【JavaEE进阶】 拦截器(DispatcherServlet)源码简介

@Override
public final void init() throws ServletException {
    try {
        // ServletConfigPropertyValues 是静态内部类，使⽤ ServletConfig 获取
        web.xml 中配置的参数
        PropertyValues pvs = new
                ServletConfigPropertyValues(getServletConfig(), this.requiredProperties);
        // 使⽤ BeanWrapper 来构造 DispatcherServlet
        BeanWrapper bw = PropertyAccessorFactory.forBeanPropertyAccess(this);
        ResourceLoader resourceLoader = new
                ServletContextResourceLoader(getServletContext());
        bw.registerCustomEditor(Resource.class, new
                ResourceEditor(resourceLoader, getEnvironment()));
        initBeanWrapper(bw);
        bw.setPropertyValues(pvs, true);
    } catch (BeansException ex) {}
        // 让⼦类实现的⽅法，这种在⽗类定义在⼦类实现的⽅式叫做模版⽅法模式
    initServletBean();
}

/**
 * Overridden method of {@link HttpServletBean}, invoked after any bean
 properties
 * have been set. Creates this servlet's WebApplicationContext.
 */
@Override
protected final void initServletBean() throws ServletException {
    getServletContext().log("Initializing Spring " + getClass().getSimpleName()
            + " '" + getServletName() + "'");
    if (logger.isInfoEnabled()) {
        logger.info("Initializing Servlet '" + getServletName() + "'");
    }
    long startTime = System.currentTimeMillis();
    try {
//创建ApplicationContext容器
        this.webApplicationContext = initWebApplicationContext();
        initFrameworkServlet();
    }
    catch (ServletException | RuntimeException ex) {
        logger.error("Context initialization failed", ex);
        throw ex;
    }
    if (logger.isDebugEnabled()) {
        String value = this.enableLoggingRequestDetails ?
                "shown which may lead to unsafe logging of potentially sensitive
        data" :
        "masked to prevent unsafe logging of potentially sensitive data";
        logger.debug("enableLoggingRequestDetails='" +
                this.enableLoggingRequestDetails +
                "': request parameters and headers will be " + value);
    }
    if (logger.isInfoEnabled()) {
        logger.info("Completed initialization in " + (System.currentTimeMillis()
                - startTime) + " ms");
    }
}

protected WebApplicationContext initWebApplicationContext() {
//...
    if (!this.refreshEventReceived) {
//初始化Spring MVC
        synchronized (this.onRefreshMonitor) {
            onRefresh(wac);
        }
    }
    return wac;
}

@Override
protected void onRefresh(ApplicationContext context) {
    initStrategies(context);
}
/**
 * Initialize the strategy objects that this servlet uses.
 * <p>May be overridden in subclasses in order to initialize further strategy
 objects.
 */
protected void initStrategies(ApplicationContext context) {
    initMultipartResolver(context);
    initLocaleResolver(context);
    initThemeResolver(context);
    initHandlerMappings(context);
    initHandlerAdapters(context);
    initHandlerExceptionResolvers(context);
    initRequestToViewNameTranslator(context);
    initViewResolvers(context);
    initFlashMapManager(context);
}

protected void doDispatch(HttpServletRequest request, HttpServletResponse
        response) throws Exception {
    HttpServletRequest processedRequest = request;
    HandlerExecutionChain mappedHandler = null;
    boolean multipartRequestParsed = false;
    WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
    try {
        try {
            ModelAndView mv = null;
            Exception dispatchException = null;
            try {
                processedRequest = this.checkMultipart(request);
                multipartRequestParsed = processedRequest != request;
//1. 获取执⾏链
//遍历所有的 HandlerMapping 找到与请求对应的Handler
                mappedHandler = this.getHandler(processedRequest);
                if (mappedHandler == null) {
                    this.noHandlerFound(processedRequest, response);
                    return;
                }
//2. 获取适配器
//遍历所有的 HandlerAdapter，找到可以处理该 Handler 的
                HandlerAdapter
                HandlerAdapter ha =
                        this.getHandlerAdapter(mappedHandler.getHandler());
                String method = request.getMethod();
                boolean isGet = HttpMethod.GET.matches(method);
                if (isGet || HttpMethod.HEAD.matches(method)) {
                    long lastModified = ha.getLastModified(request,
                            mappedHandler.getHandler());
                    if ((new ServletWebRequest(request,
                            response)).checkNotModified(lastModified) && isGet) {
                        return;
                    }
                }
//3. 执⾏拦截器preHandle⽅法
                if (!mappedHandler.applyPreHandle(processedRequest, response))
                {
                    return;
                }
//4. 执⾏⽬标⽅法
                mv = ha.handle(processedRequest, response,
                        mappedHandler.getHandler());
                if (asyncManager.isConcurrentHandlingStarted()) {
                    return;
                }
                this.applyDefaultViewName(processedRequest, mv);
//5. 执⾏拦截器postHandle⽅法
                mappedHandler.applyPostHandle(processedRequest, response, mv);
            } catch (Exception var20) {
                dispatchException = var20;
            } catch (Throwable var21) {
                dispatchException = new NestedServletException("Handler
                        dispatch failed", var21);
            }
//6. 处理视图, 处理之后执⾏拦截器afterCompletion⽅法
            this.processDispatchResult(processedRequest, response,
                    mappedHandler, mv, (Exception)dispatchException);
        } catch (Exception var22) {
//7. 执⾏拦截器afterCompletion⽅法
            this.triggerAfterCompletion(processedRequest, response,
                    mappedHandler, var22);
        } catch (Throwable var23) {
            this.triggerAfterCompletion(processedRequest, response,
                    mappedHandler, new NestedServletException("Handler processing failed", var23));
        }
    } finally {
        if (asyncManager.isConcurrentHandlingStarted()) {
            if (mappedHandler != null) {
                mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
            }
        } else if (multipartRequestParsed) {
            this.cleanupMultipart(processedRequest);
        }
    }
}

boolean applyPreHandle(HttpServletRequest request, HttpServletResponse
        response) throws Exception {
    for(int i = 0; i < this.interceptorList.size(); this.interceptorIndex =
            i++) {
        // 获取项⽬中使⽤的拦截器 HandlerInterceptor
        HandlerInterceptor interceptor =
                (HandlerInterceptor)this.interceptorList.get(i);
        if (!interceptor.preHandle(request, response, this.handler)) {
            this.triggerAfterCompletion(request, response, (Exception)null);
            return false;
        }
    }
    return true;
}