SpringMVC的原理

朱雀 2022-11-26 02:57 153阅读 0赞

SpringMVC的MVC即模型-视图-控制器，该框架围绕一个DispatcherServlet设计，DispatcherServlet会把请求分发给各个处理器进行处理。SpringMVC的工作流程如下图所示。  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM2OTg2MDE1_size_16_color_FFFFFF_t_70]

1.  浏览器发起HTTP请求，发送给DS；
2.  DS寻找映射处理器HandlerMapping，这个对象是个Mapping对象，保存了URL->方法的映射关系，通过HandlerMapping找到对应的Controller；
3.  调用Controller；
4.  Controller调用Service；
5.  Controller返回ModelAndView，ModelAndView包含了数据Model和视图名称；
6.  通过试图处理器ViewResolver找到对应的视图View，并将数据Model交给视图View渲染；
7.  返回HTTP响应。

精简后的源码如下：

@Override
    	protected void doService(HttpServletRequest request, HttpServletResponse response) { 
    		doDispatch(request, response); // 在doservice方法中调用doDispath方法
    	}

protected void doDispatch(HttpServletRequest request, HttpServletResponse response) { 
    
    		// 根据当前请求在HandlerMapping中找到Controller，HandlerMapping是个接口，一般在其实现类RequestMappingHandlerMapping中调用方法，返回的controller被包装在HandlerExecutionChain类中，HandlerExecutionChain中主要包含Controller和Interceptor拦截器
    		HandlerExecutionChain mappedHandler = getHandler(processedRequest);
    		// 如果没找到，返回404
    		if (mappedHandler == null) { 
    			noHandlerFound(processedRequest, response);
    			return;
    		}
    		// 根据当前controller找到HandlerAdapter，一般是RequestMappingHandlerAdapter
    		HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());
    		// 执行前置拦截器
    		if (!mappedHandler.applyPreHandle(processedRequest, response)) { 
    			return;
    		}
    		// 调用handle方法返回ModelAndView 
    		ModelAndView  mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
    		// 调用后置拦截器
    		mappedHandler.applyPostHandle(processedRequest, response, mv);
    		processDispatchResult(processedRequest, response, mappedHandler, mv);
    		
    	}

private void processDispatchResult(HttpServletRequest request, HttpServletResponse response,
    			@Nullable HandlerExecutionChain mappedHandler, @Nullable ModelAndView mv,
    			@Nullable Exception exception) throws Exception { 
    		// 通过ViewResolver返回View
    		if (mv != null && !mv.wasCleared()) { 
    			render(mv, request, response);
    		}
    	}

protected void render(ModelAndView mv, HttpServletRequest request, HttpServletResponse response) throws Exception { 
    		// Determine locale for request and apply it to the response.
    		Locale locale =
    				(this.localeResolver != null ? this.localeResolver.resolveLocale(request) : request.getLocale());
    		response.setLocale(locale);
    
    		View view;
    		String viewName = mv.getViewName();
    		if (viewName != null) { 
    			// 通过viewName解析出View
    			view = resolveViewName(viewName, mv.getModelInternal(), locale, request);
    
    		}
    		// 视图渲染
    		view.render(mv.getModelInternal(), request, response);
    	}

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM2OTg2MDE1_size_16_color_FFFFFF_t_70]: /images/20221124/f9127498da3940daa9ea90d757bbe715.png