Writing a Gradle Build Script for a Spring Boot Project

Setting up Gradle for a Spring Boot project requires two plugins working together, and a common mistake on either one causes subtle failures that are not obvious from the error messages.

The two required plugins

• org.springframework.boot provides bootJar for packaging an executable fat JAR and bootRun for local development; without it you get a standard JAR that does not include Spring Boot's launcher
• io.spring.dependency-management imports the Spring Boot BOM, letting you declare spring-boot-starter-web without any version number — the BOM ensures all transitive versions are compatible; skipping this plugin means you must version every dependency manually and risk subtle mismatches
• Skipping the dependency management plugin is the most common setup mistake — Jackson and Spring Web can silently use mismatched versions, causing serialization failures that only appear at runtime

Dependency configuration

• Use implementation for application dependencies — it keeps them internal to the module and avoids leaking transitive dependencies to consumers
• Use testImplementation for JUnit, Mockito, AssertJ — they belong only on the test classpath and should never ship in the packaged artifact
• compileOnly for Lombok — needed at compile time for annotation processing, not at runtime; the Kotlin equivalent is kapt

Docker-optimized JAR

• Enable layered bootJar with bootJar { layered { enabled = true } } — Spring Boot splits the JAR into dependency layer, Spring Boot loader layer, and application class layer; Docker caches the stable layers and only rebuilds the application layer on code changes
• Use the Kotlin DSL for new projects — build.gradle.kts provides compile-time type safety and IDE autocomplete in the build script, catching configuration errors before the build runs