SpringBoot 配置 Servlet、Filter、Listener

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.

由上可知，我们可以使用替代方案：ServletContextInitializer

@Configuration
public class GoServletContextInitializer implements ServletContextInitializer {

@Override
public void onStartup(ServletContext servletContext) throws ServletException {

//Log4j Config Listener
servletContext.setInitParameter("log4jConfigLocation", "classpath:config/properties/log4j.properties");
servletContext.addListener(Log4jConfigListener.class);

//CharacterEncodingFilter
FilterRegistration.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, "/*");

//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

第二种方案：ServletContextInitializer 的延伸

请看继承体系



位于最下边的三个类都能实现运行时注册（Servlet、Listener、Filter）

1.ServletRegistrationBean 在系统初始化时向 ServletContext 注册其包含的一个 Servlet，我们可以事先设置它的 Servlet，再把它定义为一个 Bean

2.ServletListenerRegistrationBean 在系统初始化时向 ServletContext 注册其包含的一个 ServletContextListener，我们可以事先设置它的 Listener，再把它定义为一个 Bean

3.AbstractFilterRegistrationBean 通过抽象模板方法 getFilter()，将构建 Filter 的具体细节开放给子类，而其会在系统初始化时向 ServletContext 注册这个 Filter，对此，我们可以定义一个派生类，重写该模板方法以返回我们需要构建的 Filter，最后把它定义为一个 Bean