Springmvc入門（十）DispatcherServlet初始化源碼分析

DispatchServlet作為springmvc核心類，以下是它的結構圖

Aware接口，比如實作了

ApplicationContextAware

接口的類，能夠擷取到

ApplicationContext。

DispatcherServer的構造器

先初始化父類的，然後設定一個父類屬性的值，将http請求直接發送到doService方法

public DispatcherServlet() {
		super();
        //設定屬性，是否将http請求發送到doService方法
		setDispatchOptionsRequest(true);
	}


	public DispatcherServlet(WebApplicationContext webApplicationContext) {
		super(webApplicationContext);
		setDispatchOptionsRequest(true);
	}
           

FrameworkServlet的構造器，繼續對父類的HttpServletBean類進行建構

public FrameworkServlet() {
	}

	public FrameworkServlet(WebApplicationContext webApplicationContext) {
		this.webApplicationContext = webApplicationContext;
	}
           

HttpServletBean中的init初始化方法

init中調用了兩個模闆方法，可以由子類去實作

initServletBean就是子類FrameworkServlet的入口方法

@Override
	public final void init() throws ServletException {
		if (logger.isDebugEnabled()) {
			logger.debug("Initializing servlet '" + getServletName() + "'");
		}

		//将servlet的參數封裝到pvs中，requiredProperties是必須參數
		PropertyValues pvs = new ServletConfigPropertyValues(getServletConfig(), this.requiredProperties);
		if (!pvs.isEmpty()) {
			try {
				//建立并給DispatchServlet指派
				BeanWrapper bw = PropertyAccessorFactory.forBeanPropertyAccess(this);
				ResourceLoader resourceLoader = new ServletContextResourceLoader(getServletContext());
				bw.registerCustomEditor(Resource.class, new ResourceEditor(resourceLoader, getEnvironment()));
				//可以由子類實作，初始化工作
				initBeanWrapper(bw);
				//配置初始化值
				bw.setPropertyValues(pvs, true);
			}
			catch (BeansException ex) {
				if (logger.isErrorEnabled()) {
					logger.error("Failed to set bean properties on servlet '" + getServletName() + "'", ex);
				}
				throw ex;
			}
		}

		//調用子類方法
		initServletBean();

		if (logger.isDebugEnabled()) {
			logger.debug("Servlet '" + getServletName() + "' configured successfully");
		}
	}
	
	protected void initBeanWrapper(BeanWrapper bw) throws BeansException {
	}

	
	protected void initServletBean() throws ServletException {
	}
           

FrameworkServlet的initServletBean的方法

initFrameworkServlet也是一個模闆方法，由子類提供實作，不過子類沒實作

onRefresh模闆方法，子類提供

@Override
	protected final void initServletBean() throws ServletException {
		//開始初始化工作
		getServletContext().log("Initializing Spring FrameworkServlet '" + getServletName() + "'");
		if (this.logger.isInfoEnabled()) {
			this.logger.info("FrameworkServlet '" + getServletName() + "': initialization started");
		}
		long startTime = System.currentTimeMillis();

		try {
			//初始化WebApplicationContext
			this.webApplicationContext = initWebApplicationContext();
			//子類可覆寫此方法，做一些初始化工作，不過子類沒實作
			initFrameworkServlet();
		}
		catch (ServletException | RuntimeException ex) {
			this.logger.error("Context initialization failed", ex);
			throw ex;
		}

		if (this.logger.isInfoEnabled()) {
			long elapsedTime = System.currentTimeMillis() - startTime;
			this.logger.info("FrameworkServlet '" + getServletName() + "': initialization completed in " +
					elapsedTime + " ms");
		}
	}
	
	protected WebApplicationContext initWebApplicationContext() {
		//擷取rootContext
		WebApplicationContext rootContext =
				WebApplicationContextUtils.getWebApplicationContext(getServletContext());
		WebApplicationContext wac = null;
		//如果已經通過構造方法構造了webApplicationContext
		if (this.webApplicationContext != null) {
			wac = this.webApplicationContext;
			if (wac instanceof ConfigurableWebApplicationContext) {
				ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) wac;
				if (!cwac.isActive()) {			
					if (cwac.getParent() == null) {	
						cwac.setParent(rootContext);
					}
					configureAndRefreshWebApplicationContext(cwac);
				}
			}
		}
		if (wac == null) {
			//當webApplicationContext已經存在servletContext，通過servlet配置的參數進行擷取
			wac = findWebApplicationContext();
		}
		if (wac == null) {
			//不存在，則創一個webApplicationContext
			wac = createWebApplicationContext(rootContext);
		}
		if (!this.refreshEventReceived) {
		//當ContextRefreshedEvent沒有觸發時調用此方法
		//子類DispatchServlet類方法的入口
			onRefresh(wac);
		}

		if (this.publishContext) {
			//将applicationContext放入ServletContext	
			String attrName = getServletContextAttributeName();
			getServletContext().setAttribute(attrName, wac);
			if (this.logger.isDebugEnabled()) {
				this.logger.debug("Published WebApplicationContext of servlet '" + getServletName() +
						"' as ServletContext attribute with name [" + attrName + "]");
			}
		}
		return wac;
	}
	
	protected void initFrameworkServlet() throws ServletException {
	}
           

DispatcherServlet的onRefresh方法對自己的九大元件進行初始化

@Override
	protected void onRefresh(ApplicationContext context) {
		initStrategies(context);
	}

	
	protected void initStrategies(ApplicationContext context) {
	//初始化DispatchServlet的九大元件
		initMultipartResolver(context);
		initLocaleResolver(context);
		initThemeResolver(context);
		initHandlerMappings(context);
		initHandlerAdapters(context);
		initHandlerExceptionResolvers(context);
		initRequestToViewNameTranslator(context);
		initViewResolvers(context);
		initFlashMapManager(context);
	}

	
	private void initMultipartResolver(ApplicationContext context) {
		//假設有配置多部分檔案傳輸
		try {
			this.multipartResolver = context.getBean(MULTIPART_RESOLVER_BEAN_NAME, MultipartResolver.class);
			if (logger.isDebugEnabled()) {
				logger.debug("Using MultipartResolver [" + this.multipartResolver + "]");
			}
		}
		catch (NoSuchBeanDefinitionException ex) {
			// 預設是沒有
			this.multipartResolver = null;
			if (logger.isDebugEnabled()) {
				logger.debug("Unable to locate MultipartResolver with name '" + MULTIPART_RESOLVER_BEAN_NAME +
						"': no multipart request handling provided");
			}
		}
	}

	
	private void initThemeResolver(ApplicationContext context) {
		try {
			//再context中擷取，隻要在配置檔案中配置了bean，就能找到
			this.themeResolver = context.getBean(THEME_RESOLVER_BEAN_NAME, ThemeResolver.class);
			if (logger.isDebugEnabled()) {
				logger.debug("Using ThemeResolver [" + this.themeResolver + "]");
			}
		}
		catch (NoSuchBeanDefinitionException ex) {
			// 假設沒有，則使用預設是主題解析類
			//再dispatch.properties可知，預設的主題解析類org.springframework.web.servlet.theme.FixedThemeResolver
			this.themeResolver = getDefaultStrategy(context, ThemeResolver.class);
			if (logger.isDebugEnabled()) {
				logger.debug("Unable to locate ThemeResolver with name '" + THEME_RESOLVER_BEAN_NAME +
						"': using default [" + this.themeResolver + "]");
			}
		}
	}
           

小結：

HttpServletBean繼承HttpServlet，是将servlet中的配置的參數映射到相對應的屬性上，FrameworkServlet主要是建立并初始化WebApplicationContext，DispatcherServlet初始化了自身的九大元件，采用了大量的模闆方法，由父類去調用子類的方法。