SpringMVC运行原理
2019-09-17 10:41:44来源:博客园 阅读 ()
SpringMVC运行原理
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.
原文链接:https://www.cnblogs.com/arebirth/p/springmvcexecutereal.html
如有疑问请与原作者联系
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