Here is a typical build.gradle file created by https://start.spring.io:

buildscript {
	ext {
		springBootVersion = '2.0.0.RELEASE'
	}
	repositories {
		mavenCentral()
		maven { url "https://repo.spring.io/snapshot" }
		maven { url "https://repo.spring.io/milestone" }
	}
	dependencies {
		classpath("org.springframework.boot:spring-boot-gradle-plugin:${springBootVersion}")
	}
}

apply plugin: 'java'
apply plugin: 'eclipse'
apply plugin: 'org.springframework.boot'
apply plugin: 'io.spring.dependency-management'

group = 'com.example'
version = '0.0.1-SNAPSHOT'
sourceCompatibility = 1.8

repositories {
	mavenCentral()
	maven { url "https://repo.spring.io/snapshot" }
	maven { url "https://repo.spring.io/milestone" }
}


ext {
	springStatemachineVersion = '2.0.0.RC1'
}

dependencies {
	compile('org.springframework.statemachine:spring-statemachine-starter')
	testCompile('org.springframework.boot:spring-boot-starter-test')
}

dependencyManagement {
	imports {
		mavenBom "org.springframework.statemachine:spring-statemachine-bom:${springStatemachineVersion}"
	}
}

Having a normal project structure you’d build this with command:

# ./gradlew clean build

Expected Spring Boot packaged fat-jar would be build/libs/demo-0.0.1-SNAPSHOT.jar.