springBoot war package + less detours

I want to create a war package and then run it externally on tomcat for a project written with boot recently.

1. pom add dependencies

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

2. Modify the pom packaging method packaging to war

<groupId>com.lyjn</groupId>
    <artifactId>lyjn-back</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>war</packaging>
    <name>lyjn-back</name>

3. Transform the startup item, inherit SpringBootServletInitializer; rewrite the configure method. Because springboot can recognize its own startup items, but external tomcat does not, so you have to inherit it yourself and read the configuration

@MapperScan("com.lyjn.dao")
@SpringBootApplication
public class LyjnBackApplication extends SpringBootServletInitializer {

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

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

At this point you can use the maven command to package

An error was encountered when it was packaged into a war package and placed in an external tomcat

For versions below tomcat8, put the war package directly in the webapp directory of tomcat, start and check the catania.out log:
**Important: **Start tomcat, you may encounter an error:
Caused by: java.lang.NoClassDefFoundError: javax/el/ELManager
is because: the el-api provided by tomcat conflicts with the el-api. Go to the lib directory of tomcat and overwrite the original jar package. But I did not find el-api.jar

Solution: Directly use tomcat8 version