SpringMVC02DispatchServlet的执行过程5HandlerAdapter.handle()

Z时代
2024-01-10
分类：综合

HandlerAdapter.handle()此方法内有对请求参数的解析、调用Controller里的具体方法和对响应结果的处理。最终返回ModelAndView对象。

下面将介绍最核心的处理请求的HandlerAdapter.handle()方法，此方法通过调用对应的处理器对请求做出处理，并返回一个ModelAndView对象。HandlerAdapter是一个接口，因此handle()方法需要其子类实现。HandlerAdapter的类图如图所示。

重点分析的AbstractHandlerMethodAdapter类结构图如下：

挑选其中的AbstractHandlerMethodAdapter分析，handle()方法的实现如下：

/**
 * This implementation expects the handler to be an {@link HandlerMethod}.
 */
@Override
@Nullable
public final ModelAndView handle(HttpServletRequest request, 
    HttpServletResponse response, Object handler) throws Exception {
    return handleInternal(request, response, (HandlerMethod) handler);}

AbstractHandlerMethodAdapter中的handle()方法是调用RequestMappingHandlerAdapter类中的handleInternal()方法完成功能的。入参中的handler其实就是Controller中自定义的方法。RequestMappingHandlerAdapter类中handleInternal()方法实现如下：

@Override
protected ModelAndView handleInternal(HttpServletRequest request,
        HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {
    ModelAndView mav;
    checkRequest(request);
    // Execute invokeHandlerMethod in synchronized block if required.
    if (this.synchronizeOnSession) {
        HttpSession session = request.getSession(false);
        if (session != null) {
            Object mutex = WebUtils.getSessionMutex(session);
            synchronized (mutex) {
                mav = invokeHandlerMethod(request, response, handlerMethod);
            }
        }
        else {
            // No HttpSession available -> no mutex necessary
            mav = invokeHandlerMethod(request, response, handlerMethod);
        }
    }
    else {
        // No synchronization on session demanded at all...
        mav = invokeHandlerMethod(request, response, handlerMethod);
    }
    if (!response.containsHeader(HEADER_CACHE_CONTROL)) {
        if (getSessionAttributesHandler(handlerMethod).hasSessionAttributes()) {
            applyCacheSeconds(response, this.cacheSecondsForSessionAttributeHandlers);
        }
        else {
            prepareResponse(response);
        }
    }
    return mav;
}

从invokeHandlerMethod()方法的代码可以看到，其会调用invokeHandlerMethod()方法并返回一个ModelAndView对象。

invokeHandlerMethod()方法部分实现如下：

/**
 * Invoke the {@link RequestMapping} handler method preparing a {@link ModelAndView}
 * if view resolution is required.
 * @since 4.2
 * @see #createInvocableHandlerMethod(HandlerMethod)
 */
@Nullable
protected ModelAndView invokeHandlerMethod(HttpServletRequest request,
        HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {
    ServletWebRequest webRequest = new ServletWebRequest(request, response);
    try {
        WebDataBinderFactory binderFactory = getDataBinderFactory(handlerMethod);
        ModelFactory modelFactory = getModelFactory(handlerMethod, binderFactory);
        ServletInvocableHandlerMethod invocableMethod = createInvocableHandlerMethod(handlerMethod);
        // 设置解析方法参数的解析器
        if (this.argumentResolvers != null) {
            invocableMethod.setHandlerMethodArgumentResolvers(this.argumentResolvers);
        }
        // 设置处理执行结果的处理器
        if (this.returnValueHandlers != null) {
            invocableMethod.setHandlerMethodReturnValueHandlers(this.returnValueHandlers);
        }
        invocableMethod.setDataBinderFactory(binderFactory);
        invocableMethod.setParameterNameDiscoverer(this.parameterNameDiscoverer);
        ModelAndViewContainer mavContainer = new ModelAndViewContainer();
        mavContainer.addAllAttributes(RequestContextUtils.getInputFlashMap(request));
        modelFactory.initModel(webRequest, mavContainer, invocableMethod);
        mavContainer.setIgnoreDefaultModelOnRedirect(this.ignoreDefaultModelOnRedirect);
        AsyncWebRequest asyncWebRequest = WebAsyncUtils.createAsyncWebRequest(request, response);
        asyncWebRequest.setTimeout(this.asyncRequestTimeout);
        WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
        asyncManager.setTaskExecutor(this.taskExecutor);
        asyncManager.setAsyncWebRequest(asyncWebRequest);
        asyncManager.registerCallableInterceptors(this.callableInterceptors);
        asyncManager.registerDeferredResultInterceptors(this.deferredResultInterceptors);
        if (asyncManager.hasConcurrentResult()) {
            Object result = asyncManager.getConcurrentResult();
            mavContainer = (ModelAndViewContainer) asyncManager.getConcurrentResultContext()[0];
            asyncManager.clearConcurrentResult();
            LogFormatUtils.traceDebug(logger, traceOn -> {
                String formatted = LogFormatUtils.formatValue(result, !traceOn);
                return "Resume with async result [" + formatted + "]";
            });
            invocableMethod = invocableMethod.wrapConcurrentResult(result);
        }
        // 下面将分析这个方法
        invocableMethod.invokeAndHandle(webRequest, mavContainer);
        if (asyncManager.isConcurrentHandlingStarted()) {
            return null;
        }
        return getModelAndView(mavContainer, modelFactory, webRequest);
    }
    finally {
        webRequest.requestCompleted();
    }}

invokeHandlerMethod()方法主要将请求参数和处理方法进行封装，并通过封装后的方法对象ServletInvocableHandlerMethod进行方法调用：

/**
 * Invoke the method and handle the return value through one of the
 * configured {@link HandlerMethodReturnValueHandler HandlerMethodReturnValueHandlers}.
 * @param webRequest the current request
 * @param mavContainer the ModelAndViewContainer for this request
 * @param providedArgs "given" arguments matched by type (not resolved)
 */
public void invokeAndHandle(ServletWebRequest webRequest, ModelAndViewContainer mavContainer,
        Object... providedArgs) throws Exception {
    // 分析这个方法
    Object returnValue = invokeForRequest(webRequest, mavContainer, providedArgs);
    setResponseStatus(webRequest);
    if (returnValue == null) {
        if (isRequestNotModified(webRequest) || getResponseStatus() != null || mavContainer.isRequestHandled()) {
            mavContainer.setRequestHandled(true);
            return;
        }
    }
    else if (StringUtils.hasText(getResponseStatusReason())) {
        mavContainer.setRequestHandled(true);
        return;
    }
    mavContainer.setRequestHandled(false);
    Assert.state(this.returnValueHandlers != null, "No return value handlers");
    try {
        // 将返回值通过这个方法封装到ModelAndViewContainer对象中
        this.returnValueHandlers.handleReturnValue(
                returnValue, getReturnValueType(returnValue), mavContainer, webRequest);
    }
    catch (Exception ex) {
        if (logger.isTraceEnabled()) {
            logger.trace(formatErrorForReturnValue(returnValue), ex);
        }
        throw ex;
    }}

这里要注意，invokeAndHandle()方法调用了invokeForRequest()方法，invokeForRequest()方法实现如下：(这个方法在InvocableHandlerMethod类中)

/**
 * Invoke the method after resolving its argument values in the context of the given request.
 * <p>Argument values are commonly resolved through
 * {@link HandlerMethodArgumentResolver HandlerMethodArgumentResolvers}.
 * The {@code providedArgs} parameter however may supply argument values to be used directly,
 * i.e. without argument resolution. Examples of provided argument values include a
 * {@link WebDataBinder}, a {@link SessionStatus}, or a thrown exception instance.
 * Provided argument values are checked before argument resolvers.
 * <p>Delegates to {@link #getMethodArgumentValues} and calls {@link #doInvoke} with the
 * resolved arguments.
 * @param request the current request
 * @param mavContainer the ModelAndViewContainer for this request
 * @param providedArgs "given" arguments matched by type, not resolved
 * @return the raw value returned by the invoked method
 * @throws Exception raised if no suitable argument resolver can be found,
 * or if the method raised an exception
 * @see #getMethodArgumentValues
 * @see #doInvoke
 */
@Nullable
public Object invokeForRequest(NativeWebRequest request, @Nullable ModelAndViewContainer mavContainer,
        Object... providedArgs) throws Exception {
    Object[] args = getMethodArgumentValues(request, mavContainer, providedArgs);
    if (logger.isTraceEnabled()) {
        logger.trace("Arguments: " + Arrays.toString(args));
    }
    return doInvoke(args);}

从方法实现可以看出，invokeForRequest()方法会首先获取请求中的处理方法执行所需要的参数，然后调用doInvoke()方法如下

/**
 * Invoke the handler method with the given argument values.
 */
@Nullable
protected Object doInvoke(Object... args) throws Exception {
    ReflectionUtils.makeAccessible(getBridgedMethod());
    try {
        return getBridgedMethod().invoke(getBean(), args);
    }
    catch (IllegalArgumentException ex) {
        assertTargetBean(getBridgedMethod(), getBean(), args);
        String text = (ex.getMessage() != null ? ex.getMessage() : "Illegal argument");
        throw new IllegalStateException(formatInvokeError(text, args), ex);
    }
    catch (InvocationTargetException ex) {
        // Unwrap for HandlerExceptionResolvers ...
        Throwable targetException = ex.getTargetException();
        if (targetException instanceof RuntimeException) {
            throw (RuntimeException) targetException;
        }
        else if (targetException instanceof Error) {
            throw (Error) targetException;
        }
        else if (targetException instanceof Exception) {
            throw (Exception) targetException;
        }
        else {
            throw new IllegalStateException(formatInvokeError("Invocation failure", args), targetException);
        }
    }}

doInvoke方法会调用getBridgedMethod()方法获取到Controller中开发者自定义的处理方法，并获得方法的Method对象，然后通过反射调用Method.invoke()方法完成对Controller中自定义的调用。

回到ServletInvocableHandlerMethod类的invokeAndHandle()方法，调用自定义方法后，将返回值通过handleReturnValue()方法封装到ModelAndViewContainer对象中。

再回到RequestMappingHandlerAdapter类的invokeHandlerMethod()方法中，执行完invokeAndHandle()方法后，将会调用getModelAndView()方法并返回ModelAndView对象。getModelAndView()方法如下：

@Nullable
private ModelAndView getModelAndView(ModelAndViewContainer mavContainer,
        ModelFactory modelFactory, NativeWebRequest webRequest) throws Exception {
    modelFactory.updateModel(webRequest, mavContainer);
    if (mavContainer.isRequestHandled()) {
        return null;
    }
    ModelMap model = mavContainer.getModel();
    ModelAndView mav = new ModelAndView(mavContainer.getViewName(), model, mavContainer.getStatus());
    if (!mavContainer.isViewReference()) {
        mav.setView((View) mavContainer.getView());
    }
    if (model instanceof RedirectAttributes) {
        Map<String, ?> flashAttributes = ((RedirectAttributes) model).getFlashAttributes();
        HttpServletRequest request = webRequest.getNativeRequest(HttpServletRequest.class);
        if (request != null) {
            RequestContextUtils.getOutputFlashMap(request).putAll(flashAttributes);
        }
    }
    return mav;}