DispatcherServlet前端控制器
配置
DispatcherServlet充当SpringMVC的前端控制器，整个流程控制的中心，控制其它组件执行，统一调度，降低组件之间的耦合性，提高每个组件的扩展性。与其他Servlet一样，DispatcherServlet必须在Web应用程序的web.xml文件中进行配置
web.xml配置
<!-- springmvc会过滤掉.html的 导致视图解析器无法找到
如果只是使用jsp资源而未使用html的话可以不配置该项
-->
<servlet-mapping>
<servlet-name>default</servlet-name>
<url-pattern>*.html</url-pattern>
</servlet-mapping>
<!-- 配置DispatcherServlet -->
<servlet>
<servlet-name>DispatcherServlet</servlet-name>
<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
<!-- 初始化参数：配置Springmvc配置文件的位置和名称
默认配置文件为：/WEB-INF/<servlet-name>-servlet.xml
-->
<init-param>
<param-name>contextConfigLocation</param-name>
<param-value>classpath:springmvc.xml</param-value>
</init-param>
<!-- 指定servlet加载顺序，指定的话，tomcat在容器启动的时候就会初始化并加载servlet实例，值越小，越早加载；如果不指定该值，表示调用servlet请求时在初始化并加载servlet实例 -->
<!-- 在程序启动的时候根据contextConfigLocation配置的xml文件开始配置spring应用上下文，初始化组件 -->
<load-on-startup>1</load-on-startup>
</servlet>
<servlet-mapping>
<servlet-name>DispatcherServlet</servlet-name>
<!-- url-pattern匹配：
精确匹配：/a
目录匹配：/*
扩展名匹配：*.do
默认匹配：/
这里要配置为/，使之所有在web.xml中找不到匹配元素的url，都会交给DispatcherServlet来处理
-->
<url-pattern>/</url-pattern>
</servlet-mapping>
<!-- 处理静态资源 -->
<mvc:resources mapping="/images/**" location="/images/" cache-period="31556926"></mvc:resources>
<mvc:resources mapping="/js/**" location="/js/" cache-period="31556926"></mvc:resources>
<mvc:resources mapping="/css/**" location="/css/" cache-period="31556926"></mvc:resources>
serlvet3.0扩展
在servlet3.0中，可以不使用xml配置servlet，容器会在类路径中查找实现ServletContainerInitializer接口的类，会使用它来配置Servlet容器，在spring中提供了该接口的实现SpringServletContainerInitializer，该实现类会去查找实现WebApplicationInitializer接口的类来完成配置任务，AbstractAnnotationConfigDispatcherServletInitializer就是该接口的基础实现，可以通过继承AbstractAnnotationConfigDispatcherServletInitializer类来进行配置DispatcherServlet
WebApplicationInitializer的作用就类似于web.xml，项目启动时会自动执行onStartup方法
需要实现三个方法
// 将一个或多个路径映射到DispacherServlet
protected abstract String[] getServletMappings();
// 返回带有@Configuration注解的类用来定义ContextLoaderLister创建应用上下文中的bean
protected abstract Class<?>[] getRootConfigClasses();
// 返回带有@Configuration注解的类用来定义DispacherServlet应用上下文中的bean
protected abstract Class<?>[] getServletConfigClasses();
静态资源请求问题
因为DispatcherServlet的<url-pattern>配置的是/，针对的是所有请求，对于一些的静态资源(如.js、.css)等也会经过DispatcherServlet，但是DispatcherServlet是处理动态请求的，无法处理静态资源
可以配置<mvc:default-servlet-handler/>来解决，作用是处理静态资源，会在SpringMVC上下文中定义一个DefaultServletHttpRequestHandle，对进行DispatcherServlet的请求进行筛选，如果发现是没有经过映射的请求，就将请求交给WEB服务器默认的Servlet来处理，否则交由DispatcherServlet来处理
default-servlet-name默认是default，如果不是default需要显式的进行配置(看所使用的web服务器，tomcat是default)
<mvc:default-servlet-handler default-servlet-name="default"/>
需要注意的是，配置了<mvc:default-servlet-handler/>之后，@RequestMapping的映射会失效，需要加上<mvc:annotation-driven/>配置
源码分析
先看一下DispatcherServlet结构，其本质就是一个Servlet
DispatcherServlet的工作大致可以分为两个部分：一是初始化部分，本质就是一个Servlet，在init方法时会进行初始化，最终调用initStrategies方法；二是对于HTTP请求进行响应，调用doGet和doPost方法，最终调用doDispatch方法
初始化
// DispatcherServlet继承了FrameworkServlet类，FrameworkServlet继承了HttpServletBean类，HttpServletBean继承了HttpServlet，所以DispatcherServlet本质上是一个Servlet
public class DispatcherServlet extends FrameworkServlet
public abstract class FrameworkServlet extends HttpServletBean implements ApplicationContextAware
public abstract class HttpServletBean extends HttpServlet implements EnvironmentCapable, EnvironmentAware
HttpServletBean的init方法
public final void init() throws ServletException {
// Set bean properties from init parameters.
// 获取初始化参数 init-param
PropertyValues pvs = new ServletConfigPropertyValues(getServletConfig(), this.requiredProperties);
if (!pvs.isEmpty()) {
try {
// 将当前的servlet类转换为一个BeanWrapper，使得可以用spring的方式来对init-param参数进行注入
BeanWrapper bw = PropertyAccessorFactory.forBeanPropertyAccess(this);
ResourceLoader resourceLoader = new ServletContextResourceLoader(getServletContext());
// 注册自定义属性编辑器
bw.registerCustomEditor(Resource.class, new ResourceEditor(resourceLoader, getEnvironment()));
// 空实现
initBeanWrapper(bw);
// 属性注入
bw.setPropertyValues(pvs, true);
}
catch (BeansException ex) {
throw ex;
}
}
// Let subclasses do whatever initialization they like.
// 调用子类的initServletBean，来进行servletBean的初始化
// org.springframework.web.servlet.FrameworkServlet#initServletBean
initServletBean();
}
FrameworkServlet的initServletBean方法
protected final void initServletBean() throws ServletException {
// 初始化上下文
this.webApplicationContext = initWebApplicationContext();
// 空实现
initFrameworkServlet();
}
// 创建或刷新WebApplicationContext实例并对servlet功能所使用的变量进行初始化
protected WebApplicationContext initWebApplicationContext() {
// 这是父容器，获取根上下文，ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE，是在ContextLoaderListener初始化过程中建立的
WebApplicationContext rootContext =
WebApplicationContextUtils.getWebApplicationContext(getServletContext());
// 这是子容器
WebApplicationContext wac = null;
if (this.webApplicationContext != null) {
// A context instance was injected at construction time -> use it
// 通过构造器创建的实例
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
// 根上下文作为该上下文的双亲上下文
cwac.setParent(rootContext);
}
// 刷新上下文环境
configureAndRefreshWebApplicationContext(cwac);
}
}
}
if (wac == null) {
// No context instance was injected at construction time -> see if one
// has been registered in the servlet context. If one exists, it is assumed
// that the parent context (if any) has already been set and that the
// user has performed any initialization such as setting the context id
// 根据contextAttribute属性从ServletContext中加载WebApplicationContext
wac = findWebApplicationContext();
}
// 通过上述两种方式都没有找到，则说明不存在WebApplicationContext实例，则进行创建
if (wac == null) {
// No context instance is defined for this servlet -> create a local one
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.
// 调用DispatcherServlet#initStrategies方法，初始化DispatcherServlet的默认策略配置
onRefresh(wac);
}
// 把当前创建的上下文存到ServletContext中
if (this.publishContext) {
// Publish the context as a servlet context attribute.
String attrName = getServletContextAttributeName();
getServletContext().setAttribute(attrName, wac);
}
return wac;
}
protected WebApplicationContext createWebApplicationContext(ApplicationContext parent) {
Class<?> contextClass = getContextClass();
if (!ConfigurableWebApplicationContext.class.isAssignableFrom(contextClass)) {
throw new ApplicationContextException(
"Fatal initialization error in servlet with name '" + getServletName() +
"': custom WebApplicationContext class [" + contextClass.getName() +
"] is not of type ConfigurableWebApplicationContext");
}
// contextClass使用的是默认的DEFAULT_CONTEXT_CLASS，XmlWebApplicationContext.class
// 通过反射实例化contextClass
ConfigurableWebApplicationContext wac =
(ConfigurableWebApplicationContext) BeanUtils.instantiateClass(contextClass);
wac.setEnvironment(getEnvironment());
// 配置双亲上下文为传入的根上下文，parent是在ConetextLoderListener中创建的实例
wac.setParent(parent);
wac.setConfigLocation(getContextConfigLocation());
// 初始化spring环境
configureAndRefreshWebApplicationContext(wac);
return wac;
}
配置刷新WebApplicationContext
protected void configureAndRefreshWebApplicationContext(ConfigurableWebApplicationContext wac) {
if (ObjectUtils.identityToString(wac).equals(wac.getId())) {
// The application context id is still set to its original default value
// -> assign a more useful id based on available information
if (this.contextId != null) {
wac.setId(this.contextId);
}
else {
// Generate default id...
wac.setId(ConfigurableWebApplicationContext.APPLICATION_CONTEXT_ID_PREFIX +
ObjectUtils.getDisplayString(getServletContext().getContextPath()) + '/' + getServletName());
}
}
wac.setServletContext(getServletContext());
wac.setServletConfig(getServletConfig());
wac.setNamespace(getNamespace());
// 监听器 该监听器在接收到ContextRefreshedEvent事件后，会调用onRefresh方法完成刷新
wac.addApplicationListener(new SourceFilteringListener(wac, new ContextRefreshListener()));
// The wac environment's #initPropertySources will be called in any case when the context
// is refreshed; do it eagerly here to ensure servlet property sources are in place for
// use in any post-processing or initialization that occurs below prior to #refresh
ConfigurableEnvironment env = wac.getEnvironment();
if (env instanceof ConfigurableWebEnvironment) {
((ConfigurableWebEnvironment) env).initPropertySources(getServletContext(), getServletConfig());
}
postProcessWebApplicationContext(wac);
applyInitializers(wac);
// 加载配置文件，这里就是执行org.springframework.context.support.AbstractApplicationContext#refresh方法，与spring中加载上下文是一样的
wac.refresh();
}
onRefresh
用于刷新spring在web功能实现中所必须使用的全局变量
protected void onRefresh(ApplicationContext context) {
initStrategies(context);
}
// 下边的组件如果没有配置默认会读取org.springframework.web.servlet下的DispatcherServlet.properties
protected void initStrategies(ApplicationContext context) {
// 初始化MultipartResolver，获取beanName为multipartResolver的bean，没有默认值，必须手动配置，用于处理上传请求,处理方法是将普通的request包装成MultipartHttpServletRequest，可以直接调用getFile方法获取File
initMultipartResolver(context);
// 初始化LocaleResolver，获取beanName为localeResolver的bean，如果没有默认DispatcherServlet.properties获取
//国际化解析器，使用的地方有两个，一是ViewResolver视图解析的时候；二是用到国际化资源或者主题的时候。
initLocaleResolver(context);
// 初始化ThemeResolver，获取beanName为themeResolver的bean，如果没有默认DispatcherServlet.properties获取
//用于解析主题。SpringMVC中一个主题对应 一个properties文件，里面存放着跟当前主题相关的所有资源，如图片、css样式等。SpringMVC的主题也支持国际化
initThemeResolver(context);
// 初始化HandlerMappings，如果配置detectAllHandlerMappings为false的话，只会获取beanName为handlerMapping的bean，否则会找所有类型为HandlerMapping的bean，默认是true，如果没有默认DispatcherServlet.properties获取
//初始化处理器映射器
initHandlerMappings(context);
// 初始化HandlerAdapters，如果配置detectAllHandlerAdapters为false的话，只会获取beanName为handlerAdapter的bean，否则会找所有类型为HandlerAdapter的bean，默认是true，如果没有默认DispatcherServlet.properties获取
//初始化处理器适配器
initHandlerAdapters(context);
// 初始化HandlerExceptionResolvers，如果配置detectAllHandlerExceptionResolvers为false的话，只会获取beanName为handlerExceptionResolver的bean，否则会找所有类型为HandlerExceptionResolver的bean，默认是true，如果没有默认DispatcherServlet.properties获取
// 初始化异常处理器，对异常情况进行处理，在SpringMVC中就是HandlerExceptionResolver。
initHandlerExceptionResolvers(context);
// 初始化RequestToViewNameTranslator，获取beanName为viewNameTranslator的bean，如果没有默认DispatcherServlet.properties获取
//有的Handler处理完后并没有设置View也没有设置ViewName，这时就需要RequestToViewNameTranslator从request获取ViewName了
initRequestToViewNameTranslator(context);
// 初始化ViewResolvers，如果配置detectAllViewResolvers为false的话，只会获取beanName为viewResolver的bean，否则会找所有类型为ViewResolver的bean，默认是true，如果没有默认DispatcherServlet.properties获取
//ViewResolver用来将String类型的视图名和Locale解析为View类型的视图。View是用来渲染页面的，也就是将程序返回的参数填入模板里，生成html（也可能是其它类型）文件。
initViewResolvers(context);
// 初始化FlashMapManager，获取beanName为flashMapManager的bean，如果没有默认DispatcherServlet.properties获取
//用来管理FlashMap的，FlashMap主要用在redirect重定向中传递参数。
initFlashMapManager(context);
}
上述默认值是从DispatcherServlet.properties中取的
# 国际化解析器
org.springframework.web.servlet.LocaleResolver=org.springframework.web.servlet.i18n.AcceptHeaderLocaleResolver
# 主题解析器
org.springframework.web.servlet.ThemeResolver=org.springframework.web.servlet.theme.FixedThemeResolver
# HandlerMapping
org.springframework.web.servlet.HandlerMapping=org.springframework.web.servlet.handler.BeanNameUrlHandlerMapping,
org.springframework.web.servlet.mvc.annotation.DefaultAnnotationHandlerMapping
# 处理器适配器
org.springframework.web.servlet.HandlerAdapter=org.springframework.web.servlet.mvc.HttpRequestHandlerAdapter,
org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter,
org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter
# 异常解析器
org.springframework.web.servlet.HandlerExceptionResolver=org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerExceptionResolver,
org.springframework.web.servlet.mvc.annotation.ResponseStatusExceptionResolver,
org.springframework.web.servlet.mvc.support.DefaultHandlerExceptionResolver
# 策略视图名称转换器
org.springframework.web.servlet.RequestToViewNameTranslator=org.springframework.web.servlet.view.DefaultRequestToViewNameTranslator
# 视图解析器
org.springframework.web.servlet.ViewResolver=org.springframework.web.servlet.view.InternalResourceViewResolver
# FlashMap管理器
org.springframework.web.servlet.FlashMapManager=org.springframework.web.servlet.support.SessionFlashMapManager
介绍各个组件
LocaleResolver
国际化处理
-
AcceptHeaderLocaleResolver 基于URL参数的配置，可以读取url中locale=zh_CN来控制国际化参数 -
CookieLocaleResolver 基于cookie的配置，可以通过浏览器的cookie设置获取Locale对象 -
SessionLocaleResolver 基于session的配置，可以公国检验session的预置的属性来解析，如果没有则会根据请求头中的accept-language来确定
ThemeResolver
主题处理，根据主题控制网页风格
-
FixedThemeResolver 选择一个固定的主题 -
CookieThemeResolver 用于实现用户所选的主题，以cookie的形式存放在客户端的机器上 -
SessionThemeResolver 用于主题存放在session中
HandlerAdapter
-
HttpRequestHandlerAdapter 仅支持HTTP请求处理器的适配，将HTTP请求对象和响应对象传递给HTTP请求处理器的实现，不需要返回值，主要应用在基于HTTP的远程调用实现上 -
SimpleControllerHandlerAdapter 将HTTP请求适配到一个控制器的实现进行处理 -
AnnotationMethodHandlerAdapter 在3.2被废弃，使用RequestMappingHandlerAdapter，基于注解的实现
HandlerExceptionResolver
进行异常处理
处理请求
请求过来之后进行统一处理，由service()/doGet()/doPost()等方法调用
// doPost -> processRequest -> doService -> doDispatch
protected final void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
processRequest(request, response);
}
protected final void processRequest(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
long startTime = System.currentTimeMillis();
Throwable failureCause = null;
// 提取当前线程的LocaleContext和RequestAttributes，在请求结束后进行重置
LocaleContext previousLocaleContext = LocaleContextHolder.getLocaleContext();
LocaleContext localeContext = buildLocaleContext(request);
RequestAttributes previousAttributes = RequestContextHolder.getRequestAttributes();
ServletRequestAttributes requestAttributes = buildRequestAttributes(request, response, previousAttributes);
WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
asyncManager.registerCallableInterceptor(FrameworkServlet.class.getName(), new RequestBindingInterceptor());
// 将当前请求的LocaleContext和RequestAttributes绑定到当前线程,LocaleContextHolder和RequestContextHolder中
initContextHolders(request, localeContext, requestAttributes);
try {
// 实际处理请求
doService(request, response);
}
catch (ServletException ex) {
failureCause = ex;
throw ex;
}
catch (IOException ex) {
failureCause = ex;
throw ex;
}
catch (Throwable ex) {
failureCause = ex;
throw new NestedServletException("Request processing failed", ex);
}
finally {
// 请求结束后恢复原始状态
resetContextHolders(request, previousLocaleContext, previousAttributes);
if (requestAttributes != null) {
requestAttributes.requestCompleted();
}
// 发布消息
publishRequestHandledEvent(request, response, startTime, failureCause);
}
}
protected void doService(HttpServletRequest request, HttpServletResponse response) throws Exception {
// Keep a snapshot of the request attributes in case of an include,
// to be able to restore the original attributes after the include.
Map<String, Object> attributesSnapshot = null;
// include请求，对request中的Attribute进行备份
if (WebUtils.isIncludeRequest(request)) {
attributesSnapshot = new HashMap<String, Object>();
Enumeration<?> attrNames = request.getAttributeNames();
while (attrNames.hasMoreElements()) {
String attrName = (String) attrNames.nextElement();
if (this.cleanupAfterInclude || attrName.startsWith(DEFAULT_STRATEGIES_PREFIX)) {
attributesSnapshot.put(attrName, request.getAttribute(attrName));
}
}
}
// Make framework objects available to handlers and view objects.
request.setAttribute(WEB_APPLICATION_CONTEXT_ATTRIBUTE, getWebApplicationContext());
request.setAttribute(LOCALE_RESOLVER_ATTRIBUTE, this.localeResolver);
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));
}
request.setAttribute(OUTPUT_FLASH_MAP_ATTRIBUTE, new FlashMap());
request.setAttribute(FLASH_MAP_MANAGER_ATTRIBUTE, this.flashMapManager);
try {
// 进行请求分发
doDispatch(request, response);
}
finally {
if (!WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {
// Restore the original attribute snapshot, in case of an include.
// 还原request中的Attribute快照
if (attributesSnapshot != null) {
restoreAttributesAfterInclude(request, attributesSnapshot);
}
}
}
}
// 真正的请求处理
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 {
// 检查是不是multipart类型的，如果是会将请求类型转为MultipartHttpServletRequest
processedRequest = checkMultipart(request);
multipartRequestParsed = (processedRequest != request);
// Determine handler for the current request.
// 获取处理当前请求的处理器，根据请求的URL信息去查找匹配的URL的Handler，如果查找成，并返回一个执行链HandlerExecutionChain
mappedHandler = getHandler(processedRequest);
if (mappedHandler == null || mappedHandler.getHandler() == null) {
// 没有找到对应的handler，返回404
noHandlerFound(processedRequest, response);
return;
}
// Determine handler adapter for the current request.
// 根据当前的handler获取对应的HandlerAdapter
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 (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
return;
}
}
// 执行拦截器的preHandler方法，按顺序执行，如果执行过程中有拦截器的preHandler方法返回false，则需要执行拦截器的afterCompletion方法，按照反向顺序进行执行 for (int i = this.interceptorIndex; i >= 0; i--)
if (!mappedHandler.applyPreHandle(processedRequest, response)) {
return;
}
// Actually invoke the handler.
// 调用handler处理器逻辑，即业务代码Controller
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
// 异步处理直接返回
if (asyncManager.isConcurrentHandlingStarted()) {
return;
}
// 如果没有返回view的视图名称，则采用默认的视图名称，添加前缀、后缀
applyDefaultViewName(processedRequest, mv);
// 执行拦截器的postHandle方法，按照反向顺序进行执行 for (int i = interceptors.length - 1; i >= 0; i--)
mappedHandler.applyPostHandle(processedRequest, response, mv);
}
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);
}
// 处理返回结果，包括视图渲染，处理异常，以及拦截器的afterCompletion方法
processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
}
catch (Exception ex) {
// 异常处理，以及拦截器的afterCompletion方法
triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
}
catch (Throwable err) {
triggerAfterCompletion(processedRequest, response, mappedHandler,
new NestedServletException("Handler processing failed", err));
}
finally {
// 异步请求
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.
// 清除multipart上传的资源
if (multipartRequestParsed) {
cleanupMultipart(processedRequest);
}
}
}
}
getHandler
protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
for (HandlerMapping hm : this.handlerMappings) {
HandlerExecutionChain handler = hm.getHandler(request);
if (handler != null) {
return handler;
}
}
return null;
}
这里就以RequestMappingHandlerMapping为例
public final HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
// 获取request对应的handler
Object handler = getHandlerInternal(request);
if (handler == null) {
// 如果没有，则使用默认的handler
handler = getDefaultHandler();
}
if (handler == null) {
return null;
}
// Bean name or resolved handler?
if (handler instanceof String) {
String handlerName = (String) handler;
handler = getApplicationContext().getBean(handlerName);
}
HandlerExecutionChain executionChain = getHandlerExecutionChain(handler, request);
if (CorsUtils.isCorsRequest(request)) {
CorsConfiguration globalConfig = this.globalCorsConfigSource.getCorsConfiguration(request);
CorsConfiguration handlerConfig = getCorsConfiguration(handler, request);
CorsConfiguration config = (globalConfig != null ? globalConfig.combine(handlerConfig) : handlerConfig);
executionChain = getCorsHandlerExecutionChain(request, executionChain, config);
}
return executionChain;
}
ha.handle
通过适配器去调用Handler的实际逻辑，以RequestMappingHandlerAdapter为例
protected ModelAndView handleInternal(HttpServletRequest request,
HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {
ModelAndView mav;
checkRequest(request);
// Execute invokeHandlerMethod in synchronized block if required.
// 如果需要session内的同步执行
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...
// 调用用户逻辑
mav = invokeHandlerMethod(request, response, handlerMethod);
}
if (!response.containsHeader(HEADER_CACHE_CONTROL)) {
if (getSessionAttributesHandler(handlerMethod).hasSessionAttributes()) {
applyCacheSeconds(response, this.cacheSecondsForSessionAttributeHandlers);
}
else {
prepareResponse(response);
}
}
return mav;
}
invokeHandlerMethod
protected ModelAndView invokeHandlerMethod(HttpServletRequest request,
HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {
ServletWebRequest webRequest = new ServletWebRequest(request, response);
try {
// 获取数据绑定 initBinder
WebDataBinderFactory binderFactory = getDataBinderFactory(handlerMethod);
// 获取@SessionAttributes
ModelFactory modelFactory = getModelFactory(handlerMethod, binderFactory);
ServletInvocableHandlerMethod invocableMethod = createInvocableHandlerMethod(handlerMethod);
invocableMethod.setHandlerMethodArgumentResolvers(this.argumentResolvers);
invocableMethod.setHandlerMethodReturnValueHandlers(this.returnValueHandlers);
invocableMethod.setDataBinderFactory(binderFactory);
invocableMethod.setParameterNameDiscoverer(this.parameterNameDiscoverer);
ModelAndViewContainer mavContainer = new ModelAndViewContainer();
mavContainer.addAllAttributes(RequestContextUtils.getInputFlashMap(request));
modelFactory.initModel(webRequest, mavContainer, invocableMethod);
mavContainer.setIgnoreDefaultModelOnRedirect(this.ignoreDefaultModelOnRedirect);
AsyncWebRequest asyncWebRequest = WebAsyncUtils.createAsyncWebRequest(request, response);
asyncWebRequest.setTimeout(this.asyncRequestTimeout);
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();
invocableMethod = invocableMethod.wrapConcurrentResult(result);
}
// 进行方法调用
invocableMethod.invokeAndHandle(webRequest, mavContainer);
if (asyncManager.isConcurrentHandlingStarted()) {
return null;
}
return getModelAndView(mavContainer, modelFactory, webRequest);
}
finally {
webRequest.requestCompleted();
}
}
processDispatchResult处理请求结果
private void processDispatchResult(HttpServletRequest request, HttpServletResponse response,
HandlerExecutionChain mappedHandler, ModelAndView mv, Exception exception) throws Exception {
boolean errorView = false;
// 请求处理过程中有异常抛出
if (exception != null) {
if (exception instanceof ModelAndViewDefiningException) {
mv = ((ModelAndViewDefiningException) exception).getModelAndView();
}
else {
Object handler = (mappedHandler != null ? mappedHandler.getHandler() : null);
// 调用异常处理器处理异常
mv = processHandlerException(request, response, handler, exception);
errorView = (mv != null);
}
}
// Did the handler return a view to render?
// 渲染页面
if (mv != null && !mv.wasCleared()) {
render(mv, request, response);
if (errorView) {
WebUtils.clearErrorRequestAttributes(request);
}
}
else {
}
if (WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {
// Concurrent handling started during a forward
return;
}
// 触发Interceptor.afterCompletion
if (mappedHandler != null) {
mappedHandler.triggerAfterCompletion(request, response, null);
}
}
异常解析processHandlerException
protected ModelAndView processHandlerException(HttpServletRequest request, HttpServletResponse response,
Object handler, Exception ex) throws Exception {
// Check registered HandlerExceptionResolvers...
ModelAndView exMv = null;
// 使用异常处理器来进行处理
for (HandlerExceptionResolver handlerExceptionResolver : this.handlerExceptionResolvers) {
exMv = handlerExceptionResolver.resolveException(request, response, handler, ex);
if (exMv != null) {
break;
}
}
if (exMv != null) {
if (exMv.isEmpty()) {
request.setAttribute(EXCEPTION_ATTRIBUTE, ex);
return null;
}
// We might still need view name translation for a plain error model...
if (!exMv.hasView()) {
exMv.setViewName(getDefaultViewName(request));
}
if (logger.isDebugEnabled()) {
logger.debug("Handler execution resulted in exception - forwarding to resolved error view: " + exMv, ex);
}
WebUtils.exposeErrorRequestAttributes(request, ex, getServletName());
return exMv;
}
throw ex;
}
https://zhhll.icu/2021/框架/springmvc/底层剖析/1.DispatcherServlet/
原文始发于微信公众号（bug生产基地）：一文带你搞懂DispatcherServlet前端控制器
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