步骤一：修改pox.xml文件



1.首先将 <packaging>jar</packaging>修改为 <packaging>war</packaging>

2.在dependencies里面添加以下代码：

       <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-legacy</artifactId>
        </dependency>

        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>javax.servlet-api</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-test</artifactId>
        </dependency>

	<dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-tomcat</artifactId>
            <scope>provided</scope>
        </dependency>

步骤二：修改SpringBoot中的启动文件

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.builder.SpringApplicationBuilder;
import org.springframework.boot.context.embedded.EmbeddedServletContainerFactory;
import org.springframework.boot.context.embedded.tomcat.TomcatEmbeddedServletContainerFactory;
import org.springframework.boot.web.support.SpringBootServletInitializer;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Import;
import org.springframework.test.context.ActiveProfiles;
@Configuration
@ComponentScan
@EnableAutoConfiguration
@SpringBootApplication
public class DemoApplication extends SpringBootServletInitializer {

    @Override
    protected SpringApplicationBuilder configure(SpringApplicationBuilder application) {
        return application.sources(DemoApplication.class);
    }

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

步骤三：也是最重要的步骤，就是修改完后不要运行该项目，会报错的。
因为这个是为打包而设计的方案，如果大家想要运行项目的话，一定要把spring-boot-starter-tomcat中 <scope>provided</scope>注释掉才可以运行，不然肯定会出错，这点大家一定要注意。
正确的操作步骤应该是在IDEA中找到Build--》Build Artifacts--》点击生成war包，这样利用IDEA将SpringBoot的项目打包成war文件的所有步骤就完成了。