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SpringBoot中注入Servlet&Filter&Listener的应用

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前言:

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1.基本介绍

文档:SpringBoot中注入Servlet&Filter&Listener

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也就是说,SpringBoot开放了和原生WEB组件(Servlet、Filter、Listener)的兼容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

属性名

对应标签

描述

name

<servlet-name>

指定 Servlet 的 name 属性。 如果没有显式指定,则取值为该 Servlet 的完全限定名,即包名+类名

value

<url-pattern>

该属性等价于 urlPatterns 属性,两者不能同时指定。 如果同时指定,通常是忽略 value 的取值

urlPatterns

<url-pattern>

指定一组 Servlet 的 URL 匹配模式

loadOnStartup

<load-on-startup>

指定 Servlet 的加载顺序

initParams

<init-param>

指定一组 Servlet 初始化参数

asyncSupported

<async-supported>

声明 Servlet 是否支持异步操作模式

description

<description>

指定该 Servlet 的描述信息

displayName

<display-name>

指定该 Servlet 的显示名

例子--使用@WebServlet注入Servlet

(1)MyServlet.java

通过继承HttpServlet来开发原生的Servlet使用@WebServlet,表示将其标识的对象注入到Spring容器中urlPatterns = {"servlet01","servlet02"} 对此servlet配置了映射路径对于开发的原生的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:获者,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

属性名

说 明

description

该过滤器的描述信息,等价于 <description>标签。

displayName

该过滤器的显示名,通常配合工具使用,等价于 <display-name> 标签

initParams

指定一组过滤器初始化参数,等价于 <init-param> 标签。

filterName

指定过滤器的 name 属性,等价于 <filter-name>

servletNames

指定过滤器将应用于哪些 Servlet。取值是 @WebServlet 中的 name 属性的取值,或者是 web.xml 中 <servlet-name> 的取值

value/urlPatterns

过滤器的 URL 匹配模式,等价于<url-pattern>标签

dispatcherTypes

指定过滤器的转发模式。具体取值包括: ASYNC、ERROR、FORWARD、INCLUDE、REQUEST。

asyncSupported

声明过滤器是否支持异步操作模式, 等价于<async-supported>标签

例子--使用@WebFilter注入Filter

@WebFilter标识一个过滤器,并注入spring容器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:,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<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;   } }

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