SpringBoot学习笔记(6)----SpringBoot中使用Servlet,Filter,Listener的三种方式

　　在一般的运用开发中Controller已经大部分都能够实现了，但是也不排除需要自己实现Servlet，Filter,Listener的方式，SpringBoot提供了三种实现方式。

1. 使用Bean的实现方式

首先创建一个Servlet，一个Filter,一个Listener，

DemoServlet.java

　

package com.wangx.boot.util.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 DemoServlet extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("get method");
        doPost(req,resp);
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("post method");
        resp.getWriter().write("hello world");
    }
}

　　DemoFilter.java

package com.wangx.boot.util.filter;


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

public class DemoFilter implements Filter {
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {

    }

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        System.out.println("开始拦截了....");
    }

    @Override
    public void destroy() {

    }
}

DemoListener.java

package com.wangx.boot.util.listener;

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

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

    @Override
    public void contextDestroyed(ServletContextEvent servletContextEvent) {
        System.out.println("contextDestroyed");
    }
}

然后直接在SpringBoot的启动类中将上面几个方法注册为Bean,

SpringBootDemo01Application.java

package com.wangx.boot;

import com.wangx.boot.util.filter.DemoFilter;
import com.wangx.boot.util.listener.DemoListener;
import com.wangx.boot.util.servlet.DemoServlet;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
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;

@SpringBootApplication
public class SpringBootDemo01Application {

    /**
     * 注册Servlet
     * @return
     */
    @Bean
    public ServletRegistrationBean createServlet () {
        //第二个参数为urlPartern
        return new ServletRegistrationBean(new DemoServlet(), "/demoServlet");
    }

    /**
     * 注册Filter
     * @return
     */
    @Bean
    public FilterRegistrationBean createFilter() {
        //第二个参数为需要拦截的路径，不传则拦截所有
        return new FilterRegistrationBean(new DemoFilter(), createServlet());
    }

    /**
     * 注册Listener
     * @return
     */
    @Bean
    public ServletListenerRegistrationBean createrListener() {
        //自定义个Listener.监听整个Context的Servlet
        return new ServletListenerRegistrationBean(new DemoListener());
    }

    public static void main(String[] args) {
        SpringApplication.run(SpringBootDemo01Application.class, args);
    }
}

　　启动项目时会Listener会打印contextInitialized，关闭时会打印contextDestroyed，访问时拦截器打印"开始拦截了...."，并成功访问到Servlet,并输入hello world到浏览器上。

2. 实现ServletContextInitializer接口

　　直接在SpringBoot的启动类中实现ServletContextInitializer，重写onStartup()方法也可以使用Servlet.Filter,Listener，以上面三个Demo类为例，使用ServletContextInitializer的方式的代码：

package com.wangx.boot;

import com.wangx.boot.util.filter.DemoFilter;
import com.wangx.boot.util.listener.DemoListener;
import com.wangx.boot.util.servlet.DemoServlet;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.web.servlet.ServletContextInitializer;

import javax.servlet.DispatcherType;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import java.util.EnumSet;


@SpringBootApplication
public class SpringBootDemo01Application implements ServletContextInitializer {
    public static void main(String[] args) {
        SpringApplication.run(SpringBootDemo01Application.class, args);
    }

    @Override
    public void onStartup(ServletContext servletContext) throws ServletException {
        //创建Servlet,并映射访问路径为demoServlet
        servletContext.addServlet("demoServlet", new DemoServlet()).addMapping("/demoServlet");
        //创建Filter，拦截的Servlet
        servletContext.addFilter("demoFilter", new DemoFilter()).addMappingForServletNames(EnumSet.of(DispatcherType.FORWARD), true, "demoServlet"); //创建Listener servletContext.addListener(new DemoListener()); } }

　　运行结果与1相同

3. 使用注解的方式

　　这是一个SpringBoot官方推荐的方式，也是三种方式中最简单的方式，只需要在SpringBoot的启动类上添加@ServletComponentScan注解，在DemoServlet类上添加@WebServlet(name = "demoServlet", urlPatterns = "/demoServlet")注解，DemoFilter类上添加@WebFilter(urlPatterns = "/*", dispatcherTypes = DispatcherType.FORWARD)（拦截所有请求），DemoListener类上添加@WebListener即可，运行结果与1相同。