SpringBoot中註入Servlet&Filter&Listener

1.基本介紹

文檔：SpringBoot中註入Servlet&Filter&Listener

1. 考慮到實際開發業務非常複雜和相容問題，SpringBoot支持將Servlet、Filter、Listener註入spring容器中，成為Spring Bean
2. 也就是說，SpringBoot開放了和原生WEB組件（Servlet、Filter、Listener）的相容
3. SpringBoot註入Servlet、Filter、Listener，有兩種方式：
   • 通過註解方式註入
   • 使用RegistrationBean方式註入

2.通過註解方式註入

2.1@WebServlet

例子--使用@WebServlet註入Servlet

（1）MyServlet.java

1. 通過繼承HttpServlet來開發原生的Servlet

2. 使用@WebServlet，表示將其標識的對象註入到Spring容器中

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

4. 對於開發的原生的Servlet，需要使用@ServletComponentScan在SpringBoot主程式中，指定要掃描的原生Servlet，這樣該Servlet才能註入容器

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主程式

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

（3）瀏覽器訪問地址：http://localhost:8080/servlet01獲者 http://localhost:8080/servlet02，返回如下：

註意：註入的Servlet不會被SpringBoot的攔截器攔截（因為原生Servlet和前端控制器DispatcherServlet是統一級別的，而攔截器在DispatcherServlet中）

2.2@WebFilter

例子--使用@WebFilter註入Filter

1. @WebFilter標識一個過濾器，並註入spring容器

2. urlPatterns = {"/css/*", "/images/*"}表示請求/css/目錄或者/images/目錄下的資源時，請求會經過這個過濾器

3. 需要在主程式中，指定要掃描的Filter，這樣該Filter才能註入容器

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
 * 開發Filter並註入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()方法被執行...");
    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        log.info("MyFilter的doFilter()方法被執行...");
        HttpServletRequest httpServletRequest = (HttpServletRequest) request;
        log.info("過濾器處理的uri={}", httpServletRequest.getRequestURI());
        chain.doFilter(request, response);//放行
    }

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

（2）在主程式中配置掃描該過濾器（略）

（3）在瀏覽器訪問地址：http://localhost:8080/images/login.jpg，後臺輸出：

2023-03-23 18:59:36.685  INFO 39228 --- [nio-8080-exec-6] com.li.thymeleaf.filter.MyFilter         : MyFilter的doFilter()方法被執行...
2023-03-23 18:59:36.685  INFO 39228 --- [nio-8080-exec-6] com.li.thymeleaf.filter.MyFilter         : 過濾器處理的uri=/images/login.jpg

有時候後臺沒有輸出，可能是瀏覽器緩存問題

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) {
        //可以加入項目初始化相關的業務
        log.info("MyListener-contextInitialized()-項目初始化OK~");
    }

    @Override
    public void contextDestroyed(ServletContextEvent sce) {
        //可以加入業務
        log.info("MyListener-contextDestroyed()-項目初銷毀...");
    }
}

（2）在主程式 Application.java配置掃描該監聽器

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
 */
//指定掃描監聽器
@ServletComponentScan(basePackages = "com.li.thymeleaf")
@SpringBootApplication
public class Application {
    public static void main(String[] args) {
        ConfigurableApplicationContext ioc =
                SpringApplication.run(Application.class, args);
        //監聽器的contextDestroyed()方法在容器銷毀時觸發
        ioc.stop();
    }
}

（3）啟動項目，控制台輸出：

3.使用RegistrationBean方式註入

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是一個配置類，
 * 預設為單實例模式 proxyBeanMethods=true
 */
@Configuration
public class RegistrationConfig {
    //使用RegistrationBean方式註入Servlet
    @Bean
    public ServletRegistrationBean servlet_() {
        MyServlet myServlet = new MyServlet();
        //將myServlet關聯到ServletRegistrationBean對象
        //可以指定多個映射url
        return new ServletRegistrationBean(myServlet, "/servlet01", "/servlet02");
    }

    //使用RegistrationBean方式註入Filter
    @Bean
    public FilterRegistrationBean filter_() {
        MyFilter myFilter = new MyFilter();//創建原生的Filter對象
        FilterRegistrationBean filterRegistrationBean = new FilterRegistrationBean(myFilter);
        //設置filter的urlPattern
        filterRegistrationBean.setUrlPatterns(Arrays.asList("/css/*", "/images/*"));
        return filterRegistrationBean;
    }

    //使用RegistrationBean方式註入Listener
    @Bean
    public ServletListenerRegistrationBean listener_() {
        MyListener myListener = new MyListener();//創建原生的Listener對象
        return new ServletListenerRegistrationBean(myListener);
    }
}

使用RegistrationBean的方式註入，不必在主程式Application.java中配置掃描

運行程式，可以看到三個組件都被註入到容器中：

4.註意事項和細節

4.1請求自定義Servlet時，為什麼不會到達攔截器？

原因分析：

註入的Servlet會存在Spring容器，DispatcherServlet也存在Spring容器。當多個Servlet都能處理到同一層路徑時，存在精確優先原則/最長首碼匹配原則：**精準匹配 > 目錄匹配 > 擴展名匹配 > /* > / **

如下圖：當瀏覽器請求路徑為/servlet01 時，MyServlet的映射路徑對與瀏覽器請求來說是精準匹配，因此此時MyServlet的映射路徑優先順序高於前端控制器的 /，請求路徑會走tomcat流程，不會到達前端控制器，也就不會執行攔截器。

當然，在SpringBoot中，去調用@Controller目標方法，仍是按照DispatcherServlet分發匹配的機制

4.2DispatcherServlet在SpringBoot如何進行配置和註入

DispatcherServletAutoConfiguration 完成對 DispatcherServlet 的自動配置。

DispatcherServletAutoConfiguration 類，有一個內部類：

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

    @Bean(name = DEFAULT_DISPATCHER_SERVLET_BEAN_NAME)
    //創建了DispatcherServlet對象，併進行一系列設置並返回。
    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;
    }

}

然後通過如下方法，創建DispatcherServletRegistrationBean對象，並將創建的DispatcherServlet對象關聯到這個DispatcherServletRegistrationBean對象中，將DispatcherServletRegistrationBean對象通過@Bean註入到容器中。

@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());//設置路徑 /
      registration.setName(DEFAULT_DISPATCHER_SERVLET_BEAN_NAME);
      registration.setLoadOnStartup(webMvcProperties.getServlet().getLoadOnStartup());
      multipartConfig.ifAvailable(registration::setMultipartConfig);
      return registration;
   }

}