丽江建设网站,网上国网推广宣传语,最大的建材采购平台,做界面的网站SpringMVC的启动入口在SpringServletContainerInitializer类#xff0c;它是ServletContainerInitializer实现类(Servlet3.0新特性)。在实现方法中使用WebApplicationInitializer创建ApplicationContext、创建注册DispatcherServlet、初始化ApplicationContext等。
SpringMVC…SpringMVC的启动入口在SpringServletContainerInitializer类它是ServletContainerInitializer实现类(Servlet3.0新特性)。在实现方法中使用WebApplicationInitializer创建ApplicationContext、创建注册DispatcherServlet、初始化ApplicationContext等。
SpringMVC已经将大部分的启动逻辑封装在了几个抽象WebApplicationInitializer中开发者只要继承这些抽象类实现抽象方法即可。
本文将详细分析ServletContainerInitializer、SpringServletContainerInitializer和WebApplicationInitializer的工作流程。
Servlet3.0的ServletContainerInitializer
ServletContainerInitializer接口
ServletContainerInitializer是Servlet3.0的接口。
该接口在web应用程序启动阶段接收通知注册servlet、filter、listener等。
该接口的实现类可以用HandlesTypes进行标注并指定一个Class值后续会将实现、扩展了这个Class的类集合作为参数传递给onStartup方法。
以tomcat为例在容器配置初始化阶段将使用SPI查找实现类在ServletContext启动阶段初始化并调用onStartup方法来进行ServletContext的初始化。
SpringServletContainerInitializer实现类
在onStartup方法创建所有的WebApplicationInitializer对并调用onStartup方法。
以下为SPI配置在spring-web/src/main/resources/META-INF/services/javax.servlet.ServletContainerInitializer文件 WebApplicationInitializer接口
WebApplicationInitializer接口概述
Interface to be implemented in Servlet 3.0 environments in order to configure the ServletContext programmatically – as opposed to (or possibly in conjunction with) the traditional web.xml-based approach.
Implementations of this SPI will be detected automatically by SpringServletContainerInitializer, which itself is bootstrapped automatically by any Servlet 3.0 container. See its Javadoc for details on this bootstrapping mechanism.
示例
public class MyWebAppInitializer implements WebApplicationInitializer {Overridepublic void onStartup(ServletContext container) {// Create the root Spring application contextAnnotationConfigWebApplicationContext rootContext new AnnotationConfigWebApplicationContext();rootContext.register(AppConfig.class);// Manage the lifecycle of the root application contextcontainer.addListener(new ContextLoaderListener(rootContext));// Create the dispatcher servlets Spring application contextAnnotationConfigWebApplicationContext dispatcherContext new AnnotationConfigWebApplicationContext();dispatcherContext.register(DispatcherConfig.class);// Register and map the dispatcher servletServletRegistration.Dynamic dispatcher container.addServlet(dispatcher, new DispatcherServlet(dispatcherContext));dispatcher.setLoadOnStartup(1);dispatcher.addMapping(/);}
}开发者可以编写类继承AbstractAnnotationConfigDispatcherServletInitializer抽象类这个抽象类已经将大部分的初始化逻辑进行了封装。
WebApplicationInitializer实现和继承关系 AbstractContextLoaderInitializer类
Convenient base class for WebApplicationInitializer implementations that register a ContextLoaderListener in the servlet context. The only method required to be implemented by subclasses is createRootApplicationContext(), which gets invoked from registerContextLoaderListener(ServletContext).
AbstractDispatcherServletInitializer类
Base class for WebApplicationInitializer implementations that register a DispatcherServlet in the servlet context. Most applications should consider extending the Spring Java config subclass AbstractAnnotationConfigDispatcherServletInitializer.
AbstractAnnotationConfigDispatcherServletInitializer类
WebApplicationInitializer to register a DispatcherServlet and use Java-based Spring configuration. Implementations are required to implement:
getRootConfigClasses() – for “root” application context (non-web infrastructure) configuration.getServletConfigClasses() – for DispatcherServlet application context (Spring MVC infrastructure) configuration.
If an application context hierarchy is not required, applications may return all configuration via getRootConfigClasses() and return null from getServletConfigClasses().
开发者SpringMvcInitializer示例
开发者需要编写类继承AbstractAnnotationConfigDispatcherServletInitializer类实现几个抽象方法
public class SpringMvcInitializer extends AbstractAnnotationConfigDispatcherServletInitializer {/*** 指定创建root application context需要的Configuration/Component类*/Overrideprotected Class?[] getRootConfigClasses() {return new Class[]{AppConfig.class};}/*** 指定创建Servlet application context需要的Configuration/Component类* 如果所有的配置类都使用root config classes就返回null*/Overrideprotected Class?[] getServletConfigClasses() {return null;}/*** Specify the servlet mapping(s) for the DispatcherServlet — for example /, /app, etc.*/Overrideprotected String[] getServletMappings() {return new String[]{/};}
}SpringMVC启动流程
入口AbstractDispatcherServletInitializer.onStartup方法
public void onStartup(ServletContext servletContext) throws ServletException {super.onStartup(servletContext);registerDispatcherServlet(servletContext);
}父类的onStartup方法创建RootApplicationContext、注册ContextLoaderListener监听器
public void onStartup(ServletContext servletContext) throws ServletException {registerContextLoaderListener(servletContext);
}protected void registerContextLoaderListener(ServletContext servletContext) {WebApplicationContext rootAppContext createRootApplicationContext();if (rootAppContext ! null) {// ContextLoaderListener是ServletContextListener// 会在contextInitialized阶段初始化RootApplicationContextContextLoaderListener listener new ContextLoaderListener(rootAppContext);listener.setContextInitializers(getRootApplicationContextInitializers());servletContext.addListener(listener);}
}注册DispatcherServlet
registerDispatcherServlet方法用于创建ServletApplicationContext、注册DispatcherServlet
protected void registerDispatcherServlet(ServletContext servletContext) {String servletName getServletName();// 创建ServletApplicationContextWebApplicationContext servletAppContext createServletApplicationContext();// 创建DispatcherServletFrameworkServlet dispatcherServlet createDispatcherServlet(servletAppContext);// 添加ApplicationContextInitializer集会在初始化时调用dispatcherServlet.setContextInitializers(getServletApplicationContextInitializers());// 添加到ServletContextServletRegistration.Dynamic registration servletContext.addServlet(servletName, dispatcherServlet);registration.setLoadOnStartup(1);registration.addMapping(getServletMappings());registration.setAsyncSupported(isAsyncSupported());Filter[] filters getServletFilters();if (!ObjectUtils.isEmpty(filters)) {for (Filter filter : filters) {registerServletFilter(servletContext, filter);}}customizeRegistration(registration);
}触发ContextLoaderListener监听器contextInitialized事件
这个是Servlet的ServletContextListener机制在ServletContext创建之后触发contextInitialized事件
public void contextInitialized(ServletContextEvent event) {initWebApplicationContext(event.getServletContext());
}public WebApplicationContext initWebApplicationContext(ServletContext servletContext) {// 判断是否已经在当前ServletContext绑定了WebApplicationContext// 如果已经绑定抛错if (servletContext.getAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE) ! null) {throw new IllegalStateException(已经初始化过了);}try {if (this.context null) {this.context createWebApplicationContext(servletContext);}if (this.context instanceof ConfigurableWebApplicationContext) {ConfigurableWebApplicationContext cwac (ConfigurableWebApplicationContext) this.context;if (!cwac.isActive()) {if (cwac.getParent() null) {ApplicationContext parent loadParentContext(servletContext);cwac.setParent(parent);}// refreshconfigureAndRefreshWebApplicationContext(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);}return this.context;} catch (RuntimeException | Error ex) {servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, ex);throw ex;}
}protected void configureAndRefreshWebApplicationContext(ConfigurableWebApplicationContext wac, ServletContext sc) {// 给wac设置idwac.setServletContext(sc);// 设置spring主配置文件路径String configLocationParam sc.getInitParameter(CONFIG_LOCATION_PARAM);if (configLocationParam ! null) {wac.setConfigLocation(configLocationParam);}ConfigurableEnvironment env wac.getEnvironment();if (env instanceof ConfigurableWebEnvironment) {((ConfigurableWebEnvironment) env).initPropertySources(sc, null);}customizeContext(sc, wac);// 刷新ApplicationContextwac.refresh();
}触发DispatcherServlet的init事件
Servlet在接收请求之前会调用其init方法进行初始化这个是Servlet的规范。
init方法在其父类HttpServletBean中
public final void init() throws ServletException {// 从ServletConfig获取配置设置到ServletPropertyValues pvs new ServletConfigPropertyValues(getServletConfig(), this.requiredProperties);if (!pvs.isEmpty()) {try {BeanWrapper bw PropertyAccessorFactory.forBeanPropertyAccess(this);ResourceLoader resourceLoader new ServletContextResourceLoader(getServletContext());bw.registerCustomEditor(Resource.class, new ResourceEditor(resourceLoader, getEnvironment()));initBeanWrapper(bw);bw.setPropertyValues(pvs, true);} catch (BeansException ex) {throw ex;}}// 初始化initServletBean();
}// FrameworkServlet
protected final void initServletBean() throws ServletException {try {// 初始化ServletApplicationContextthis.webApplicationContext initWebApplicationContext();initFrameworkServlet();} catch (ServletException | RuntimeException ex) {throw ex;}
}protected WebApplicationContext initWebApplicationContext() {// 获取rootApplicationContext// 之前的ServletContext初始化阶段已经绑定WebApplicationContext rootContext WebApplicationContextUtils.getWebApplicationContext(getServletContext());WebApplicationContext wac null;if (this.webApplicationContext ! null) {wac this.webApplicationContext;if (wac instanceof ConfigurableWebApplicationContext) {ConfigurableWebApplicationContext cwac (ConfigurableWebApplicationContext) wac;if (!cwac.isActive()) {// 将rootApplicationContext设置为Parentif (cwac.getParent() null) {cwac.setParent(rootContext);}// 刷新ApplicationContextconfigureAndRefreshWebApplicationContext(cwac);}}}// 如果没有需要查找或创建if (wac null) {wac findWebApplicationContext();}if (wac null) {wac createWebApplicationContext(rootContext);}if (!this.refreshEventReceived) {synchronized (this.onRefreshMonitor) {// 子类实现onRefresh(wac);}}if (this.publishContext) {String attrName getServletContextAttributeName();getServletContext().setAttribute(attrName, wac);}return wac;
}// DispatcherServlet
protected void onRefresh(ApplicationContext context) {initStrategies(context);
}// 初始化SpringMVC相关组件
protected void initStrategies(ApplicationContext context) {initMultipartResolver(context);initLocaleResolver(context);initThemeResolver(context);initHandlerMappings(context);initHandlerAdapters(context);initHandlerExceptionResolvers(context);initRequestToViewNameTranslator(context);initViewResolvers(context);initFlashMapManager(context);
}SpringMVC启动流程总结
创建RootApplicationContext、注册ContextLoaderListener监听器创建ServletApplicationContext、注册DispatcherServlet触发ContextLoaderListener监听器contextInitialized事件初始化RootApplicationContext触发DispatcherServlet的init事件初始化ServletApplicationContext
