SpringBoot注册Servlet、Filter、Listener

SpringBoot默认是以jar包的方式启动嵌入式的Servlet容易来启动SpringBoot的Web应用，没有web.xml文件

因此我们可以使用以下方式来注册Servlet、Filter、Listener。

（1）、注册Servlet

package cn.coreqi.servlet;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;

public class MyServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        // 设置响应内容类型
        resp.setContentType("text/html");

        // 实际的逻辑是在这里
        PrintWriter out = resp.getWriter();
        out.println("<h1>MyServlet</h1>");
    }
}

    //注册Servlet
    @Bean
    public ServletRegistrationBean myServlet(){
        ServletRegistrationBean registrationBean = new ServletRegistrationBean(new MyServlet(),"/myservlet");
        return registrationBean;
    }

（2）、注册Filter

package cn.coreqi.filter;

import javax.servlet.*;
import java.io.IOException;
import java.io.PrintWriter;

public class MyFilter implements Filter {
    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        PrintWriter out = servletResponse.getWriter();
        out.println("<h1>MyFilter</h1>");
        filterChain.doFilter(servletRequest,servletResponse);
    }
}

    @Bean
    public FilterRegistrationBean myFilter(){
        FilterRegistrationBean registrationBean = new FilterRegistrationBean();
        registrationBean.setFilter(new MyFilter());
        registrationBean.setUrlPatterns(Arrays.asList("/myservlet"));
        return registrationBean;
    }

（3）、注册Listener

package cn.coreqi.listener;

import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;

public class MyListener implements ServletContextListener {
    @Override
    public void contextInitialized(ServletContextEvent sce) {
        System.out.println("contextInitialized");
    }
}

    @Bean
    public ServletListenerRegistrationBean myListener(){
        ServletListenerRegistrationBean registrationBean = new ServletListenerRegistrationBean();
        registrationBean.setListener(new MyListener());
        return registrationBean;
    }