spring mvc 原理

1.RequestMappingHandlerMapping

1.继承了InitializingBean 加载所有的 Controller.class 和 RequestMapping.class

2. WebMvcAutoConfiguration 初始化时加载interception

3.根据url 获取在RequestMappingHandlerMapping获取handlerMethod，并包装成HandlerExecutionChain，并将RequestMappingHandlerMapping中的intercepters加入到 HandlerExecutionChain

加入规则如下

protected HandlerExecutionChain getHandlerExecutionChain(Object handler, HttpServletRequest request) {
        HandlerExecutionChain chain = (handler instanceof HandlerExecutionChain ?
                (HandlerExecutionChain) handler : new HandlerExecutionChain(handler));

        String lookupPath = this.urlPathHelper.getLookupPathForRequest(request);
        for (HandlerInterceptor interceptor : this.adaptedInterceptors) {
            if (interceptor instanceof MappedInterceptor) {
                MappedInterceptor mappedInterceptor = (MappedInterceptor) interceptor;
                if (mappedInterceptor.matches(lookupPath, this.pathMatcher)) {
                    chain.addInterceptor(mappedInterceptor.getInterceptor());
                }
            }
            else {
                chain.addInterceptor(interceptor);
            }
        }
        return chain;
    }

4.使用 handlerMethod 获取handlerAdapter

4.1 RequestMappingHandlerAdapter (初始化时，初始化adviceCache,和参数解析器)

@Override
    public void afterPropertiesSet() {
        // Do this first, it may add ResponseBody advice beans
        initControllerAdviceCache();

        if (this.argumentResolvers == null) {
            List<HandlerMethodArgumentResolver> resolvers = getDefaultArgumentResolvers();
            this.argumentResolvers = new HandlerMethodArgumentResolverComposite().addResolvers(resolvers);
        }
        if (this.initBinderArgumentResolvers == null) {
            List<HandlerMethodArgumentResolver> resolvers = getDefaultInitBinderArgumentResolvers();
            this.initBinderArgumentResolvers = new HandlerMethodArgumentResolverComposite().addResolvers(resolvers);
        }
        if (this.returnValueHandlers == null) {
            List<HandlerMethodReturnValueHandler> handlers = getDefaultReturnValueHandlers();
            this.returnValueHandlers = new HandlerMethodReturnValueHandlerComposite().addHandlers(handlers);
        }
    }

    private void initControllerAdviceCache() {
        if (getApplicationContext() == null) {
            return;
        }

        List<ControllerAdviceBean> adviceBeans = ControllerAdviceBean.findAnnotatedBeans(getApplicationContext());
        AnnotationAwareOrderComparator.sort(adviceBeans);

        List<Object> requestResponseBodyAdviceBeans = new ArrayList<>();

        for (ControllerAdviceBean adviceBean : adviceBeans) {
            Class<?> beanType = adviceBean.getBeanType();
            if (beanType == null) {
                throw new IllegalStateException("Unresolvable type for ControllerAdviceBean: " + adviceBean);
            }
            Set<Method> attrMethods = MethodIntrospector.selectMethods(beanType, MODEL_ATTRIBUTE_METHODS);
            if (!attrMethods.isEmpty()) {
                this.modelAttributeAdviceCache.put(adviceBean, attrMethods);
            }
            Set<Method> binderMethods = MethodIntrospector.selectMethods(beanType, INIT_BINDER_METHODS);
            if (!binderMethods.isEmpty()) {
                this.initBinderAdviceCache.put(adviceBean, binderMethods);
            }
            if (RequestBodyAdvice.class.isAssignableFrom(beanType) || ResponseBodyAdvice.class.isAssignableFrom(beanType)) {
                requestResponseBodyAdviceBeans.add(adviceBean);
            }
        }

        if (!requestResponseBodyAdviceBeans.isEmpty()) {
            this.requestResponseBodyAdvice.addAll(0, requestResponseBodyAdviceBeans);
        }

        if (logger.isDebugEnabled()) {
            int modelSize = this.modelAttributeAdviceCache.size();
            int binderSize = this.initBinderAdviceCache.size();
            int reqCount = getBodyAdviceCount(RequestBodyAdvice.class);
            int resCount = getBodyAdviceCount(ResponseBodyAdvice.class);
            if (modelSize == 0 && binderSize == 0 && reqCount == 0 && resCount == 0) {
                logger.debug("ControllerAdvice beans: none");
            }
            else {
                logger.debug("ControllerAdvice beans: " + modelSize + " @ModelAttribute, " + binderSize +
                        " @InitBinder, " + reqCount + " RequestBodyAdvice, " + resCount + " ResponseBodyAdvice");
            }
        }
    }

5.使用handlerAdapter handler方法获取ModerAndView

mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

在当前类和ControllerAdvice 中获取有InitBinder.class注解的方法全部封装在一起。（InitBinder用法https://blog.csdn.net/qq_38016931/article/details/82080940）

在当前类和ControllerAdvice 中获取有ModelAttribute且没有RequestMapping 的注解的方法，全部封装在一起。（ModelAttribute用法https://blog.csdn.net/abc997995674/article/details/80464023）

7.将注解有ModelAttribute的方法，初始化后绑定到sessionAttributes;

8. resolvers解析参数

例：RequestResponseBodyMethodProcessor

8.1 1.使用 binder和 messageConverters 转化 json或xml，或其他的为对象。

8.2 valid 校验参数

9.参数解析正常则调用代理对象

9.1使用代理对象的拦截器拦截方法，或初始化一些对象

9.2具体的方法调用

10.参数解析异常抛出异常

10.1

0 = {DefaultErrorAttributes@15395}
1 = {HandlerExceptionResolverComposite@12775}

10.2 HandlerExceptionResolverComposite里又含有三个异常

0 = {ExceptionHandlerExceptionResolver@15442} --使用 @ExceptionHandler 解决异常有些这里抛出的异常会导致发起/error

1 = {ResponseStatusExceptionResolver@15443} --解决@ResponseStatus或instanceof ResponseStatusException

2 = {DefaultHandlerExceptionResolver@12774} 针对于一些异常，重新发起（/error）请求

@Override
    @Nullable
    protected ModelAndView doResolveException(
            HttpServletRequest request, HttpServletResponse response, @Nullable Object handler, Exception ex) {

        try {
            if (ex instanceof HttpRequestMethodNotSupportedException) {
                return handleHttpRequestMethodNotSupported(
                        (HttpRequestMethodNotSupportedException) ex, request, response, handler);
            }
            else if (ex instanceof HttpMediaTypeNotSupportedException) {
                return handleHttpMediaTypeNotSupported(
                        (HttpMediaTypeNotSupportedException) ex, request, response, handler);
            }
            else if (ex instanceof HttpMediaTypeNotAcceptableException) {
                return handleHttpMediaTypeNotAcceptable(
                        (HttpMediaTypeNotAcceptableException) ex, request, response, handler);
            }
            else if (ex instanceof MissingPathVariableException) {
                return handleMissingPathVariable(
                        (MissingPathVariableException) ex, request, response, handler);
            }
            else if (ex instanceof MissingServletRequestParameterException) {
                return handleMissingServletRequestParameter(
                        (MissingServletRequestParameterException) ex, request, response, handler);
            }
            else if (ex instanceof ServletRequestBindingException) {
                return handleServletRequestBindingException(
                        (ServletRequestBindingException) ex, request, response, handler);
            }
            else if (ex instanceof ConversionNotSupportedException) {
                return handleConversionNotSupported(
                        (ConversionNotSupportedException) ex, request, response, handler);
            }
            else if (ex instanceof TypeMismatchException) {
                return handleTypeMismatch(
                        (TypeMismatchException) ex, request, response, handler);
            }
            else if (ex instanceof HttpMessageNotReadableException) {
                return handleHttpMessageNotReadable(
                        (HttpMessageNotReadableException) ex, request, response, handler);
            }
            else if (ex instanceof HttpMessageNotWritableException) {
                return handleHttpMessageNotWritable(
                        (HttpMessageNotWritableException) ex, request, response, handler);
            }
            else if (ex instanceof MethodArgumentNotValidException) {
                return handleMethodArgumentNotValidException(
                        (MethodArgumentNotValidException) ex, request, response, handler);
            }
            else if (ex instanceof MissingServletRequestPartException) {
                return handleMissingServletRequestPartException(
                        (MissingServletRequestPartException) ex, request, response, handler);
            }
            else if (ex instanceof BindException) {
                return handleBindException((BindException) ex, request, response, handler);
            }
            else if (ex instanceof NoHandlerFoundException) {
                return handleNoHandlerFoundException(
                        (NoHandlerFoundException) ex, request, response, handler);
            }
            else if (ex instanceof AsyncRequestTimeoutException) {
                return handleAsyncRequestTimeoutException(
                        (AsyncRequestTimeoutException) ex, request, response, handler);
            }
        }
        catch (Exception handlerEx) {
            if (logger.isWarnEnabled()) {
                logger.warn("Failure while trying to resolve exception [" + ex.getClass().getName() + "]", handlerEx);
            }
        }
        return null;
    }