Run Hibernate Schema update from command line

UpdateDDLCreator.kt

package com.bsandhu.server.db

import org.hibernate.boot.MetadataSources
import org.hibernate.boot.model.naming.ImplicitNamingStrategyJpaCompliantImpl
import org.hibernate.boot.registry.BootstrapServiceRegistryBuilder
import org.hibernate.boot.registry.StandardServiceRegistryBuilder
import org.hibernate.boot.spi.MetadataImplementor
import org.hibernate.tool.hbm2ddl.SchemaUpdate


private const val OUT_FILE = "target/schemaUpdate.sql"

class UpdateDDLCreator {

    private val dialect = "org.hibernate.dialect.MySQLDialect"
    private val jdbcUrl = "jdbc:mysql://localhost:3306/mydb"
    private val driver = "com.mysql.jdbc.Driver"

    // Pass these as VM options on the command line
    // -Dusername=xxx -Dpassword=xxx
    private val username = System.getProperty("username")
    private val password = System.getProperty("password")

    /**
     * Compares DB with changes to Java model definition and creates DDL update script
     *
     * https://docs.jboss.org/hibernate/orm/5.0/topical/html/bootstrap/NativeBootstrapping.html
     */
    fun run(){
        
        val props = mapOf(
            "hibernate.dialect" to dialect,
            "hibernate.connection.url" to jdbcUrl,
            "hibernate.connection.username" to username,
            "hibernate.connection.password" to password,
            "hibernate.connection.driver_class" to driver)

        val bsr = BootstrapServiceRegistryBuilder().build()
        val ssrBuilder = StandardServiceRegistryBuilder(bsr)
        ssrBuilder.applySettings(props)
        val registry = ssrBuilder.build()

        val metadata = MetadataSources(registry)
        with (metadata) {
            addAnnotatedClass(UserModel::class.java)
        }

        val metadataBuilder = metadata.metadataBuilder
        metadataBuilder
            .applyImplicitNamingStrategy( ImplicitNamingStrategyJpaCompliantImpl.INSTANCE )
            .build()

        val exporter = SchemaUpdate(metadataBuilder?.build() as MetadataImplementor)
        exporter.setOutputFile(OUT_FILE)

        println("*".repeat(120))
        println("Writing Schema update scripts to $OUT_FILE")
        println("Updated are NOT applied to the DB. These managed via Flyway")
        println("*".repeat(120))
        exporter.execute(true, false)
    }

    companion object {
        @JvmStatic
        fun main(args: Array<String>) {
            UpdateDDLCreator().run()
        }
    }
}