Step 1: Modify pom.xml to increase <packaging>war</packaging>

Step 2: Remove the tomcat component

 <!-- spring boot web -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
            <!--Remove Embedded tomcat Plug-in unit-->
		    <exclusions>
		        <exclusion>
		            <groupId>org.springframework.boot</groupId>
		            <artifactId>spring-boot-starter-tomcat</artifactId>
		        </exclusion> 
		    </exclusions>
        </dependency>

Step 3: Introduce servlet jar, tomcat-related jar

 <!--remove tomcat Plug-ins need to be introduced servlet,tomcat Dependent jar package-->
	<dependency>
	    <groupId>javax.servlet</groupId>
	    <artifactId>javax.servlet-api</artifactId>
	    <version>3.1.0</version>
	    <scope>provided</scope>
	</dependency>
	
	<dependency>
	    <groupId>org.apache.tomcat</groupId>
	    <artifactId>tomcat-servlet-api</artifactId>
	    <version>8.0.36</version>
	    <scope>provided</scope>
	</dependency>

Step 4: Be careful to change the name of the project. FinlName is the name of the project.

 <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
        <finalName>demo</finalName>
    </build>

Step 5: Modify the startup class

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.builder.SpringApplicationBuilder;
import org.springframework.boot.web.support.SpringBootServletInitializer;

@SpringBootApplication //spring boot start
public class StartApp extends SpringBootServletInitializer {
	
	
	 @Override
	    protected SpringApplicationBuilder configure(SpringApplicationBuilder builder) {
	        return builder.sources(StartApp.class);
	    }
		
	public static void main(String[] args) {
		SpringApplication.run(StartApp.class, args);
	}
}

Step 6: Package the mvn clean package into war using the maven command

Then drop war into the webapp directory and start tomcat

Note: Modify your tomcat port number, oh, the port number of the original project configuration file configuration is invalid.

Start tomcat access

Get it done!!!