0017SpringBoot注册Servlet三大组件（Servlet、Filter、Listener）

由于SpringBoot默认是以jar包的形式启动嵌入式servlet容器来启动SpringBoot的web应用，所以没有web.xml文件，那么如何配置Servlet、Filter、Listener呢？

1、自定义Servlet、Filter、Listener容器

2、将各自对应的ServletRegistrationBean、FilterRegistrationBean、ServletListenerRegistrationBean以组件的形式加入到容器中

具体实现如下：

a、自定义servlert类

package com.myself.servlet;

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

public class MyServlet extends HttpServlet{
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doPost(req,resp);
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.getWriter().write("hello MyServlet");
    }
}

b、自定义filter类

package com.myself.filter;

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

public class MyFilter implements Filter {
    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        System.out.println("MyFilter process...");
        chain.doFilter(request,response);
    }

}

c、自定义listener类

package com.myself.listener;

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

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

    @Override
    public void contextDestroyed(ServletContextEvent sce) {
        System.out.println("contextDestroyed...当前web项目销毁");
    }
}

d、将对应的注册类以组件的形式加入到容器中

package com.myself.config;

import com.myself.filter.MyFilter;
import com.myself.listener.MyListener;
import com.myself.servlet.MyServlet;
import org.springframework.boot.web.servlet.FilterRegistrationBean;
import org.springframework.boot.web.servlet.ServletListenerRegistrationBean;
import org.springframework.boot.web.servlet.ServletRegistrationBean;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

import java.util.Arrays;

@Configuration
public class MyServerConfig {
    @Bean
    public ServletRegistrationBean myServlet(){
        ServletRegistrationBean<MyServlet> myServletServletRegistrationBean = new ServletRegistrationBean<>();
        myServletServletRegistrationBean.setServlet(new MyServlet());
        myServletServletRegistrationBean.setUrlMappings(Arrays.asList("/myServlet"));
        myServletServletRegistrationBean.setLoadOnStartup(1);
        return myServletServletRegistrationBean;
    }

    @Bean
    public FilterRegistrationBean myFilter(){
        FilterRegistrationBean<MyFilter> myFilterFilterRegistrationBean = new FilterRegistrationBean<>();
        myFilterFilterRegistrationBean.setFilter(new MyFilter());
        myFilterFilterRegistrationBean.setUrlPatterns(Arrays.asList("/hello","/myFilter"));
        return myFilterFilterRegistrationBean;
    }

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

若有理解不到之处，望指正。