2.spring主要的servlet-DispatcherServlet的自动配置

一、使用注解注册原生web组件

1.使用原生servlet

（1）启动类

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

// 扫描servlet，指定原生Servlet组件都放在那里
@ServletComponentScan("com.cxf.servlet")
@SpringBootApplication
public class WebApplicationCxf {

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

（2）自定义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;

// 使用原生servlet API，会直接响应，不会经过spring的拦截器等
@WebServlet(urlPatterns = "/my")
public class MyServlet extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.getWriter().write("66666");
    }
}

2.使用原生filter

import lombok.extern.slf4j.Slf4j;
import javax.servlet.*;
import javax.servlet.annotation.WebFilter;
import java.io.IOException;

@Slf4j
@WebFilter(urlPatterns={"/my","/images/*"}) //拦截的路径
public class MyFilter implements Filter {
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        log.info("MyFilter初始化完成");
    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        log.info("MyFilter工作");
        chain.doFilter(request,response);
    }

    @Override
    public void destroy() {
        log.info("MyFilter销毁");
    }
}

3.使用原生listener

import lombok.extern.slf4j.Slf4j;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import javax.servlet.annotation.WebListener;

// 监听context初始化
@Slf4j
@WebListener
public class MySwervletContextListener implements ServletContextListener {

    @Override
    public void contextInitialized(ServletContextEvent sce) {
        log.info("MySwervletContextListener监听到项目初始化完成");
    }

    @Override
    public void contextDestroyed(ServletContextEvent sce) {
        log.info("MySwervletContextListener监听到项目销毁");
    }
}

二、使用RegistrationBean注册原生web组件

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;

// (proxyBeanMethods = true)：保证依赖的组件始终是单实例的，默认就是true
@Configuration(proxyBeanMethods = true)
public class MyRegistConfig {

    // 注册servlet
    @Bean
    public ServletRegistrationBean myServlet(){
        MyServlet myServlet = new MyServlet();
        // servlet + url映射
        return new ServletRegistrationBean(myServlet,"/my","/my02");
    }

    @Bean
    public FilterRegistrationBean myFilter(){
        MyFilter myFilter = new MyFilter();
//        return new FilterRegistrationBean(myFilter,myServlet());
        FilterRegistrationBean filterRegistrationBean = new FilterRegistrationBean(myFilter);
        filterRegistrationBean.setUrlPatterns(Arrays.asList("/my","/css/*")); // 可以拦截的路径
        return filterRegistrationBean;
    }

    @Bean
    public ServletListenerRegistrationBean myListener(){
        MySwervletContextListener mySwervletContextListener = new MySwervletContextListener();
        return new ServletListenerRegistrationBean(mySwervletContextListener);
    }
}

三、发现一个问题，使用原生的servlet，并不会触发spring的拦截器。

这是为什么呢？

原因：spring默认是注册一个DispatcherServlet，而我们再注册一个原生的servlet，这样容器中就会有两个servlet，而DispatcherServlet匹配的根路径是 / ，原生的servlet匹配的路径是/my，根据最优匹配，请求/my的时候会走原生的servlet，不会走spring的那一套，所以不会触发spring的拦截器，而spring的请求也不会触发原生的拦截器。

四、DispatcherServlet的自动配置

1.springmvc处理逻辑参考博文

springBoot-springMVC请求处理原理_私人博客，有需要请联系17854238061（vx同号）-CSDN博客

2.spring主要的servlet-DispatcherServlet的自动配置

@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE)
@Configuration(proxyBeanMethods = false)
@ConditionalOnWebApplication(type = Type.SERVLET)
@ConditionalOnClass(DispatcherServlet.class)
@AutoConfigureAfter(ServletWebServerFactoryAutoConfiguration.class)
public class DispatcherServletAutoConfiguration {

   /*
    * The bean name for a DispatcherServlet that will be mapped to the root URL "/"
    */
   public static final String DEFAULT_DISPATCHER_SERVLET_BEAN_NAME = "dispatcherServlet";

   /*
    * The bean name for a ServletRegistrationBean for the DispatcherServlet "/"
    */
   public static final String DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME = "dispatcherServletRegistration";

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

      // 注册DispatcherServlet ，id就是dispatcherServlet。属性绑定到 WebMvcProperties；对应的配置文件配置项是 spring.mvc
      @Bean(name = DEFAULT_DISPATCHER_SERVLET_BEAN_NAME)
      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;
      }

      // 注册文件上传解析器
      @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;
      }

   }

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

      // 通过 ServletRegistrationBean<DispatcherServlet> 把 DispatcherServlet 配置进来
      @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()); // 映射的是 / 路径
         registration.setName(DEFAULT_DISPATCHER_SERVLET_BEAN_NAME);
         registration.setLoadOnStartup(webMvcProperties.getServlet().getLoadOnStartup());
         multipartConfig.ifAvailable(registration::setMultipartConfig);
         return registration;
      }

   }
      ……
}