Springboot请求映射原理

springboot中的spring-boot-starter-web还是使用的spring-mvc。而spring-mvc中处理所有的请求的入口就是DispatcherServlet.

而DispatcherServlet就一定要重写doGet或者doPost，但是在springboot中的DispatcherServlet中没有这两个方法。

 

 

 而是在DispatcherServlet的父类FrameworkServlet中找到了。

 

 

 

@Override
protected final void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
	processRequest(request, response);
}


@Override
protected final void doPost(HttpServletRequest request, HttpServletResponse response)
		throws ServletException, IOException {
	processRequest(request, response);
}

　　看出不管是doGet还是doPost都是执行的processRequest这个方法。

processRequest方法

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 {
            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);
        }
    }

主要看第19行的doService(request, response);方法，而这个方法中又调用了核心的doDispatch方法，如下：

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 = getHandler(processedRequest);

　　通过getHandler方法拿到对应可以处理当前请求的mappedHandler;

protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
		if (this.handlerMappings != null) {
			for (HandlerMapping mapping : this.handlerMappings) {
				HandlerExecutionChain handler = mapping.getHandler(request);
				if (handler != null) {
					return handler;
				}
			}
		}
		return null;
	}

　　debug之后发现会有如下几个HandlerMapping;

 

 而我们需要找到的是

RequestMappingHandlerMapping：保存了所有@RequestMapping 和handler的映射规则。

 

 当有请求进来时，会循环尝试所有的HandlerMapping看是否有请求信息。

• 如果有就找到这个请求对应的handler
• 如果没有就是下一个 HandlerMapping

Springboot请求映射原理就是其实就是查询对应HandlerMapping进行请求处理