SpringMVC--注解配置SpringMVC、SpringMVC执行流程

注解配置SpringMVC

使用配置类和注解代替web.xml和SpringMVC配置文件的功能

创建初始化类，代替web.xml

在Servlet3.0环境中，容器会在类路径中查找实现javax.servlet.ServletContainerInitializer接口的类， 如果找到的话就用它来配置Servlet容器。 Spring提供了这个接口的实现，名为 SpringServletContainerInitializer，这个类反过来又会查找实现WebApplicationInitializer的类并将配 置的任务交给它们来完成。Spring3.2引入了一个便利的WebApplicationInitializer基础实现，名为 AbstractAnnotationConfigDispatcherServletInitializer，当我们的类扩展了 AbstractAnnotationConfigDispatcherServletInitializer并将其部署到Servlet3.0容器的时候，容器会自 动发现它，并用它来配置Servlet上下文。

public class WebInit extends
AbstractAnnotationConfigDispatcherServletInitializer {
/**
* 指定spring的配置类 * @return
*/
@Overrideprotected Class<?>[] getRootConfigClasses() {return new Class[]{SpringConfig.class};
}
/**
* 指定SpringMVC的配置类 * @return
*/
@Overrideprotected Class<?>[] getServletConfigClasses() {return new Class[]{WebConfig.class};
}
/**
* 指定DispatcherServlet的映射规则，即url-pattern * @return
*/
@Overrideprotected String[] getServletMappings() {return new String[]{"/"};
}
/**
* 添加过滤器 * @return */
@Overrideprotected Filter[] getServletFilters() {CharacterEncodingFilter encodingFilter = new CharacterEncodingFilter();encodingFilter.setEncoding("UTF-8");encodingFilter.setForceRequestEncoding(true);HiddenHttpMethodFilter hiddenHttpMethodFilter = new
HiddenHttpMethodFilter();return new Filter[]{encodingFilter, hiddenHttpMethodFilter};
} }

创建SpringConfig配置类，代替spring的配置文件

@Configuration
public class SpringConfig { //ssm整合之后，spring的配置信息写在此类中
}

创建WebConfig配置类，代替SpringMVC的配置文件

@Configuration
//扫描组件 @ComponentScan("com.atguigu.mvc.controller") //开启MVC注解驱动
@EnableWebMvc
public class WebConfig implements WebMvcConfigurer {
//使用默认的servlet处理静态资源
@Override
public void configureDefaultServletHandling(DefaultServletHandlerConfigurer
configurer) {configurer.enable();
}
//配置文件上传解析器
@Bean
public CommonsMultipartResolver multipartResolver(){return new CommonsMultipartResolver();}
//配置拦截器
@Override
public void addInterceptors(InterceptorRegistry registry) {FirstInterceptor firstInterceptor = new FirstInterceptor();registry.addInterceptor(firstInterceptor).addPathPatterns("/**");}
//配置视图控制/*@Overridepublic void addViewControllers(ViewControllerRegistry registry) {registry.addViewController("/").setViewName("index");}*/
//配置异常映射 /*@Override public void
configureHandlerExceptionResolvers(List<HandlerExceptionResolver> resolvers) {SimpleMappingExceptionResolver exceptionResolver = new
SimpleMappingExceptionResolver();
Properties prop = new Properties(); prop.setProperty("java.lang.ArithmeticException", "error"); //设置异常映射
exceptionResolver.setExceptionMappings(prop); //设置共享异常信息的键 exceptionResolver.setExceptionAttribute("ex"); resolvers.add(exceptionResolver);
}*/
//配置生成模板解析器
@Bean
public ITemplateResolver templateResolver() {WebApplicationContext webApplicationContext =
ContextLoader.getCurrentWebApplicationContext();
// ServletContextTemplateResolver需要一个ServletContext作为构造参数，可通过 WebApplicationContext 的方法获得ServletContextTemplateResolver templateResolver = new
ServletContextTemplateResolver(webApplicationContext.getServletContext());templateResolver.setPrefix("/WEB-INF/templates/");templateResolver.setSuffix(".html");templateResolver.setCharacterEncoding("UTF-8");templateResolver.setTemplateMode(TemplateMode.HTML);return templateResolver;
}
//生成模板引擎并为模板引擎注入模板解析器
@Bean
public SpringTemplateEngine templateEngine(ITemplateResolver
templateResolver) {SpringTemplateEngine templateEngine = new SpringTemplateEngine();templateEngine.setTemplateResolver(templateResolver);return templateEngine;
}
//生成视图解析器并未解析器注入模板引擎
@Bean
public ViewResolver viewResolver(SpringTemplateEngine templateEngine) {ThymeleafViewResolver viewResolver = new ThymeleafViewResolver();viewResolver.setCharacterEncoding("UTF-8");viewResolver.setTemplateEngine(templateEngine);return viewResolver;
}
}

测试功能

@RequestMapping("/")
public String index(){return "index";
}

SpringMVC执行流程

SpringMVC常用组件

• DispatcherServlet:前端控制器，不需要工程师开发，由框架提供
  作用:统一处理请求和响应，整个流程控制的中心，由它调用其它组件处理用户的请求
• HandlerMapping:处理器映射器，不需要工程师开发，由框架提供
  作用:根据请求的url、method等信息查找Handler，即控制器方法
• Handler:处理器，需要工程师开发
  作用:在DispatcherServlet的控制下Handler对具体的用户请求进行处理
• HandlerAdapter:处理器适配器，不需要工程师开发，由框架提供
  作用:通过HandlerAdapter对处理器(控制器方法)进行执行
• ViewResolver:视图解析器，不需要工程师开发，由框架提供
  作用:进行视图解析，得到相应的视图，例如:ThymeleafView、InternalResourceView、 RedirectView
• View:视图
  作用:将模型数据通过页面展示给用户

DispatcherServlet初始化过程

DispatcherServlet 本质上是一个 Servlet，所以天然的遵循 Servlet 的生命周期。所以宏观上是 Servlet 生命周期来进行调度。

1. 初始化WebApplicationContext
   所在类:org.springframework.web.servlet.FrameworkServlet

   protected WebApplicationContext initWebApplicationContext() {WebApplicationContext rootContext = WebApplicationContextUtils.getWebApplicationContext(this.getServletContext());WebApplicationContext wac = null;if (this.webApplicationContext != null) {wac = this.webApplicationContext;if (wac instanceof ConfigurableWebApplicationContext) {ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext)wac;if (!cwac.isActive()) {if (cwac.getParent() == null) {cwac.setParent(rootContext);}this.configureAndRefreshWebApplicationContext(cwac);}}}if (wac == null) {wac = this.findWebApplicationContext();}if (wac == null) {wac = this.createWebApplicationContext(rootContext);}if (!this.refreshEventReceived) {synchronized(this.onRefreshMonitor) {this.onRefresh(wac);}}if (this.publishContext) {String attrName = this.getServletContextAttributeName();this.getServletContext().setAttribute(attrName, wac);}return wac;}

2. 创建WebApplicationContext
   所在类:org.springframework.web.servlet.FrameworkServlet

protected WebApplicationContext createWebApplicationContext(@Nullable
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");
}
// 通过反射创建 IOC 容器对象 ConfigurableWebApplicationContext wac =(ConfigurableWebApplicationContext)
BeanUtils.instantiateClass(contextClass);
wac.setEnvironment(getEnvironment());
// 设置父容器
wac.setParent(parent);
String configLocation = getContextConfigLocation(); if (configLocation != null) {wac.setConfigLocation(configLocation);}configureAndRefreshWebApplicationContext(wac);return wac;
}

3. DispatcherServlet初始化策略

FrameworkServlet创建WebApplicationContext后，刷新容器，调用onRefresh(wac)，此方法在 DispatcherServlet中进行了重写，调用了initStrategies(context)方法，初始化策略，即初始化 DispatcherServlet的各个组件

所在类:org.springframework.web.servlet.DispatcherServlet

protected void initStrategies(ApplicationContext context) {initMultipartResolver(context);initLocaleResolver(context);initThemeResolver(context);initHandlerMappings(context);initHandlerAdapters(context);initHandlerExceptionResolvers(context);initRequestToViewNameTranslator(context);initViewResolvers(context);initFlashMapManager(context);
}

DispatcherServlet调用组件处理请求

1. processRequest()

FrameworkServlet重写HttpServlet中的service()和doXxx()，这些方法中调用了 processRequest(request, response)

所在类:org.springframework.web.servlet.FrameworkServlet

protected final void processRequest(HttpServletRequest request,
HttpServletResponse response)throws ServletException, IOException {long startTime = System.currentTimeMillis();Throwable failureCause = null;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());initContextHolders(request, localeContext, requestAttributes);
try {
// 执行服务，doService()是一个抽象方法，在DispatcherServlet中进行了重写 doService(request, response);}catch (ServletException | IOException ex) {failureCause = ex;
throw ex; }catch (Throwable ex) {failureCause = ex;throw new NestedServletException("Request processing failed", ex);
}finally {resetContextHolders(request, previousLocaleContext, previousAttributes);if (requestAttributes != null) {requestAttributes.requestCompleted();}logResult(request, response, failureCause, asyncManager);publishRequestHandledEvent(request, response, startTime, failureCause);}
}

2. doService
   所在类:org.springframework.web.servlet.DispatcherServlet

@Override
protected void doService(HttpServletRequest request, HttpServletResponse
response) throws Exception {
logRequest(request);// 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;if (WebUtils.isIncludeRequest(request)) {attributesSnapshot = new HashMap<>();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());if (this.flashMapManager != null) {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);
}RequestPath requestPath = null;if (this.parseRequestPath &&
!ServletRequestPathUtils.hasParsedRequestPath(request)) {requestPath = ServletRequestPathUtils.parseAndCache(request);}
try {
// 处理请求和响应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);}}if (requestPath != null) {ServletRequestPathUtils.clearParsedRequestPath(request);}}}      

3. doDispatch()
   所在类:org.springframework.web.servlet.DispatcherServlet

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 {processedRequest = checkMultipart(request);multipartRequestParsed = (processedRequest != request);// Determine handler for the current request./*
mappedHandler:调用链 包含handler、interceptorList、interceptorIndex handler:浏览器发送的请求所匹配的控制器方法 interceptorList:处理控制器方法的所有拦截器集合 interceptorIndex:拦截器索引，控制拦截器afterCompletion()的执行
*/mappedHandler = getHandler(processedRequest);if (mappedHandler == null) {noHandlerFound(processedRequest, response);return; }
// Determine handler adapter for the current request.
// 通过控制器方法创建相应的处理器适配器，调用所对应的控制器方法 HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());// Process last-modified header, if supported by the handler.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;}
}
// 调用拦截器的preHandle()
if (!mappedHandler.applyPreHandle(processedRequest, response)) {
return;}// Actually invoke the handler.
// 由处理器适配器调用具体的控制器方法，最终获得ModelAndView对象mv = ha.handle(processedRequest, response,
mappedHandler.getHandler());if (asyncManager.isConcurrentHandlingStarted()) {return;
}
applyDefaultViewName(processedRequest, mv);
// 调用拦截器的postHandle()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);
}
// 后续处理:处理模型数据和渲染视图processDispatchResult(processedRequest, response, mappedHandler, mv,
dispatchException);}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 afterCompletionif (mappedHandler != null) {mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);}
} else {// Clean up any resources used by a multipart request.if (multipartRequestParsed) {cleanupMultipart(processedRequest);} }} 
}

4. processDispatchResult()

  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) {this.logger.debug("ModelAndViewDefiningException encountered", exception);mv = ((ModelAndViewDefiningException)exception).getModelAndView();} else {Object handler = mappedHandler != null ? mappedHandler.getHandler() : null;mv = this.processHandlerException(request, response, handler, exception);errorView = mv != null;}}// Did the handler return a view to render?if (mv != null && !mv.wasCleared()) {// 处理模型数据和渲染视图this.render(mv, request, response);if (errorView) {WebUtils.clearErrorRequestAttributes(request);}} else if (this.logger.isTraceEnabled()) {this.logger.trace("No view rendering, null ModelAndView returned.");}if (!WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {if (mappedHandler != null) {// Exception (if any) is already handled..// 调用拦截器的afterCompletion()mappedHandler.triggerAfterCompletion(request, response, (Exception)null);}}}

SpringMVC的执行流程

1. 用户向服务器发送请求，请求被SpringMVC 前端控制器 DispatcherServlet捕获。
2. DispatcherServlet对请求URL进行解析，得到请求资源标识符(URI)，判断请求URI对应的映射: a) 不存在
   i. 再判断是否配置了mvc:default-servlet-handler
   ii. 如果没配置，则控制台报映射查找不到，客户端展示404错误
   
   b) 存在,则执行下面的流程
3. 根据该URI，调用HandlerMapping获得该Handler配置的所有相关的对象(包括Handler对象以及
   Handler对象对应的拦截器)，最后以HandlerExecutionChain执行链对象的形式返回。
4. DispatcherServlet 根据获得的Handler，选择一个合适的HandlerAdapter。
5. 如果成功获得HandlerAdapter，此时将开始执行拦截器的preHandler(…)方法【正向】
6. 提取Request中的模型数据，填充Handler入参，开始执行Handler(Controller)方法，处理请求。 在填充Handler的入参过程中，根据你的配置，Spring将帮你做一些额外的工作:
   a) HttpMessageConveter: 将请求消息(如Json、xml等数据)转换成一个对象，将对象转换为指定 的响应信息
   b) 数据转换:对请求消息进行数据转换。如String转换成Integer、Double等
   c) 数据格式化:对请求消息进行数据格式化。 如将字符串转换成格式化数字或格式化日期等
   d) 数据验证: 验证数据的有效性(长度、格式等)，验证结果存储到BindingResult或Error中
7. Handler执行完成后，向DispatcherServlet 返回一个ModelAndView对象。
8. 此时将开始执行拦截器的postHandle(…)方法【逆向】。
9. 根据返回的ModelAndView(此时会判断是否存在异常:如果存在异常，则执行 HandlerExceptionResolver进行异常处理)选择一个适合的ViewResolver进行视图解析，根据Model 和View，来渲染视图。
10. 渲染视图完毕执行拦截器的afterCompletion(…)方法【逆向】。
11. 将渲染结果返回给客户端。