Grails normally will run any *Bootstrap classes at startup. A Bootstrap class has an init and destroy closure. The init closure is invoked during startup and destroy when the application stops. The class name must end with Bootstrap and be placed in the grails-app/init folder. Ever since Grails 3.2, we can skip the execution of Bootstrap classes by setting the Java system property grails.bootstrap.skip with the value true.

In the following example Bootstrap class, we simply add a println to see the effect of using the system property grails.bootstrap.skip:

// File: grails-app/init/mrhaki/Bootstrap.groovy
package mrhaki

class Bootstrap {
    def init = { servletContext ->
        println "Run Bootstrap"
    }

    def destroy = {
    }
}

First, we build the application, and then start it from the generated WAR file:

$ gradle build
...
:build

BUILD SUCCESSFUL

Total time: 22.235 secs
$ java -jar build/libs/sample-app-0.1.war
Run Bootstrap
Grails application running at http://localhost:8080 in environment: production

Next, we use the Java system property grails.bootstrap.skip:

$ java -Dgrails.bootstrap.skip=true -jar build/libs/sample-app-0.1.war

Notice the println statement from Bootstrap.groovy is not invoked anymore.