SpringMVC源码解析系列2-DispatcherServlet

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DispatcherServlet初始化过程

DispathcerServlet继承关系

可以看到有几个生命周期接口:

  1. ApplicationContextAware:保存了spring上下文

    public interface ApplicationContextAware extends Aware {
	//上下文初始化完成后被调用
	void setApplicationContext(ApplicationContext applicationContext) throws BeansException;
}
#org.springframework.web.servlet.FrameworkServlet	
//保存SpringMVC上下文 当通过Spring装载DispatchServlet时会被调用
@Override
public void setApplicationContext(ApplicationContext applicationContext) {
	if (this.webApplicationContext == null && applicationContext instanceof WebApplicationContext) {
		this.webApplicationContext = (WebApplicationContext) applicationContext;
		this.webApplicationContextInjected = true;
	}
}

  2. EnvironmentAware:保存了环境变量对象

    public interface EnvironmentAware extends Aware {
	//环境变量对象初始化完成后被调用
	void setEnvironment(Environment environment);
}
#org.springframework.web.servlet.HttpServletBean
	@Override
	public void setEnvironment(Environment environment) {
		Assert.isInstanceOf(ConfigurableEnvironment.class, environment, "ConfigurableEnvironment required");
		this.environment = (ConfigurableEnvironment) environment;
	}

  3. Servlet:Servlet生命周期

    public interface Servlet {
   //serlvet初始化
    public void init(ServletConfig config) throws ServletException;
    public ServletConfig getServletConfig();
    public void service(ServletRequest req, ServletResponse res)
            throws ServletException, IOException;
    public String getServletInfo();
  //serlvet销毁
    public void destroy();
}
#org.springframework.web.servlet.HttpServletBean
@Override
public final void init() throws ServletException {
	...
	initServletBean();
}
@Override
public void destroy() {
	if (this.webApplicationContext instanceof ConfigurableApplicationContext && !this.webApplicationContextInjected) {
		//销毁上下文
		((ConfigurableApplicationContext) this.webApplicationContext).close();
	}
}
#org.springframework.web.servlet.FrameworkServlet
DispatcherServlet extends FrameworkServlet 
#org.springframework.web.servlet.FrameworkServlet
@Override
protected final void initServletBean() throws ServletException {
	...
	try {
		this.webApplicationContext = initWebApplicationContext();
		initFrameworkServlet();
	}
	...
}
protected WebApplicationContext initWebApplicationContext() {
	WebApplicationContext rootContext =
			WebApplicationContextUtils.getWebApplicationContext(getServletContext());
	WebApplicationContext wac = null;
	...
	//以spring配置方式时webApplicationContext!=null
	if (this.webApplicationContext != null) {
			wac = this.webApplicationContext;
			if (wac instanceof ConfigurableWebApplicationContext) {
				ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) wac;
						cwac.setParent(rootContext);
				}
			}
		}
	if (wac == null) {
		//创建applicationContext
		wac = createWebApplicationContext(rootContext);
	}
	...
	return wac;
}
protected WebApplicationContext createWebApplicationContext(ApplicationContext parent) {
	//XmlWebApplicationContext 
	Class<?> contextClass = getContextClass();
	...
	//创建applicationContext
	ConfigurableWebApplicationContext wac =
			(ConfigurableWebApplicationContext) BeanUtils.instantiateClass(contextClass);
	wac.setEnvironment(getEnvironment());
	//设置parent(ContextLoadListener中创建的applicationContext)
	wac.setParent(parent);
	//读取contextConfigLocation配置
	wac.setConfigLocation(getContextConfigLocation());
	//refresh()
	configureAndRefreshWebApplicationContext(wac);
	return wac;
}
//当SpringMVC上下初始化完成后会去装载默认策略(HandlerMapping,HandleAdapter)
protected void initStrategies(ApplicationContext context) {
  //获取容器中是否有其实现 没有则加载DispatcherServlet.properties中的默认实现
	initMultipartResolver(context);
	initLocaleResolver(context);
	initThemeResolver(context);
	initHandlerMappings(context);
	initHandlerAdapters(context);
	initHandlerExceptionResolvers(context);
	initRequestToViewNameTranslator(context);
	initViewResolvers(context);
	initFlashMapManager(context);
}

    org.springframework.web.servlet.LocaleResolver=org.springframework.web.servlet.i18n.AcceptHeaderLocaleResolver
org.springframework.web.servlet.ThemeResolver=org.springframework.web.servlet.theme.FixedThemeResolver
org.springframework.web.servlet.HandlerMapping=org.springframework.web.servlet.handler.BeanNameUrlHandlerMapping,\
	org.springframework.web.servlet.mvc.annotation.DefaultAnnotationHandlerMapping
org.springframework.web.servlet.HandlerAdapter=org.springframework.web.servlet.mvc.HttpRequestHandlerAdapter,\
	org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter,\
	org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter
org.springframework.web.servlet.HandlerExceptionResolver=org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerExceptionResolver,\
	org.springframework.web.servlet.mvc.annotation.ResponseStatusExceptionResolver,\
	org.springframework.web.servlet.mvc.support.DefaultHandlerExceptionResolver
org.springframework.web.servlet.RequestToViewNameTranslator=org.springframework.web.servlet.view.DefaultRequestToViewNameTranslator
org.springframework.web.servlet.ViewResolver=org.springframework.web.servlet.view.InternalResourceViewResolver
org.springframework.web.servlet.FlashMapManager=org.springframework.web.servlet.support.SessionFlashMapManager

DispatcherServlet调用过程

@Override
protected void doService(HttpServletRequest request, HttpServletResponse response) throws Exception {
	//将相关配置设置到request作用于中
	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());
  	...
	request.setAttribute(OUTPUT_FLASH_MAP_ATTRIBUTE, new FlashMap());
	request.setAttribute(FLASH_MAP_MANAGER_ATTRIBUTE, this.flashMapManager);

	try {
		doDispatch(request, response);
	}
}

protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
	...
	try {
		ModelAndView mv = null;
		Exception dispatchException = null;
		try {
			processedRequest = checkMultipart(request);
			multipartRequestParsed = (processedRequest != request);
			//1.调用handlerMapping获取handlerChain
			mappedHandler = getHandler(processedRequest);
			if (mappedHandler == null || mappedHandler.getHandler() == null) {
				noHandlerFound(processedRequest, response);
				return;
			}
			// 2.获取支持该handler解析的HandlerAdapter
			HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());
          	//前置处理(CORS时用到)
			if (!mappedHandler.applyPreHandle(processedRequest, response)) {
					return;
				}
			// 3.使用HandlerAdapter完成handler处理
			mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
			//如果是异步请求 直接返回 
			if (asyncManager.isConcurrentHandlingStarted()) {
				return;
			}
			applyDefaultViewName(request, mv);
          	//后置处理
			mappedHandler.applyPostHandle(processedRequest, response, mv);
		}
		catch (Exception ex) {
			dispatchException = ex;
		}
      	//4.异常处理,视图解析,渲染返回
		processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
	}
	...
}
private void processDispatchResult(HttpServletRequest request, HttpServletResponse response,
		HandlerExecutionChain mappedHandler, ModelAndView mv, Exception exception) throws Exception {
	boolean errorView = false;
  	//如果HandlerAdapter.handler()执行异常 则进行异常处理
	if (exception != null) {
		...
          Object handler = (mappedHandler != null ? mappedHandler.getHandler() : null);
      //4.1
        mv = processHandlerException(request, response, handler, exception);
        errorView = (mv != null);
	}


	if (mv != null && !mv.wasCleared()) {
      	//4.2 视图解析 渲染返回
		render(mv, request, response);
		if (errorView) {
			WebUtils.clearErrorRequestAttributes(request);
		}
	}
}
//异常处理
protected ModelAndView processHandlerException(HttpServletRequest request, HttpServletResponse response,
		Object handler, Exception ex) throws Exception {
	ModelAndView exMv = null;
	for (HandlerExceptionResolver handlerExceptionResolver : this.handlerExceptionResolvers) {
      	//使用异常解析器解析异常(类似HandlerAdapter参数解析,调用)
		exMv = handlerExceptionResolver.resolveException(request, response, handler, ex);
		if (exMv != null) {
			break;
		}
    }
  	...
}
protected void render(ModelAndView mv, HttpServletRequest request, HttpServletResponse response) throws Exception {
	//国际化
	Locale locale = this.localeResolver.resolveLocale(request);
	response.setLocale(locale);
	View view;
	if (mv.isReference()) {
		//4.2.1视图解析
		view = resolveViewName(mv.getViewName(), mv.getModelInternal(), locale, request);
		...
	}
	else {
		view = mv.getView();
	}
	....
	try {
		if (mv.getStatus() != null) {
			response.setStatus(mv.getStatus().value());
		}
      	//渲染返回
		view.render(mv.getModelInternal(), request, response);
	}
	...
}
protected View resolveViewName(String viewName, Map<String, Object> model, Locale locale,
		HttpServletRequest request) throws Exception {
	//视图解析
	for (ViewResolver viewResolver : this.viewResolvers) {
		View view = viewResolver.resolveViewName(viewName, locale);
		if (view != null) {
			return view;
		}
	}
	return null;
}

过程概括:

  1. 调用HandlerMapping得到HandlerChain(Handler+Intercept)
  2. 调用HandlerAdapter执行handle过程(参数解析 过程调用)
  3. 异常处理(过程类似HanderAdapter)
  4. 调用ViewResolver进行视图解析
  5. 渲染视图

springmvc流程
上述图片来自网络

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