Listener

作用：监听某个事件的发生，状态的改变
内部机制：接口回调

八个Web监听器

接口名	作用
ServletContextListener	ServletContext对象的创建
HttpSessionListener	Session对象的创建
ServletRequestListener	Request对象的创建
ServletContextAttributeListener	ServletContext属性变化
HttpSessionAttributeListener	Session属性变化
ServletRequestAttributeListener	Request属性变化
HttpSessionActivationListener	Session钝化与活化
HttpSessionBindingListener	Session与对象的绑定

注册Listener

父pom文件

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
<!--        <version>3.1.2</version>-->
        <version>2.2.5.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.chensir</groupId>
    <artifactId>springboot</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>springboot</name>
    <description>springboot</description>
    <properties>
        <java.version>8</java.version>
    </properties>

    <packaging>pom</packaging>

    <modules>
        <module>servlet</module>
    </modules>

    <dependencies>
        <dependency>
            <groupId>cn.hutool</groupId>
            <artifactId>hutool-all</artifactId>
            <version>5.8.3</version>
        </dependency>

<!--        <dependency>-->
<!--            <groupId>org.slf4j</groupId>-->
<!--            <artifactId>slf4j-log4j12</artifactId>-->
<!--            <version>1.7.25</version>-->
<!--        </dependency>-->

        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <version>1.18.22</version>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>

pom文件

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>com.chensir</groupId>
        <artifactId>springboot</artifactId>
        <version>0.0.1-SNAPSHOT</version>
        <relativePath>../pom.xml</relativePath>
    </parent>

    <artifactId>servlet</artifactId>

    <dependencies>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>

使用注解方式

使用注解在启动类上必须加 @ServletComponentScan注解，若使用bean方式注册，则不需要

ServletListener

package com.chensir.javaWeb;

import cn.hutool.core.date.StopWatch;
import lombok.extern.slf4j.Slf4j;

import javax.servlet.ServletRequestEvent;
import javax.servlet.ServletRequestListener;
import javax.servlet.annotation.WebListener;

@WebListener
@Slf4j
public class ServletListener implements ServletRequestListener {

    // StopWatch存储一组任务耗时时间
    StopWatch stopWatch = null;

    @Override
    public void requestInitialized(ServletRequestEvent sre) {
        stopWatch = new StopWatch("监控");
        stopWatch.start();
        log.info("-------有人来了----------");
    }

    @Override
    public void requestDestroyed(ServletRequestEvent sre){
        stopWatch.stop();
        log.info("-------有人出来了,耗时：{}----------",stopWatch.getTotalTimeSeconds());

        // todo:如果超过多少时间，发信息给开发者
    }
}

HelloServlet

package com.chensir.javaWeb;

import cn.hutool.core.thread.ThreadUtil;
import lombok.extern.slf4j.Slf4j;

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

@WebServlet(value = {"/hello"})
@Slf4j
public class HelloServlet extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws IOException {
        resp.setContentType("text/html;charset=utf-8");
        resp.getWriter().write("你好,宝宝");

        log.info("给航天员打招呼！");

        // 睡眠5s
        ThreadUtil.safeSleep(5000);
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) {
    }
}

启动类

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.web.servlet.ServletComponentScan;

@SpringBootApplication
@ServletComponentScan
public class ServletApplication {

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

}

通过RegistrationBean注册

ServletListener

HelloServlet

MyWebConfig

import com.chensir.javaWeb.HelloServlet;
import com.chensir.javaWeb.ServletListener;
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;

@Configuration
public class MyWebConfig {

    @Bean
    public ServletRegistrationBean servletRegistrationBean() {
        ServletRegistrationBean servletRegistrationBean = new ServletRegistrationBean();
        servletRegistrationBean.setServlet(new HelloServlet());
        servletRegistrationBean.addUrlMappings("/helloBaby");
        return servletRegistrationBean;
    }

    @Bean
    public ServletListenerRegistrationBean servletListenerRegistrationBean() {
        ServletListenerRegistrationBean bean = new ServletListenerRegistrationBean();
        bean.setListener(new ServletListener());
        // 启用
        bean.setEnabled(true);
        return bean;
    }
}