SpringMVC运行原理

  • 2019 年 10 月 3 日
  • 筆記

 

 

 


按照上边的执行流程图,我们可以看出一个SpringMVC整体的一个执行轮廓,下面我们具体来分析下

 

首先服务器接收到一个请求,匹配并调用了我们的前端控制器(DispatcherServlet)也叫中央处理器的请求路径,在web.xml文件中配置,我们来看下配置文件

<servlet>          <servlet-name>springmvc</servlet-name>          <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>          <init-param>              <param-name>contextConfigLocation</param-name>              <param-value>classpath:springmvc.xml</param-value>          </init-param>          <load-on-startup>1</load-on-startup>  </servlet>  <servlet-mapping>      <servlet-name>springmvc</servlet-name>
  <!-- / 代表匹配所有除了jsp文件的请求 --> <url-pattern>/</url-pattern> </servlet-mapping>

因为DispatcherServlet实际上是间接的继承了我们的HttpServlet,所以它就相当于一个Servlet,SpringMVC帮我们封装好的一个Servlet,下面是继承体系

 

 

 所以说,当来了一个请求后,WEB容器将把请求交给我们的DispatcherServlet进行处理

DispatcherServlet接收到请求后,会把我们的请求信息交给HandlerMapping处理器映射器进行处理

HandlerMapping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,下面来看下底层执行代码

 protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {          Iterator var2 = this.handlerMappings.iterator();            HandlerExecutionChain handler;          do {              if (!var2.hasNext()) {                  return null;              }                HandlerMapping hm = (HandlerMapping)var2.next();              if (this.logger.isTraceEnabled()) {                  this.logger.trace("Testing handler map [" + hm + "] in DispatcherServlet with name '" + this.getServletName() + "'");              }                handler = hm.getHandler(request);//根据request对象获取handler,获取到的话将返回一个对象,没有的话将返回null  有兴趣童鞋自行深入查看          } while(handler == null);//如果handler为null继续执行循环            return handler;      }

如果没有找到的话将执行以下代码

 protected void noHandlerFound(HttpServletRequest request, HttpServletResponse response) throws Exception {          if (pageNotFoundLogger.isWarnEnabled()) {              pageNotFoundLogger.warn("No mapping found for HTTP request with URI [" + getRequestUri(request) + "] in DispatcherServlet with name '" + this.getServletName() + "'");          }            if (this.throwExceptionIfNoHandlerFound) {              ServletServerHttpRequest sshr = new ServletServerHttpRequest(request);              throw new NoHandlerFoundException(sshr.getMethod().name(), sshr.getServletRequest().getRequestURI(), sshr.getHeaders());          } else {              response.sendError(404);//响应404          }      }

找到成功的情况下,DispatcherServlet再次请求 处理器适配器(HandlerAdapter)调用相应的Handler 进行处理返回 ModelAndView 给 DispatcherServlet,底层代码,粗略看下即可,不是重点

 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 = this.checkMultipart(request);                  multipartRequestParsed = processedRequest != request;                  mappedHandler = this.getHandler(processedRequest);                  if (mappedHandler == null || mappedHandler.getHandler() == null) {                      this.noHandlerFound(processedRequest, response);                      return;                  }                    HandlerAdapter ha = this.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 (this.logger.isDebugEnabled()) {                          this.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;                  }                    mv = ha.handle(processedRequest, response, mappedHandler.getHandler()); //在这里边调用相应的Handler,并通过这个方法返回ModelAndModel给DispatcherServlet                  if (asyncManager.isConcurrentHandlingStarted()) {                      return;                  }                    this.applyDefaultViewName(request, mv);                  mappedHandler.applyPostHandle(processedRequest, response, mv);              } catch (Exception var19) {                  dispatchException = var19;              }                this.processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);          } catch (Exception var20) {              this.triggerAfterCompletion(processedRequest, response, mappedHandler, var20);          } catch (Error var21) {              this.triggerAfterCompletionWithError(processedRequest, response, mappedHandler, var21);          } finally {              if (asyncManager.isConcurrentHandlingStarted()) {                  if (mappedHandler != null) {                      mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);                  }              } else if (multipartRequestParsed) {                  this.cleanupMultipart(processedRequest);              }            }        }

然后DispatcherServlet将ModelAndView请求对应的ViewResolver(视图解析器)解析视图,然后返回具体的View,底层实现

 protected View resolveViewName(String viewName, Map<String, Object> model, Locale locale, HttpServletRequest request) throws Exception {          Iterator var5 = this.viewResolvers.iterator();            View view;          do {              if (!var5.hasNext()) {                  return null;              }                ViewResolver viewResolver = (ViewResolver)var5.next();              view = viewResolver.resolveViewName(viewName, locale);          } while(view == null);            return view;      }

DispatcherServlet对View视图进行渲染,也就是把模型数据填充到视图里边,底层执行代码

protected void render(ModelAndView mv, HttpServletRequest request, HttpServletResponse response) throws Exception {          Locale locale = this.localeResolver.resolveLocale(request);          response.setLocale(locale);          View view;          if (mv.isReference()) {              view = this.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 '" + this.getServletName() + "'");              }          } else {              view = mv.getView();              if (view == null) {                  throw new ServletException("ModelAndView [" + mv + "] neither contains a view name nor a " + "View object in servlet with name '" + this.getServletName() + "'");              }          }            if (this.logger.isDebugEnabled()) {              this.logger.debug("Rendering view [" + view + "] in DispatcherServlet with name '" + this.getServletName() + "'");          }            try {              view.render(mv.getModelInternal(), request, response);          } catch (Exception var7) {              if (this.logger.isDebugEnabled()) {                  this.logger.debug("Error rendering view [" + view + "] in DispatcherServlet with name '" + this.getServletName() + "'", var7);              }                throw var7;          }      }

最后DispatcherServlet将视图传递给前台

 

PS:

Spring MVC核心组件:
    1.DispatcherServlet(中央处理器):将请求转发给控制器

    2.Controller(控制器):处理请求的控制器

    3.HandlerMapping(映射处理器):负责映射中央处理器转发给Controller时的映射策略

    4.ModelAndView:服务器返回数据以及视图层的封装类

    5.ViewResolver(视图解析器):解析具体的视图

 

当用户发起请求后,执行DiapacherServlet,如果是JSP直接调用jsp页面.如果不是JSP,DiapacherServlet调用HandlerMapping判断请求URL是否合法,如果URL不存在报错,如果URL存在使用HandlerAdapter调用具体的HandlerMethod,当Handler执行完成后会返回ModelAndView,会被ViewResovler解析,调用具体的物理视图.
最终响应给客户端浏览器.