day11-SpringBoot中注入Servlet&Filter&Listener

SpringBoot中注入Servlet&Filter&Listener1.基本介绍

文档：SpringBoot中注入Servlet&Filter&Listener

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

例子–使用@WebServlet注入Servlet

（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")@SpringBootApplicationpublic 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：

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）

2.2@WebFilter

例子–使用@WebFilter注入Filter

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

有时候后台没有输出，可能是浏览器缓存问题

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@WebListenerpublic 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")@SpringBootApplicationpublic 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：

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 */@Configurationpublic 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);    }}

使用RegistrationBean的方式注入，不必在主程序Application.java中配置扫描

运行程序，可以看到三个组件都被注入到容器中：

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。

当然，在SpringBoot中，去调用@Controller目标方法，仍是按照DispatcherServlet分发匹配的机制

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 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;   }}