SpringMVC运行原理，MVC的基本原理
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
springmvc
org.springframework.web.servlet.DispatcherServlet
contextConfigLocation
classpath:springmvc.xml
1
springmvc
/
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) throwsException {
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DispatcherServletif(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 model, Locale locale, HttpServletRequest request) throwsException {
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);returnview;
}
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) throwsException {
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);
}throwvar7;
}
}
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.
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