准备

新建 Spring Starter Project：

在这里插入图片描述

编辑 pom.xml 文件，引入 spring-boot-starter-web 等依赖：


   
   	
    
     4.0.0
        	
    		
     
      org.springframework.boot
     		
     
      spring-boot-starter-parent
     		
     
      2.3.3.RELEASE
     		
      
     	
        	
    
     com.mk
    	
    
     spring-boot-servlet
    	
    
     1.0.0
        	
    
     spring-boot-servlet
        	
    		
     
      1.8
     	
        	
    		
     			
      
       org.springframework.boot
      			
      
       spring-boot-starter-web
      		
     		
     			
      
       org.springframework.boot
      			
      
       spring-boot-devtools
      			
      
       runtime
      			
      
       true
      		
     		
     			
      
       org.springframework.boot
      			
      
       spring-boot-configuration-processor
      			
      
       true
      		
     		
     			
      
       org.projectlombok
      			
      
       lombok
      			
      
       true
      		
     	
    	
    		
     			
      				
       
        org.springframework.boot
       				
       
        spring-boot-maven-plugin
       				
       					
         
          
          
           org.springframework.boot
           
          
           spring-boot-configuration-processor
           
          
          
          
           org.projectlombok
           
          
           lombok

新建一个 Servlet 类：

package com.mk.servlet;import java.io.IOException;import java.io.PrintWriter;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;public class HelloServlet extends HttpServlet {       private static final long serialVersionUID = 1L;        public HelloServlet() {           System.out.println("HelloServlet.HelloServlet()");    }    @Override    public void init() throws ServletException {           System.out.println("HelloServlet.init()");    }        @Override    protected void doGet(HttpServletRequest request, HttpServletResponse response)            throws ServletException, IOException {           System.out.println("HelloServlet.doGet()");                PrintWriter writer = response.getWriter();        writer.write("Hello, " + request.getRemoteAddr());        writer.flush();        writer.close();    }        @Override    public void destroy() {           System.out.println("HelloServlet.destroy()");    }}

新建一个 Servlet 配置类：

package com.mk.configuration;import org.springframework.boot.web.servlet.ServletComponentScan;import org.springframework.context.annotation.Configuration;@Configurationpublic class ServletComponentConfiguration {   }

启动类：

package com.mk;import org.springframework.boot.SpringApplication;import org.springframework.boot.autoconfigure.SpringBootApplication;@SpringBootApplicationpublic class SpringBootServletApplication {   	public static void main(String[] args) {   		SpringApplication.run(SpringBootServletApplication.class, args);	}}

通过使用 Spring Bean 添加 Servlet

编辑 ServletComponentConfiguration 配置类，注册 Servlet 组件（第 16 ~ 24 行）：

package com.mk.configuration;import java.util.Arrays;import javax.servlet.Servlet;import org.springframework.boot.web.servlet.ServletRegistrationBean;import org.springframework.context.annotation.Bean;import org.springframework.context.annotation.Configuration;import com.mk.servlet.HelloServlet;@Configurationpublic class ServletComponentConfiguration {       @Bean    public ServletRegistrationBean
   
     servletRegistration() {           ServletRegistrationBean
    
      registration = new ServletRegistrationBean<>();                registration.setServlet(new HelloServlet());        registration.setUrlMappings(Arrays.asList("/hello"));                return registration;    }}

启动应用，观察控制台输出：

HelloServlet.HelloServlet()

说明 Spring Boot 已经将 HelloServlet 添加到容器中。

访问，看到返回预期的内容，表示 Servlet 组件添加成功：

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注意：第一次访问的过程中，HelloServlet.init() 方法会被调用，此后不再被调用。

通过使用类路劲扫描添加 Servlet

编辑 HelloServlet 类：

使用 @WebServlet 注解，设置 urlPatterns 属性指定 URL 映射路径（第 12 行）

package com.mk.servlet;import java.io.IOException;import java.io.PrintWriter;import javax.servlet.ServletException;import javax.servlet.annotation.WebServlet;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;@WebServlet(urlPatterns = "/hello")public class HelloServlet extends HttpServlet {       // ...略，保持不变}

编辑 ServletComponentConfiguration 配置类：

删除第 10 ~ 18 行

使用 @ServletComponentScan 注解，设置 basePackages 属性指定 Servlet 组件的扫描路径（第 7 行）

package com.mk.configuration;import org.springframework.boot.web.servlet.ServletComponentScan;import org.springframework.context.annotation.Configuration;@Configuration@ServletComponentScan(basePackages = {   "com.mk.servlet"})public class ServletComponentConfiguration {   //    @Bean//    public ServletRegistrationBean
   
     servletRegistration() {   //        ServletRegistrationBean
    
      registration = new ServletRegistrationBean<>();//        //        registration.setServlet(new HelloServlet());//        registration.setUrlMappings(Arrays.asList("/hello"));//        //        return registration;//    }}

启动应用，访问，看到返回预期的内容，表示 Servlet 组件添加成功。