Spring MVC入门（十三）：DispatcherServlet服务过程

• 查看源码

# 查看Servlet接口中的service方法
public interface Servlet {
    void init(ServletConfig var1) throws ServletException;
 
    ServletConfig getServletConfig();
 
    void service(ServletRequest var1, ServletResponse var2) throws ServletException, IOException;
 
    String getServletInfo();
 
    void destroy();
}
 
# 查看GenericServlet中的service方法
public abstract void service(ServletRequest var1, ServletResponse var2) throws ServletException, IOException;
 
# 查看HttpServlet类中的service方法
    public void service(ServletRequest req, ServletResponse res) throws ServletException, IOException {
        if (req instanceof HttpServletRequest && res instanceof HttpServletResponse) {
            HttpServletRequest request = (HttpServletRequest)req;
            HttpServletResponse response = (HttpServletResponse)res;
            this.service(request, response);
        } else {
            throw new ServletException("non-HTTP request or response");
        }
    }
 
# 在HttpServlet类中的service方法中，将ServletRequest和ServletResponse 转为HttpServletRequest和HttpServletResponse 
 
# 之后调用this.service(request, response);方法
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        // 获取请求方式
        String method = req.getMethod();
        long lastModified;
        // 如果是get请求，调用this.doGet(req, resp);
        if (method.equals("GET")) {
            lastModified = this.getLastModified(req);
            if (lastModified == -1L) {
                this.doGet(req, resp);
            } else {
                long ifModifiedSince = req.getDateHeader("If-Modified-Since");
                if (ifModifiedSince < lastModified) {
                    this.maybeSetLastModified(resp, lastModified);
                    this.doGet(req, resp);
                } else {
                    resp.setStatus(304);
                }
            }
        } else if (method.equals("HEAD")) {
            lastModified = this.getLastModified(req);
            this.maybeSetLastModified(resp, lastModified);
            this.doHead(req, resp);
        // 如果是post请求，调用this.doPost(req, resp);
        } else if (method.equals("POST")) {
            this.doPost(req, resp);
        // 如果是put请求，调用this.doPut(req, resp);
        } else if (method.equals("PUT")) {
            this.doPut(req, resp);
        } else if (method.equals("DELETE")) {
            this.doDelete(req, resp);
        } else if (method.equals("OPTIONS")) {
            this.doOptions(req, resp);
        } else if (method.equals("TRACE")) {
            this.doTrace(req, resp);
        } else {
            String errMsg = lStrings.getString("http.method_not_implemented");
            Object[] errArgs = new Object[]{method};
            errMsg = MessageFormat.format(errMsg, errArgs);
            resp.sendError(501, errMsg);
        }
 
    }
 
# 查看HttpServletBean 类，没有service方法
 
# 查看FrameworkServlet 类，重写了HttpServlet 类中的service方法
	@Override
	protected void service(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
 
		HttpMethod httpMethod = HttpMethod.resolve(request.getMethod());
                // 如果请求方式为patch，则调用processRequest(request, response);
		if (httpMethod == HttpMethod.PATCH || httpMethod == null) {
			processRequest(request, response);
		}
		else {
                        // 如果请求方式不是patch，则调用父类的service方法
			super.service(request, response);
		}
	}
 
# 查看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);
		}
	}
 
# 执行了doService(request, response);
 
# 查看doService方法
	protected abstract void doService(HttpServletRequest request, HttpServletResponse response)
			throws Exception;
 
# 最后查看DispatcherServlet中的doService
	@Override
	protected void doService(HttpServletRequest request, HttpServletResponse response) throws Exception {
		logRequest(request);
 
		// Keep a snapshot of the request attributes in case of an include,
		// to be able to restore the original attributes after the include.
		Map<String, Object> attributesSnapshot = null;
		if (WebUtils.isIncludeRequest(request)) {
			attributesSnapshot = new HashMap<>();
			Enumeration<?> attrNames = request.getAttributeNames();
			while (attrNames.hasMoreElements()) {
				String attrName = (String) attrNames.nextElement();
				if (this.cleanupAfterInclude || attrName.startsWith(DEFAULT_STRATEGIES_PREFIX)) {
					attributesSnapshot.put(attrName, request.getAttribute(attrName));
				}
			}
		}
 
		// Make framework objects available to handlers and view objects.
		request.setAttribute(WEB_APPLICATION_CONTEXT_ATTRIBUTE, getWebApplicationContext());
		request.setAttribute(LOCALE_RESOLVER_ATTRIBUTE, this.localeResolver);
		request.setAttribute(THEME_RESOLVER_ATTRIBUTE, this.themeResolver);
		request.setAttribute(THEME_SOURCE_ATTRIBUTE, getThemeSource());
 
		if (this.flashMapManager != null) {
			FlashMap inputFlashMap = this.flashMapManager.retrieveAndUpdate(request, response);
			if (inputFlashMap != null) {
				request.setAttribute(INPUT_FLASH_MAP_ATTRIBUTE, Collections.unmodifiableMap(inputFlashMap));
			}
			request.setAttribute(OUTPUT_FLASH_MAP_ATTRIBUTE, new FlashMap());
			request.setAttribute(FLASH_MAP_MANAGER_ATTRIBUTE, this.flashMapManager);
		}
 
		RequestPath requestPath = null;
		if (this.parseRequestPath && !ServletRequestPathUtils.hasParsedRequestPath(request)) {
			requestPath = ServletRequestPathUtils.parseAndCache(request);
		}
 
		try {
			doDispatch(request, response);
		}
		finally {
			if (!WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {
				// Restore the original attribute snapshot, in case of an include.
				if (attributesSnapshot != null) {
					restoreAttributesAfterInclude(request, attributesSnapshot);
				}
			}
			if (requestPath != null) {
				ServletRequestPathUtils.clearParsedRequestPath(request);
			}
		}
	}
 
# 以上方法中执行了doDispatch(request, response);方法
 
# 查看doDispatch方法
	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);
				if (mappedHandler == null) {
					noHandlerFound(processedRequest, response);
					return;
				}
 
				// Determine handler adapter for the current request.
				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.
				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);
				}
			}
		}
	}
 
# 以上方法的核心为如下，在该方法中对请求进行统一处理
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());