spring系列MVC

 

1、初始化九大组件

protected void initStrategies(ApplicationContext context) {

		//TODO 初始化多组件上传
		initMultipartResolver(context);

		//TODO 初始化本地语言环境
		initLocaleResolver(context);

		//TODO 初始化模板处理器
		initThemeResolver(context);

		//TODO 初始化处理器映射器
		initHandlerMappings(context);

		//TODO 初始化处理器适配器（参数适配器）
		initHandlerAdapters(context);

		//TODO 初始化异常拦截器
		initHandlerExceptionResolvers(context);

		//TODO 初始化视图预处理器
		initRequestToViewNameTranslator(context);

		//TODO 初始化视图转换器
		initViewResolvers(context);

		//TODO 初始化FlashMap管理器：此管理器是用于在重定向的时候管理传递的参数的（重定向的时候参数隐秘传输，设置request的OUTPUT-FLASHMAP-...属性可以直接将值注入model）
		initFlashMapManager(context);
	}

2、建立URL和handle 的对应关系

建立URL和handle（controller中的method）是在AbstractDetectingUrlHandlerMapping类中的initApplicationContext方法

	@Override
	public void initApplicationContext() throws ApplicationContextException {
		super.initApplicationContext();
		detectHandlers();
	}


	protected void detectHandlers() throws BeansException {
		ApplicationContext applicationContext = obtainApplicationContext();
		if (logger.isDebugEnabled()) {
			logger.debug("Looking for URL mappings in application context: " + applicationContext);
		}
		String[] beanNames = (this.detectHandlersInAncestorContexts ?
				BeanFactoryUtils.beanNamesForTypeIncludingAncestors(applicationContext, Object.class) :
				applicationContext.getBeanNamesForType(Object.class));

		// Take any bean name that we can determine URLs for.
		for (String beanName : beanNames) {
			String[] urls = determineUrlsForHandler(beanName);
			if (!ObjectUtils.isEmpty(urls)) {
				// URL paths found: Let's consider it a handler.
				registerHandler(urls, beanName);
			}
			else {
				if (logger.isDebugEnabled()) {
					logger.debug("Rejected bean name '" + beanName + "': no URL paths identified");
				}
			}
		}
	}

最终会调用AbstractUrlHandlerMapping类中的registerHandler方法完成的，最终会把这个对应关系放在一个map里，map的key是handler的URL，map的value是URL对应的handle（controller）：

protected void registerHandler(String urlPath, Object handler) throws BeansException, IllegalStateException {
		Assert.notNull(urlPath, "URL path must not be null");
		Assert.notNull(handler, "Handler object must not be null");
		Object resolvedHandler = handler;

		// Eagerly resolve handler if referencing singleton via name.
		if (!this.lazyInitHandlers && handler instanceof String) {
			String handlerName = (String) handler;
			ApplicationContext applicationContext = obtainApplicationContext();
			if (applicationContext.isSingleton(handlerName)) {
				resolvedHandler = applicationContext.getBean(handlerName);
			}
		}

		Object mappedHandler = this.handlerMap.get(urlPath);
		if (mappedHandler != null) {
			if (mappedHandler != resolvedHandler) {
				throw new IllegalStateException(
						"Cannot map " + getHandlerDescription(handler) + " to URL path [" + urlPath +
						"]: There is already " + getHandlerDescription(mappedHandler) + " mapped.");
			}
		}
		else {
			if (urlPath.equals("/")) {
				if (logger.isInfoEnabled()) {
					logger.info("Root mapping to " + getHandlerDescription(handler));
				}
				setRootHandler(resolvedHandler);
			}
			else if (urlPath.equals("/*")) {
				if (logger.isInfoEnabled()) {
					logger.info("Default mapping to " + getHandlerDescription(handler));
				}
				setDefaultHandler(resolvedHandler);
			}
			else {
				this.handlerMap.put(urlPath, resolvedHandler);
				if (logger.isInfoEnabled()) {
					logger.info("Mapped URL path [" + urlPath + "] onto " + getHandlerDescription(handler));
				}
			}
		}
	}

至此URL的映射已完成，下边就是调用了。

调用

入口是DispatcherServlet类的doService方法，：

@Override
	protected void doService(HttpServletRequest request, HttpServletResponse response) throws Exception {
		if (logger.isDebugEnabled()) {
			String resumed = WebAsyncUtils.getAsyncManager(request).hasConcurrentResult() ? " resumed" : "";
			logger.debug("DispatcherServlet with name '" + getServletName() + "'" + resumed +
					" processing " + request.getMethod() + " request for [" + getRequestUri(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 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);
		}

		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);
				}
			}
		}
	}

springmvc优化点：

 

1、Controller 如果能保持单例，尽量使用单例

这样可以减少创建对象和回收对象的开销。也就是说，如果 Controller 的类变量和实例 变量可以以方法形参声明的尽量以方法的形参声明，不要以类变量和实例变量声明，这 样可以避免线程安全问题。

 

2、处理 Request 的方法中的形参务必加上@RequestParam 注解

这样可以避免 Spring MVC 使用 asm 框架读取 class 文件获取方法参数名的过程。即便 Spring MVC 对读取出的方法参数名进行了缓存，如果不要读取 class 文件当然是更好。