前言

本文章将介绍SpringBoot注册Servlet的三大组件

一、介绍

由于SpringBoot默认是以jar包的方式运行嵌入式Servlet容器来启动应用，没有web.xml文件，
所以Spring提供以下Bean来注册三大组件。

ServletRegistrationBean 注册自定义Servlet
FilterRegistrationBean 注册自定义Filter
ServletListenerRegistrationBean 注册自定义Listener

二、注入Bean

2.1.ServletRegistrationBean

首先我们需要一个类继承至HttpServlet

public class MyServlet extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {System.out.println("get请求进入servlet");resp.getWriter().println("<h1>get:hello world</h1>");}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {System.out.println("post请求进入servlet");resp.getWriter().println("<h1>post:hello world</h1>");}
}

然后在配置类中注入ServletRegistrationBean

@Configuration
public class SpringBootConfig {
@Beanpublic ServletRegistrationBean doRegiste(){ServletRegistrationBean bean = new ServletRegistrationBean();//将自己创建的继承至HttpServlet的类添加进ServletRegistrationBean bean.setServlet(new MyServlet());//设置请求路径bean.setUrlMappings(Arrays.asList("/myServlet"));//设置优先级bean.setLoadOnStartup(1);return bean;}
}

2.2.FilterRegistrationBean

首先我们需要一个类实现Filter接口，重写它的doFilter方法

public class MyFilter implements Filter {@Overridepublic void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {System.out.println("============请求过滤");request.setCharacterEncoding("utf-8");//分水岭chain.doFilter(request, response);response.setCharacterEncoding("utf-8");System.out.println("============响应过滤");}
}

在配置类中将FilterRegistrationBean注入

@Configuration
public class SpringBootConfig {//注册Servlet//替换：@WebServlet(urlPatterns = "/myServlet")@Beanpublic ServletRegistrationBean doRegiste(){ServletRegistrationBean bean = new ServletRegistrationBean();bean.setServlet(new MyServlet());bean.setUrlMappings(Arrays.asList("/myServlet"));bean.setLoadOnStartup(1);return bean;}//注册Filter//替换//@WebFilter(urlPatterns = {"/*"})@Beanpublic FilterRegistrationBean doFilter(){FilterRegistrationBean bean = new FilterRegistrationBean();bean.setFilter(new MyFilter());bean.addUrlPatterns("/*");return bean;}
}

2.3.ServletListenerRegistrationBean

首先需要一个类实现ServletContextListener接口，重现它的contextInitialized和contextDestroyed方法监听程序初始化和销毁

public class MyListener implements ServletContextListener {@Overridepublic void contextInitialized(ServletContextEvent sce) {ServletContextListener.super.contextInitialized(sce);System.out.println("-------------MyListener inited !");}@Overridepublic void contextDestroyed(ServletContextEvent sce) {ServletContextListener.super.contextDestroyed(sce);System.out.println("----------------MyListener Destroy !");}
}

在配置类中注入ServletListenerRegistrationBean

@Configuration
public class SpringBootConfig {//注册Servlet//替换：@WebServlet(urlPatterns = "/myServlet")@Beanpublic ServletRegistrationBean doRegiste(){ServletRegistrationBean bean = new ServletRegistrationBean();bean.setServlet(new MyServlet());bean.setUrlMappings(Arrays.asList("/myServlet"));bean.setLoadOnStartup(1);return bean;}//注册Filter//替换//@WebFilter(urlPatterns = {"/*"})@Beanpublic FilterRegistrationBean doFilter(){FilterRegistrationBean bean = new FilterRegistrationBean();bean.setFilter(new MyFilter());bean.addUrlPatterns("/*");return bean;}//注册Listener//替换//@WebListener@Beanpublic ServletListenerRegistrationBean doListener(){ServletListenerRegistrationBean bean = new ServletListenerRegistrationBean();bean.setListener(new MyListener());return bean;}
}