolvers(context);
//初始化视图预处理器
initRequestToViewNameTranslator(context);
//初始化视图转换器
initViewResolvers(context);
//初始化Flash管理器
initFlashMapManager(context);
}
二、运行（调用）阶段
运行（调用）阶段，核心方法是DispatcherServlet的doServlet()，核心逻辑由doDispatch()实现 6. 初始化完成后，进入运行（调用）阶段，进入DispatcherServlet的doServlet()
protected void doService(HttpServletRequest request, HttpServletResponse response) throws Exception {
//去掉了if判断以及request赋值
try {
doDispatch(request, response);
}
finally {
if (!WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {
// Restore the original attribute snapshot, in case of an include.
if (attributesSnapshot != null) {
restoreAttributesAfterInclude(request, attributesSnapshot);
}
}
}
}
7. 在doDispatch() 方法上，按住Ctrl+鼠标左键进入自身的doDispatch方法
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 {
// 1.检查是否是文件上传的请求
processedRequest = checkMultipart(request);
multipartRequestParsed = (processedRequest != request);
// Determine handler for the current request.
// 2.取得处理当前请求的controller,这里也称为hanlder,处理器,
// 第一个步骤的意义就在这里体现了.这里并不是直接返回controller,
// 而是返回的HandlerExecutionChain请求处理器链对象,
// 该对象封装了handler和interceptors.
mappedHandler = getHandler(processedRequest);
// 如果handler为空,则返回404
if (mappedHandler == null) {
noHandlerFound(processedRequest, response);
return;
}
// Determine handler adapter for the current request.
//3. 获取处理request的处理器适配器handler adapter
HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());
// Process last-modified header, if supported by the handler.
// 处理 last-modified 请求头
String method = request.getMethod();
boolean isGet = "GET".equals(method);
if (isGet || "HEAD".equals(method)) {
long lastModified = ha.getLastModified(request, mappedHandler.getHandler());
if (logger.isDebugEnabled()) {
logger.debug("Last-Modified value for [" + getRequestUri(request) + "] is: " + lastModified);
}
if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
return;
}
}
if (!mappedHandler.applyPreHandle(processedRequest, response)) {//支线
return;
}
// Actually invoke the handler.
// 4.实际的处理器处理请求,返回结果视图对象
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
if (asyncManager.isConcurrentHandlingStarted()) {
return;
}
// 结果视图对象的处理
applyDefaultViewName(processedRequest, mv);
mappedHandler.applyPostHandle(processedRequest, response, mv);//支线
}
catch (Exception ex) {
dispatchException = ex;
}
catch (Throwable err) {
// As of 4.3, we're processing Errors thrown from handler methods as well,
// making them available for @ExceptionHandler methods and other scenarios.
dispatchException = new NestedServletException("Handler dispatch failed", err);
}
processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);//主线
}
catch (Exception ex) {
triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
}
catch (Throwable err) {
triggerAfterCompletion(processedRequest, response, mappedHandler,
new NestedServletException("Handler processing failed", err));
}
finally {
if (asyncManager.isConcurrentHandlingStarted()) {
// Instead of postHandle and afterCompletion
if (mappedHandler != null) {
// 请求成功响应之后的方法
mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
}
}
else {
// Clean up any resources used by a multipart request.
if (multipartRequestParsed) {
cleanupMultipart(processedRequest);
}
}
}
}
8. 在getHandler方法上，按住Ctrl+鼠标左键进入getHandler方法后，返回的是HandlerExecutionChain
protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
if (this.handlerMappings != null) {
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;
}
9. Ctrl+Alt+键盘左键头返回到第7步，在applyPreHandle方法上，按住Ctrl+Alt+B进入HandlerExecutionChain的applyPreHandle方法
boolean applyPreHandle(HttpServletRequest request, HttpServletResponse response) throws Exception {
HandlerInterceptor[] interceptors = getInterceptors();
if (!ObjectUtils.isEmpty(interceptors)) {
for (int i = 0; i < interceptors.length; i++) {
HandlerInterceptor interceptor = interceptors[i];
if (!interceptor.preHandle(request, response, this.handler)) {
triggerAfterCompletion(request, response, null);
return false;
}
this.interceptorIndex = i;
}
}
return true;
}
10. 在preHandle方法上，按Ctrl+Alt+B进入HandlerInterceptor的preHandle方法，默认返回true。 preHandle是handle的前置处理
default boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler)
throws Exception {
return true;
}
11. 按住Ctrl+Alt+键盘左键头返回到第7步，在handle方法上，按住Ctrl+Alt+B，进入AbstractHandlerMethodAdapter的handle方法
public final ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)
throws Exception {
return handleInternal(request, response, (HandlerMethod) handler);
}
12. 在handleInternal方法上，按住Ctrl+Alt+B进入RequestMappingHandlerAdapter的handleInternal方法
protected ModelAndView handleInternal(HttpServletRequest request,
HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {
ModelAndView mav;
checkRequest(request);
// 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) {
mav = invokeHandlerMethod(request, response, handlerMethod);
}
}
else {
// No HttpSession available -> no mutex necessary
mav = invokeHandlerMethod(request, response, handlerMethod);
}
}
else {
// No synchronization on session demanded at all...
mav = invokeHandlerMethod(request, response, handlerMethod);
}
if (!response.containsHeader(HEADER_CACHE_CONTROL)) {
if (getSessionAttributesHandler(handlerMethod).hasSessionAttributes()) {
applyCacheSeconds(response, this.cacheSecondsForSessionAttributeHandlers);
}
else {
prepareResponse(response);
}
}
return mav;
}
13. 在invokeHandlerMethod方法上，按住Ctrl+鼠标左键进入自身的invokeHandlerMethod方法
protected ModelAndView invokeHandlerMethod(HttpServletRequest request,
HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {
//去掉了if判断和finally
return getModelAndView(mavContainer, modelFactory, webRequest);
}
14. 在getModelAndView方法上，按住Ctrl+鼠标左键进入自身的getModelAndView方法，返回ModelAndView
private ModelAndView getModelAndView(ModelAndViewContainer mavContainer,
ModelFactory modelFactory, NativeWebRequest webRequest) throws Exception {
modelFactory.updateModel(webRequest, mavContainer);
if (mavContainer.isRequestHandled()) {
return null;
}
ModelMap model = mavContainer.getModel();
ModelAndView mav = new ModelAndView(mavContainer.getViewName(), model, mavContainer.getStatus());
if (!mavContainer.isViewReference()) {
mav.setView((View) mavContainer.getView());
}
if (model instanceof RedirectAttributes) {
Map<String, ?> flashAttributes = ((RedirectAttributes) model).getFlashAttributes();
HttpServletRequest request = webRequest.getNativeRequest(HttpServletRequest.class);
if (request != null) {
RequestContextUtils.getOutputFlashMap(request).putAll(flashAttributes);
}
}
return mav;
}
15. 按住Ctrl+Alt+键盘左键头返回到第7步，在applyPostHandle方法上，按住Ctrl+鼠标左键，进入HandlerExecutionChain的applyPostHandle方法
void applyPostHandle(HttpServletRequest request, HttpServletResponse response, @Nullable ModelAndView mv)
throws Exception {
HandlerInterceptor[] interceptors = getInterceptors();
if (!ObjectUtils.isEmpty(interceptors)) {
for (int i = interceptors.length - 1; i >= 0; i--) {
HandlerInterceptor interceptor = interceptors[i];
interceptor.postHandle(request, response, this.handler, mv);
}
}
}
16. 在postHandle方法上，按住Ctrl+Alt+B，选择HandlerInterceptor，进入到HandlerInterceptor的postHandle方法，postHandle方法为handle的后置方法
default void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler,
@Nullable ModelAndView modelAndView) throws Exception {
}
17. 按住Ctrl+Alt+键盘左键头返回到第7步，在processDispatchResult方法上，按住Ctrl+鼠标左键进入processDispatchResult方法
private void processDispatchResult(HttpServletRequest request, HttpServletResponse response,
@Nullable HandlerExecutionChain mappedHandler, @Nullable ModelAndView mv,
@Nullable 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);//Ctrl+鼠标左键
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);
}
}
18. 在render方法上，按住Ctrl+鼠标左键进入自身的render方法
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);
View view;
String viewName = mv.getViewName();
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.isDebugEnabled()) {
logger.debug("Rendering view [" + view + "] in DispatcherServlet with name '" + getServletName() + "'");
}
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 + "] in DispatcherServlet with name '" +
getServletName() + "'", ex);
}
throw ex;
}
}
19. 在render方法上，按住Ctrl+Alt+B，选择的AbstractView，进入AbstractView的render方法，完成运行（调用）阶段。
public void render(@Nullable 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);
}
Map<String, Object> mergedModel = createMergedOutputModel(model, request, response);
prepareResponse(request, response);
renderMergedOutputModel(mergedModel, getRequestToExpose(request), response);
}