SpringMVC中从doDispatch如何一步步调用到controller的方法

以一个简单请求为例进行说明：

@RestController
public class DemoController {

    @GetMapping("hello")
    public String sayHello() {
        return "hello world";
    }
}

首先列一下doDispatch方法进行说明：

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.根据请求的url获取处理请求的controller和controller中的方法。
                mappedHandler = getHandler(processedRequest);
                if (mappedHandler == null) {
                    noHandlerFound(processedRequest, response);
                    return;
                }

                // Determine handler adapter for the current request.根据处理器的类型获取处理器的适配器，使用适配器通过反射进行真正的方法调用。
                HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());

                // Process last-modified header, if supported by the handler.
                String method = request.getMethod();
                boolean isGet = "GET".equals(method);
                if (isGet || "HEAD".equals(method)) {
                    long lastModified = ha.getLastModified(request, mappedHandler.getHandler());
                    if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
                        return;
                    }
                }

                if (!mappedHandler.applyPreHandle(processedRequest, response)) {
                    return;
                }

                // Actually invoke the handler.适配器处理请求（通过反射调用controller中的方法）。
                mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

                if (asyncManager.isConcurrentHandlingStarted()) {
                    return;
                }

                applyDefaultViewName(processedRequest, mv);
                mappedHandler.applyPostHandle(processedRequest, response, mv);
            }
            catch (Exception ex) {
                dispatchException = ex;
            }
            catch (Throwable err) {
                // As of 4.3, we're processing Errors thrown from handler methods as well,
                // making them available for @ExceptionHandler methods and other scenarios.
                dispatchException = new NestedServletException("Handler dispatch failed", err);
            }
            processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
        }
        catch (Exception ex) {
            triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
        }
        catch (Throwable err) {
            triggerAfterCompletion(processedRequest, response, mappedHandler,
                    new NestedServletException("Handler processing failed", err));
        }
        finally {
            if (asyncManager.isConcurrentHandlingStarted()) {
                // Instead of postHandle and afterCompletion
                if (mappedHandler != null) {
                    mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
                }
            }
            else {
                // Clean up any resources used by a multipart request.
                if (multipartRequestParsed) {
                    cleanupMultipart(processedRequest);
                }
            }
        }
    }

下面打断点一步步跟一下：

1-获取mappedHandler = getHandler(processedRequest); 获取处理请求的controller信息和方法信息。

2-HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());根据处理器获取适配器，从断点看适配器类型为：RequestMappingHandlerAdapter。

3-mv = ha.handle(processedRequest, response, mappedHandler.getHandler()); 真正调用处理方法。

AbstractHandlerMethodAdapter.class(RequestMappingHandlerAdapter的父类)

    @Override
　　@Nullable

public final ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)
            throws Exception {
        return handleInternal(request, response, (HandlerMethod) handler);
    }

RequestMappingHandlerAdapter.class

@Override
    protected ModelAndView handleInternal(HttpServletRequest request,
            HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {

        ModelAndView mav;
　　　　　　......
       // No synchronization on session demanded at all... 调用此方法继续执行
            mav = invokeHandlerMethod(request, response, handlerMethod);
　　　　　　......
        return mav;
    }

@Nullable
    protected ModelAndView invokeHandlerMethod(HttpServletRequest request,
            HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {
　　　　　　......
　　　　　　　　//调用此方法继续执行
            invocableMethod.invokeAndHandle(webRequest, mavContainer);
　　　　　　......
    }

public void invokeAndHandle(ServletWebRequest webRequest, ModelAndViewContainer mavContainer,
            Object... providedArgs) throws Exception {
　　　　　　//调用此方法继续执行
        Object returnValue = invokeForRequest(webRequest, mavContainer, providedArgs);
    }

InvocableHandlerMethod.class

  @Nullable
    public Object invokeForRequest(NativeWebRequest request, @Nullable ModelAndViewContainer mavContainer, Object... providedArgs) throws Exception {
        Object[] args = this.getMethodArgumentValues(request, mavContainer, providedArgs);
        if (this.logger.isTraceEnabled()) {
            this.logger.trace("Arguments: " + Arrays.toString(args));
        }
　　　　　　//调用此方法
        return this.doInvoke(args);
    }

@Nullable
    protected Object doInvoke(Object... args) throws Exception {
        ReflectionUtils.makeAccessible(this.getBridgedMethod());
　　　　　　......
　　　　　　　　//反射执行controller中的处理方法
            return this.getBridgedMethod().invoke(this.getBean(), args);
　　　　　　......

    }

调试获取this.getBridgedMethod()，Method为controller中的sayHello()处理方法:

调试获取this.getBean()为DemoCOntroller的一个对象：

即最后通过Method.class的public Object invoke(Object obj, Object... args)方法去完成DemoController中sayHello()方法的调用。