spring boot的pom.xml修改

<packaging>jar</packaging>
改为
<packaging>war</packaging>

添加
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-tomcat</artifactId>
    <scope>provided</scope><!-- 一定要改为provided  -->
</dependency>

启动类修改为

@SpringBootApplication
public class ApiApplication extends SpringBootServletInitializer{

    @Override
    protected SpringApplicationBuilder configure(SpringApplicationBuilder builder) {
        return super.configure(builder);
    }

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

maven打包

mvn clean package

生成war文件，eg：api-0.0.1-SNAPSHOT

tomcat8，进入Web Application Manager，点击Deploy，选择war文件，完成。