Spring-MVC源码分析之DispatchServlet初始化DispatchServlet类图结构DispatchServlet

DispatchServlet类图结构

看看调用流程

DispatchServlet初始化方式

Spring官网

• 基于Java类初始化

public class MyWebApplicationInitializer implements WebApplicationInitializer {

    @Override
    public void onStartup(ServletContext servletContext) {

        // Load Spring web application configuration
        AnnotationConfigWebApplicationContext context = new AnnotationConfigWebApplicationContext();
        context.register(AppConfig.class);

        // Create and register the DispatcherServlet
        DispatcherServlet servlet = new DispatcherServlet(context);
        ServletRegistration.Dynamic registration = servletContext.addServlet("app", servlet);
        registration.setLoadOnStartup(1);
        registration.addMapping("/app/*");
    }
}

• 基于XML

在web.xml中定义

<web-app>
   <!--初始化ContextLoaderListener监听器时，加载-->
    <listener>
        <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
    </listener>

    <context-param>
        <param-name>contextConfigLocation</param-name>
        <param-value>/WEB-INF/app-context.xml</param-value>
    </context-param>

    <servlet>
        <servlet-name>app</servlet-name>
        <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
        <init-param>
            <param-name>contextConfigLocation</param-name>
            <param-value></param-value>
        </init-param>
        <load-on-startup>1</load-on-startup>
    </servlet>

    <servlet-mapping>
        <servlet-name>app</servlet-name>
        <url-pattern>/app/*</url-pattern>
    </servlet-mapping>

</web-app>

public class ContextLoaderListener extends ContextLoader implements ServletContextListener {


    /**
	 * Initialize the root web application context.
     * 实现servlet的方法
	 */
	@Override
	public void contextInitialized(ServletContextEvent event) {
		initWebApplicationContext(event.getServletContext());
	}

    public WebApplicationContext initWebApplicationContext(ServletContext servletContext) {
		if (servletContext.getAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE) != null) {
			throw new IllegalStateException(
					"Cannot initialize context because there is already a root application context present - " +
					"check whether you have multiple ContextLoader* definitions in your web.xml!");
		}

		servletContext.log("Initializing Spring root WebApplicationContext");
		Log logger = LogFactory.getLog(ContextLoader.class);
		if (logger.isInfoEnabled()) {
			logger.info("Root WebApplicationContext: initialization started");
		}
		long startTime = System.currentTimeMillis();

		try {
			// Store context in local instance variable, to guarantee that
			// it is available on ServletContext shutdown.
			if (this.context == null) {
				this.context = createWebApplicationContext(servletContext);
			}
			if (this.context instanceof ConfigurableWebApplicationContext) {
				ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) this.context;
				if (!cwac.isActive()) {
					// The context has not yet been refreshed -> provide services such as
					// setting the parent context, setting the application context id, etc
					if (cwac.getParent() == null) {
						// The context instance was injected without an explicit parent ->
						// determine parent for root web application context, if any.
						ApplicationContext parent = loadParentContext(servletContext);
						cwac.setParent(parent);
					}
					configureAndRefreshWebApplicationContext(cwac, servletContext);
				}
			}
			servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, this.context);

			ClassLoader ccl = Thread.currentThread().getContextClassLoader();
			if (ccl == ContextLoader.class.getClassLoader()) {
				currentContext = this.context;
			}
			else if (ccl != null) {
				currentContextPerThread.put(ccl, this.context);
			}

			if (logger.isInfoEnabled()) {
				long elapsedTime = System.currentTimeMillis() - startTime;
				logger.info("Root WebApplicationContext initialized in " + elapsedTime + " ms");
			}

			return this.context;
		}
		catch (RuntimeException | Error ex) {
			logger.error("Context initialization failed", ex);
			servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, ex);
			throw ex;
		}
	}

}

请求如何被DispatchServlet处理的

doDispatchServlet

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 {
                //请求类型：request.getContentType(), "multipart/"  是否是文件上传，如果是的话，将请求转化成文件上传类请求（StandardMultipartHttpServletRequest）
				processedRequest = checkMultipart(request);
				multipartRequestParsed = (processedRequest != request);

				// Determine handler for the current request.（确定当前请求的处理程序）
                //获取请求Controller
				mappedHandler = getHandler(processedRequest);
				if (mappedHandler == null) {
					noHandlerFound(processedRequest, response);
					return;
				}

				// Determine handler adapter for the current request.
                //获取请求适配器（具体的）
				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);
				}
			}
		}
	}

通过请求这里拿到的是一个Handler链，链条里面具体包含请求handler,通过调试可以看见具体的handler就是我们实际的controller

SpringMVC的处理流程

　　①：DispatcherServlet是springmvc中的前端控制器(front controller),负责接收request并将request转发给对应的处理组件.

　　②：HanlerMapping是springmvc中完成url到controller映射的组件.DispatcherServlet接收request,然后从HandlerMapping查找处理request的controller.

　　③：Cntroller处理request,并返回ModelAndView对象,Controller是springmvc中负责处理request的组件(类似于struts2中的Action),ModelAndView是封装结果视图的组件.

　　④ ⑤ ⑥：视图解析器解析ModelAndView对象并返回对应的视图给客户端.

DispatchServlet

private List<HandlerMapping> handlerMappings//如何被初始化的

先看看调用链

1、spring创建beanName=beanNameHandlerMapping的时候

AbstractAutowireCapableBeanFactory.initializeBean
protected Object initializeBean(String beanName, Object bean, @Nullable RootBeanDefinition mbd) {
   if (System.getSecurityManager() != null) {
      AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
         invokeAwareMethods(beanName, bean);
         return null;
      }, getAccessControlContext());
   }
   else {
      //设置beanName，只要实现了Aware接口（具体的有BeanNameAware、BeanClassLoaderAware、BeanFactoryAware）
      invokeAwareMethods(beanName, bean);
   }

   Object wrappedBean = bean;
   if (mbd == null || !mbd.isSynthetic()) {
      //在bean实例化之前调用BeanPostProcessor
      wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
   }

   try {
      invokeInitMethods(beanName, wrappedBean, mbd);
   }
   catch (Throwable ex) {
      throw new BeanCreationException(
            (mbd != null ? mbd.getResourceDescription() : null),
            beanName, "Invocation of init method failed", ex);
   }
   if (mbd == null || !mbd.isSynthetic()) {
      wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
   }

   return wrappedBean;
}

class ApplicationContextAwareProcessor implements BeanPostProcessor {

   private final ConfigurableApplicationContext applicationContext;

   private final StringValueResolver embeddedValueResolver;


   /**
    * Create a new ApplicationContextAwareProcessor for the given context.
    */
   public ApplicationContextAwareProcessor(ConfigurableApplicationContext applicationContext) {
      this.applicationContext = applicationContext;
      this.embeddedValueResolver = new EmbeddedValueResolver(applicationContext.getBeanFactory());
   }


   @Override
   @Nullable
   public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
      if (!(bean instanceof EnvironmentAware || bean instanceof EmbeddedValueResolverAware ||
            bean instanceof ResourceLoaderAware || bean instanceof ApplicationEventPublisherAware ||
            bean instanceof MessageSourceAware || bean instanceof ApplicationContextAware)){
         return bean;
      }
      //非分析的信息删除掉了
      invokeAwareInterfaces(bean);
 
      return bean;
   }

   private void invokeAwareInterfaces(Object bean) {
      if (bean instanceof EnvironmentAware) {
         ((EnvironmentAware) bean).setEnvironment(this.applicationContext.getEnvironment());
      }
      if (bean instanceof EmbeddedValueResolverAware) {
         ((EmbeddedValueResolverAware) bean).setEmbeddedValueResolver(this.embeddedValueResolver);
      }
      if (bean instanceof ResourceLoaderAware) {
         ((ResourceLoaderAware) bean).setResourceLoader(this.applicationContext);
      }
      if (bean instanceof ApplicationEventPublisherAware) {
         ((ApplicationEventPublisherAware) bean).setApplicationEventPublisher(this.applicationContext);
      }
      if (bean instanceof MessageSourceAware) {
         ((MessageSourceAware) bean).setMessageSource(this.applicationContext);
      }
      //这个也就是如果是ApplicationContextAware的实例时，把当前spring上下文设置进去
      if (bean instanceof ApplicationContextAware) {
         ((ApplicationContextAware) bean).setApplicationContext(this.applicationContext);//这里其实调用了ApplicationObjectSupport.setApplicationContext方法，因为他是一个ApplicationContextAware的实例
      }
   }

}

public abstract class ApplicationObjectSupport implements ApplicationContextAware {

@Override
public final void setApplicationContext(@Nullable ApplicationContext context) throws BeansException {
   //其他代码删除
   initApplicationContext(context);
}
}

AbstractDetectingUrlHandlerMapping.initApplicationContext

AbstractDetectingUrlHandlerMapping extends AbstractUrlHandlerMapping

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

protected void detectHandlers() throws BeansException {
        ApplicationContext applicationContext = obtainApplicationContext();
        //在spring上下文中找
        String[] beanNames = (this.detectHandlersInAncestorContexts ?
                BeanFactoryUtils.beanNamesForTypeIncludingAncestors(applicationContext, Object.class) :
                //在spring上下文中获取Object类型的bean然后加载处理
                applicationContext.getBeanNamesForType(Object.class));

        // 遍历beanNames,并找到这些bean对应的url
        for (String beanName : beanNames) {
             找bean上的所有url(controller上的url+方法上的url),该方法由对应的子类实现--this=beanNameHandlerMapping
            String[] urls = determineUrlsForHandler(beanName);//beanNameHandlerMapping.determineUrlsForHandler
            if (!ObjectUtils.isEmpty(urls)) {
                // URL paths found: Let's consider it a handler.
                // 保存urls和beanName的对应关系,put it to Map<urls,beanName>,该方法在父类AbstractUrlHandlerMapping中实现
                registerHandler(urls, beanName);
            }
        }
}

AbstractAutowireCapableBeanFactory.applyBeanPostProcessorsBeforeInitialization
//在创建这个beanName之前，首先先调用
for (BeanPostProcessor processor : getBeanPostProcessors()) { Object current = processor.postProcessBeforeInitialization(result, beanName); if (current == null) { return result; } result = current; }

我们首先看第一个步骤,也就是建立Map<url,controller>关系的部分.第一部分的入口类为ApplicationObjectSupport的setApplicationContext方法.setApplicationContext方法中核心部分就是初始化容器initApplicationContext(context),子类AbstractDetectingUrlHandlerMapping实现了该方法,所以我们直接看子类中的初始化容器方法.

最后

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