DispatcherServlet详细分析

1. DispatcherServlet的作用分析

1.1 uml类图

从类图, 可以看出DispatcherServlet其本质是Servlet, 其间接实现了ServletConfig:

public interface Servlet {void init(ServletConfig var1) throws ServletException;ServletConfig getServletConfig();void service(ServletRequest var1, ServletResponse var2) throws ServletException, IOException;String getServletInfo();void destroy();
}public interface ServletConfig {String getServletName();ServletContext getServletContext();String getInitParameter(String var1);Enumeration<String> getInitParameterNames();
}

2. DispatcherServlet的初始化分析

2.1 初始化流程

解析是从web.xml开始, DispatcherServlet其本质是Servlet, 所以初始化是从Servlet.init()方法开始:

2.2 详细分析流程

下面从上面几个重要步骤详细分析, 初始化的工作:

GenericServlet: init(ServletConfig config)

public void init(ServletConfig config) throws ServletException {this.config = config;this.init();//调用被子类HttpServletBean重写方法init()
}

HttpServletBean: init()

为DispatcherServlet创建BeanWrapper, 从ServletConfig中获取Servlet的initParams, 并设置到BeanWrapper的PropertyValues中去, 如contextConfigLocation字段等属性. 核心代码如下:

PropertyValues pvs = new HttpServletBean.ServletConfigPropertyValues(this.getServletConfig(), this.requiredProperties);
BeanWrapper bw = PropertyAccessorFactory.forBeanPropertyAccess(this);
ResourceLoader resourceLoader = new ServletContextResourceLoader(this.getServletContext());bw.registerCustomEditor(Resource.class, new ResourceEditor(resourceLoader, this.getEnvironment()));
this.initBeanWrapper(bw);
bw.setPropertyValues(pvs, true);

<servlet><servlet-name>webServlet</servlet-name><servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class><init-param><param-name>contextConfigLocation</param-name><param-value>classpath:web-appcontext.xml</param-value></init-param><load-on-startup>1</load-on-startup></servlet>

FrameworkServlet: initWebApplicationContext()

创建并初始化WebApplicationContext (以下简称Mvc容器)

protected WebApplicationContext initWebApplicationContext() {WebApplicationContext rootContext = WebApplicationContextUtils.getWebApplicationContext(this.getServletContext());//父容器if (wac == null) {wac = this.createWebApplicationContext(rootContext);}if (!this.refreshEventReceived) {this.onRefresh(wac);}if (this.publishContext) {//FrameworkServlet.class.getName() + ".CONTEXT."+getServletName()String attrName = this.getServletContextAttributeName();this.getServletContext().setAttribute(attrName, wac);}return wac;
}protected WebApplicationContext createWebApplicationContext(ApplicationContext parent) {Class<?> contextClass = this.getContextClass();//未配置则默认为XmlWebApplicationContextConfigurableWebApplicationContext wac = (ConfigurableWebApplicationContext)BeanUtils.instantiateClass(contextClass);//初始化wac.setEnvironment(this.getEnvironment());//设置Environmentwac.setParent(parent);//设置父容器wac.setConfigLocation(this.getContextConfigLocation()); //设置Spring配置文件位置this.configureAndRefreshWebApplicationContext(wac);return wac;
}protected void configureAndRefreshWebApplicationContext(ConfigurableWebApplicationContext wac){wac.setServletContext(this.getServletContext());//关联ServletContextwac.setServletConfig(this.getServletConfig());wac.setNamespace(this.getNamespace());//设置nameSpace为DispatcherServlet的nameSpacewac.addApplicationListener(new SourceFilteringListener(wac, new FrameworkServlet.ContextRefreshListener()));ConfigurableEnvironment env = wac.getEnvironment();//设置Environmentif (env instanceof ConfigurableWebEnvironment) {((ConfigurableWebEnvironment)env).initPropertySources(this.getServletContext(), this.getServletConfig());}this.postProcessWebApplicationContext(wac);this.applyInitializers(wac);wac.refresh();//初始化所有的bean
}

这里需要注意以下几个点:

1.如果在web.xml中配置了ContextLoaderListener, 则生成的Root ApplicationContext(以下简称Root容器)会从ServletContext属性里拿出来作为当前Mvc容器的parent父容器, 见代码:

public interface WebApplicationContext extends ApplicationContext {String ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE = WebApplicationContext.class.getName() + ".ROOT";//Root WebApplicationContext放在ServletContext属性里
public static WebApplicationContext getWebApplicationContext(ServletContext sc) {return getWebApplicationContext(sc, WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE);}
}

Mvc容器也放在ServletContext属性里, 属性名称为FrameworkServlet.class.getName() + ".CONTEXT."+getServletName()

2.设置Mvc容器的contextConfigLocation

需要注意一个点, 如果web.xml没有配置文件, 最终Mvc容器配置文件默认取${servlet-name}-servlet.xml, 请参考: SpringMVC的默认配置文件位置

DispatcherServlet: initStrategies()

主要的动作是初始化DispatcherServlet的9大对象, 从Mvc容器获取对应类型的对象, 部分找不到会有默认值

protected void initStrategies(ApplicationContext context) {this.initMultipartResolver(context);//无默认值this.initLocaleResolver(context);//有默认值this.initThemeResolver(context);//有默认值this.initHandlerMappings(context);//有默认值this.initHandlerAdapters(context);//有默认值this.initHandlerExceptionResolvers(context);//有默认值this.initRequestToViewNameTranslator(context);//有默认值this.initViewResolvers(context);//有默认值this.initFlashMapManager(context);//有默认值
}

各组件的默认值在DispatcherServlet.properties里定义.

org.springframework.web.servlet.LocaleResolver=org.springframework.web.servlet.i18n.AcceptHeaderLocaleResolverorg.springframework.web.servlet.ThemeResolver=org.springframework.web.servlet.theme.FixedThemeResolverorg.springframework.web.servlet.HandlerMapping=org.springframework.web.servlet.handler.BeanNameUrlHandlerMapping,\org.springframework.web.servlet.mvc.annotation.DefaultAnnotationHandlerMappingorg.springframework.web.servlet.HandlerAdapter=org.springframework.web.servlet.mvc.HttpRequestHandlerAdapter,\org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter,\org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapterorg.springframework.web.servlet.HandlerExceptionResolver=org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerExceptionResolver,\org.springframework.web.servlet.mvc.annotation.ResponseStatusExceptionResolver,\org.springframework.web.servlet.mvc.support.DefaultHandlerExceptionResolverorg.springframework.web.servlet.RequestToViewNameTranslator=org.springframework.web.servlet.view.DefaultRequestToViewNameTranslatororg.springframework.web.servlet.ViewResolver=org.springframework.web.servlet.view.InternalResourceViewResolverorg.springframework.web.servlet.FlashMapManager=org.springframework.web.servlet.support.SessionFlashMapManager

WebApplicationContext.refresh()

WebApplicationContext.refresh和普通的ApplicationContext.refresh相比, 有所增强

AbstractApplicationContext.java

public void refresh() throws BeansException, IllegalStateException {synchronized(this.startupShutdownMonitor) {this.prepareRefresh();ConfigurableListableBeanFactory beanFactory = this.obtainFreshBeanFactory();this.prepareBeanFactory(beanFactory);try {this.postProcessBeanFactory(beanFactory);//增强的方法this.invokeBeanFactoryPostProcessors(beanFactory);this.registerBeanPostProcessors(beanFactory);this.initMessageSource();this.initApplicationEventMulticaster();this.onRefresh();this.registerListeners();this.finishBeanFactoryInitialization(beanFactory);this.finishRefresh();} catch (BeansException var5) {//略}}}

AbstractRefreshableWebApplicationContext.java

protected void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) {beanFactory.addBeanPostProcessor(new ServletContextAwareProcessor(this.servletContext, this.servletConfig));beanFactory.ignoreDependencyInterface(ServletContextAware.class);beanFactory.ignoreDependencyInterface(ServletConfigAware.class);//注册request/session/globalSession等scope相关组件到Mvc容器WebApplicationContextUtils.registerWebApplicationScopes(beanFactory, this.servletContext);//将servlet相关组件注册到Mvc容器WebApplicationContextUtils.registerEnvironmentBeans(beanFactory, this.servletContext, this.servletConfig);
}

ServletContextAwareProcessor.java

public class ServletContextAwareProcessor implements BeanPostProcessor {private ServletContext servletContext;private ServletConfig servletConfig;public ServletContextAwareProcessor(ServletContext servletContext, ServletConfig servletConfig) {this.servletContext = servletContext;this.servletConfig = servletConfig;if (servletContext == null && servletConfig != null) {this.servletContext = servletConfig.getServletContext();}}public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {if (this.servletContext != null && bean instanceof ServletContextAware) {((ServletContextAware)bean).setServletContext(this.servletContext);}if (this.servletConfig != null && bean instanceof ServletConfigAware) {((ServletConfigAware)bean).setServletConfig(this.servletConfig);}return bean;}
}

3. DispatcherServlet的请求过程分析

DispatcherServlet其本质是Servlet, 请求从web容器请求过来调用Servlet的service方法:

3.1 从Servlet调用到DispatcherServlet流程

Servlet.service() -> DispatcherServlet.doDispatch()

下图调用流程比较简单, 略

3.2 DispatcherServlet.doDispatch详细流程

贴出烂大街的处理流程图:

对应源码:

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 {//如果是上传请求,且注册了MultipartResolver//此处会解析文件绑定到request,替换request为MultipartRequestprocessedRequest = this.checkMultipart(request);multipartRequestParsed = processedRequest != request;//如果是@Controller类型的处理器,此处还有校验@RequestMapping注解的三个属性RequestMethod/Headers/ParamsmappedHandler = this.getHandler(processedRequest, false);//获取Handlerif (mappedHandler == null || mappedHandler.getHandler() == null) {this.noHandlerFound(processedRequest, response);return;}//获取HandlerAdapterHandlerAdapter ha = this.getHandlerAdapter(mappedHandler.getHandler());String method = request.getMethod();//interceptors过滤器前置处理if (!mappedHandler.applyPreHandle(processedRequest, response)) {return;}//调用实际Handler处理请求mv = ha.handle(processedRequest, response, mappedHandler.getHandler());this.applyDefaultViewName(request, mv);mappedHandler.applyPostHandle(processedRequest, response, mv);//过滤器后置} catch (Exception var20) {dispatchException = var20;}//渲染view或处理异常this.processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);} catch (Exception e){//略}
}