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day11-SpringBoot中注入Servlet&Filter&Listener

SpringBoot中注入Servlet&Filter&Listener

1.基本介绍

  1. 考虑到实际开发业务非常复杂和兼容问题，SpringBoot支持将Servlet、Filter、Listener注入spring容器中，成为Spring Bean
  2. 也就是说，SpringBoot开放了和原生WEB组件（Servlet、Filter、Listener）的兼容
  3. SpringBoot注入Servlet、Filter、Listener，有两种方式：
    • 通过注解方式注入
    • 使用RegistrationBean方式注入

2.通过注解方式注入

2.1@WebServlet

（1）MyServlet.java

  1. 通过继承HttpServlet来开发原生的Servlet

  2. 使用@WebServlet，表示将其标识的对象注入到Spring容器中

  3. urlPatterns = {"servlet01","servlet02"} 对此servlet配置了映射路径

  4. 对于开发的原生的Servlet，需要使用@ServletComponentScan在SpringBoot主程序中，指定要扫描的原生Servlet，这样该Servlet才能注入容器

package com.li.thymeleaf.servlet;

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

/**
 * @author 李
 * @version 1.0
 */
@WebServlet(urlPatterns = {"/servlet01", "/servlet02"})
public class MyServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.getWriter().write("Hello,MyServlet!");
    }
}

（2）Application.java主程序

package com.li.thymeleaf;

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

/**
 * @author 李
 * @version 1.0
 */
//指定扫描Servlet
@ServletComponentScan(basePackages = "com.li.thymeleaf")
@SpringBootApplication
public class Application {
    public static void main(String[] args) {
        SpringApplication.run(Application.class,args);
    }
}

（3）浏览器访问地址：http://localhost:8080/servlet01获者 http://localhost:8080/servlet02，返回如下：

day11-SpringBoot中注入Servlet&Filter&Listener-LMLPHP

注意：注入的Servlet不会被SpringBoot的拦截器拦截（因为原生Servlet和前端控制器DispatcherServlet是统一级别的，而拦截器在DispatcherServlet中）

day11-SpringBoot中注入Servlet&Filter&Listener-LMLPHP

2.2@WebFilter

  1. @WebFilter标识一个过滤器，并注入spring容器

  2. urlPatterns = {"/css/*", "/images/*"}表示请求/css/目录或者/images/目录下的资源时，请求会经过这个过滤器

  3. 需要在主程序中，指定要扫描的Filter，这样该Filter才能注入容器

package com.li.thymeleaf.filter;

import lombok.extern.slf4j.Slf4j;

import javax.servlet.*;
import javax.servlet.annotation.WebFilter;
import javax.servlet.http.HttpServletRequest;
import java.io.IOException;

/**
 * @author 李
 * @version 1.0
 * 开发Filter并注入spring容器
 */
@Slf4j
@WebFilter(urlPatterns = {"/css/*", "/images/*"})
public class MyFilter implements Filter {
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        log.info("MyFilter的init()方法被执行...");
    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        log.info("MyFilter的doFilter()方法被执行...");
        HttpServletRequest httpServletRequest = (HttpServletRequest) request;
        log.info("过滤器处理的uri={}", httpServletRequest.getRequestURI());
        chain.doFilter(request, response);//放行
    }

    @Override
    public void destroy() {
        log.info("MyFilter的destroy()方法被执行...");
    }
}

（2）在主程序中配置扫描该过滤器（略）

（3）在浏览器访问地址：http://localhost:8080/images/login.jpg，后台输出：

2023-03-23 18:59:36.685  INFO 39228 --- [nio-8080-exec-6] com.li.thymeleaf.filter.MyFilter         : MyFilter的doFilter()方法被执行...
2023-03-23 18:59:36.685  INFO 39228 --- [nio-8080-exec-6] com.li.thymeleaf.filter.MyFilter         : 过滤器处理的uri=/images/login.jpg

2.3@WebListener

（1）MyListener.java

package com.li.thymeleaf.listener;

import lombok.extern.slf4j.Slf4j;

import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import javax.servlet.annotation.WebListener;

/**
 * @author 李
 * @version 1.0
 */
@Slf4j
@WebListener
public class MyListener implements ServletContextListener {
    @Override
    public void contextInitialized(ServletContextEvent sce) {
        //可以加入项目初始化相关的业务
        log.info("MyListener-contextInitialized()-项目初始化OK~");
    }

    @Override
    public void contextDestroyed(ServletContextEvent sce) {
        //可以加入业务
        log.info("MyListener-contextDestroyed()-项目初销毁...");
    }
}

（2）在主程序 Application.java配置扫描该监听器

package com.li.thymeleaf;

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

/**
 * @author 李
 * @version 1.0
 */
//指定扫描监听器
@ServletComponentScan(basePackages = "com.li.thymeleaf")
@SpringBootApplication
public class Application {
    public static void main(String[] args) {
        ConfigurableApplicationContext ioc =
                SpringApplication.run(Application.class, args);
        //监听器的contextDestroyed()方法在容器销毁时触发
        ioc.stop();
    }
}

（3）启动项目，控制台输出：

day11-SpringBoot中注入Servlet&Filter&Listener-LMLPHP

3.使用RegistrationBean方式注入

RegistrationConfig.java：

package com.li.thymeleaf.config;

import com.li.thymeleaf.filter.MyFilter;
import com.li.thymeleaf.listener.MyListener;
import com.li.thymeleaf.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;

/**
 * @author 李
 * @version 1.0
 * RegistrationConfig是一个配置类，
 * 默认为单实例模式 proxyBeanMethods=true
 */
@Configuration
public class RegistrationConfig {
    //使用RegistrationBean方式注入Servlet
    @Bean
    public ServletRegistrationBean servlet_() {
        MyServlet myServlet = new MyServlet();
        //将myServlet关联到ServletRegistrationBean对象
        //可以指定多个映射url
        return new ServletRegistrationBean(myServlet, "/servlet01", "/servlet02");
    }

    //使用RegistrationBean方式注入Filter
    @Bean
    public FilterRegistrationBean filter_() {
        MyFilter myFilter = new MyFilter();//创建原生的Filter对象
        FilterRegistrationBean filterRegistrationBean = new FilterRegistrationBean(myFilter);
        //设置filter的urlPattern
        filterRegistrationBean.setUrlPatterns(Arrays.asList("/css/*", "/images/*"));
        return filterRegistrationBean;
    }

    //使用RegistrationBean方式注入Listener
    @Bean
    public ServletListenerRegistrationBean listener_() {
        MyListener myListener = new MyListener();//创建原生的Listener对象
        return new ServletListenerRegistrationBean(myListener);
    }
}

运行程序，可以看到三个组件都被注入到容器中：

day11-SpringBoot中注入Servlet&Filter&Listener-LMLPHP

4.注意事项和细节

4.1请求自定义Servlet时，为什么不会到达拦截器？

原因分析：

注入的Servlet会存在Spring容器，DispatcherServlet也存在Spring容器。当多个Servlet都能处理到同一层路径时，存在精确优先原则/最长前缀匹配原则：**精准匹配 > 目录匹配 > 扩展名匹配 > /* > / **

如下图：当浏览器请求路径为/servlet01 时，MyServlet的映射路径对与浏览器请求来说是精准匹配，因此此时MyServlet的映射路径优先级高于前端控制器的 /，请求路径会走tomcat流程，不会到达前端控制器，也就不会执行拦截器。

day11-SpringBoot中注入Servlet&Filter&Listener-LMLPHP

4.2DispatcherServlet在SpringBoot如何进行配置和注入

DispatcherServletAutoConfiguration 完成对 DispatcherServlet 的自动配置。

DispatcherServletAutoConfiguration 类，有一个内部类：

@Configuration(proxyBeanMethods = false)
@Conditional(DefaultDispatcherServletCondition.class)
@ConditionalOnClass(ServletRegistration.class)
@EnableConfigurationProperties(WebMvcProperties.class)
protected static class DispatcherServletConfiguration {

    @Bean(name = DEFAULT_DISPATCHER_SERVLET_BEAN_NAME)
    //创建了DispatcherServlet对象，并进行一系列设置并返回。
    public DispatcherServlet dispatcherServlet(WebMvcProperties webMvcProperties) {
        DispatcherServlet dispatcherServlet = new DispatcherServlet();
        dispatcherServlet.setDispatchOptionsRequest(webMvcProperties.isDispatchOptionsRequest());
        dispatcherServlet.setDispatchTraceRequest(webMvcProperties.isDispatchTraceRequest());
        dispatcherServlet.setThrowExceptionIfNoHandlerFound(webMvcProperties.isThrowExceptionIfNoHandlerFound());
        dispatcherServlet.setPublishEvents(webMvcProperties.isPublishRequestHandledEvents());
        dispatcherServlet.setEnableLoggingRequestDetails(webMvcProperties.isLogRequestDetails());
        return dispatcherServlet;
    }

    @Bean
    @ConditionalOnBean(MultipartResolver.class)
    @ConditionalOnMissingBean(name = DispatcherServlet.MULTIPART_RESOLVER_BEAN_NAME)
    public MultipartResolver multipartResolver(MultipartResolver resolver) {
        // Detect if the user has created a MultipartResolver but named it incorrectly
        return resolver;
    }

}

然后通过如下方法，创建DispatcherServletRegistrationBean对象，并将创建的DispatcherServlet对象关联到这个DispatcherServletRegistrationBean对象中，将DispatcherServletRegistrationBean对象通过@Bean注入到容器中。

@Configuration(proxyBeanMethods = false)
@Conditional(DispatcherServletRegistrationCondition.class)
@ConditionalOnClass(ServletRegistration.class)
@EnableConfigurationProperties(WebMvcProperties.class)
@Import(DispatcherServletConfiguration.class)
protected static class DispatcherServletRegistrationConfiguration {

   @Bean(name = DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME)
   @ConditionalOnBean(value = DispatcherServlet.class, name = DEFAULT_DISPATCHER_SERVLET_BEAN_NAME)
   public DispatcherServletRegistrationBean dispatcherServletRegistration(DispatcherServlet dispatcherServlet,
         WebMvcProperties webMvcProperties, ObjectProvider<MultipartConfigElement> multipartConfig) {
      DispatcherServletRegistrationBean registration = new DispatcherServletRegistrationBean(dispatcherServlet,
            webMvcProperties.getServlet().getPath());//设置路径 /
      registration.setName(DEFAULT_DISPATCHER_SERVLET_BEAN_NAME);
      registration.setLoadOnStartup(webMvcProperties.getServlet().getLoadOnStartup());
      multipartConfig.ifAvailable(registration::setMultipartConfig);
      return registration;
   }

}
day11-SpringBoot中注入Servlet&amp;Filter&amp;Listener-LMLPHP
03-23 21:32
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