在SpringBoot应用中，嵌入式的 Servlet 3.0+ 容器不会直接使用 ServletContainerInitializer 和 WebApplicationInitializer，即通过以上两个接口实现的 Servlet、Filter、Listener 配置都是无效的，这是为了防止第三方代码的设计损坏应用程序，原文如下
Embedded servlet containers will not directly execute the Servlet 3.0+ javax.servlet.ServletContainerInitializer interface, or Spring’s org.springframework.web.WebApplicationInitializer interface. This is an intentional design decision intended to reduce the risk that 3rd party libraries designed to run inside a war will break Spring Boot applications.
If you need to perform servlet context initialization in a Spring Boot application, you should register a bean that implements the org.springframework.boot.context.embedded.ServletContextInitializer interface. The single onStartup method provides access to the ServletContext, and can easily be used as an adapter to an existing WebApplicationInitializer if necessary.
综上，可以采取以下配置
配置策略一：ServletContextInitializer
由官方原文可知，我们可以使用替代方案：ServletContextInitializer，示例如下
@Configuration
public class GoServletContextInitializer implements ServletContextInitializer {@Overridepublic void onStartup(ServletContext servletContext) throws ServletException {//配置 Log4j Config Listener servletContext.setInitParameter("log4jConfigLocation", "classpath:config/properties/log4j.properties"); servletContext.addListener(Log4jConfigListener.class); //配置 CharacterEncodingFilterFilterRegistration.Dynamic characterEncodingFilter =servletContext.addFilter("characterEncodingFilter", CharacterEncodingFilter.class);characterEncodingFilter.setInitParameter("encoding", "UTF-8");characterEncodingFilter.setInitParameter("forceEncoding", "true");characterEncodingFilter.addMappingForUrlPatterns(EnumSet.of(DispatcherType.REQUEST, DispatcherType.FORWARD, DispatcherType.INCLUDE),false, "/*");//配置 statViewServlet StatViewServlet statViewServlet = new StatViewServlet();ServletRegistration.Dynamic dynamic = servletContext.addServlet("statViewServlet", statViewServlet);dynamic.setLoadOnStartup(2);dynamic.addMapping("/druid/*");}
}
亲测，即使将 Spring Boot 打包成 war，并部署到 Tomcat 8.5，这份配置也是有效的
配置策略二：ServletContextInitializer 的延伸
请看类继承体系
原理：最下边的三个子类会自动在运行时注册 Servlet、Listener、Filter（一定要将其定义为 Spring 容器的 Bean）
- ServletRegistrationBean：在Servlet容器初始化时，向 ServletContext 注册一个自定义的 Servlet
- ServletListenerRegistrationBean：在Servlet容器初始化时，向 ServletContext 注册一个自定义的 ServletContextListener
- AbstractFilterRegistrationBean：（模板方法模式）通过模板方法 getFilter()，将 Filter 的构建过程延迟到子类，并在Servlet容器初始化时，向 ServletContext 注册该 Filter。开发者可以定义一个子类来重写该模板方法，以配置一个自定义的 Filter。
Servlet 配置示例
@Configuration
public class ServletConfig {//配置 StatViewServlet@Beanpublic ServletRegistrationBean servletRegistration0() {ServletRegistrationBean registration = new ServletRegistrationBean(new StatViewServlet());registration.addUrlMappings("/druid/*");registration.setLoadOnStartup(0);return registration;}
}
Filter 配置示例
@Configuration
public class FilterConfig {//配置 CharacterEncodingFilter@Beanpublic FilterRegistrationBean filterRegistration1() {FilterRegistrationBean registration = new FilterRegistrationBean(new CharacterEncodingFilter());registration.addUrlPatterns("/*");Map<String, String> initParameters = Maps.newHashMap();initParameters.put("encoding", "UTF-8");initParameters.put("forceEncoding", "true");registration.setInitParameters(initParameters);return registration;}
}
Listener 配置示例
@Configuration
public class ListenerConfig {//配置 RequestContextListener@Beanpublic ServletListenerRegistrationBean<RequestContextListener> listenerRegistration3() {return new ServletListenerRegistrationBean<>(new RequestContextListener());}
}SpringBoot 中配置 Servlet、Filter、Listener源码 OnRefresh()中 调用createWeb()....调用ServletWebServerApplicationContext.selfInitialize方法中getServletContextInitializerBeans中完成从spring容器中把Servlet、Filter、Listener封装成ServletContextInitializer接口实例，后再调用ServletContextInitializer的实例方法onStartUp，完成Servlet、Filter、Listener配置。