How to avoid repeating dependency versions in a multi-module Gradle project? - spring

Question

There's a sample Spring Boot project here that contains two modules.
The build.gradle for one of the modules looks like this:
buildscript {
ext { springBootVersion = '2.1.4.RELEASE' }
repositories { mavenCentral() }
dependencies { classpath("org.springframework.boot:spring-boot-gradle-plugin:${springBootVersion}") }
}
plugins {
id "io.spring.dependency-management" version "1.0.5.RELEASE"
}
apply plugin: 'java'
apply plugin: 'eclipse'
apply plugin: 'org.springframework.boot'
apply plugin: 'io.spring.dependency-management'
bootJar {
baseName = 'gs-multi-module-application'
version = '0.0.1-SNAPSHOT'
}
sourceCompatibility = 1.8
repositories { mavenCentral() }
dependencies {
compile('org.springframework.boot:spring-boot-starter-actuator')
compile('org.springframework.boot:spring-boot-starter-web')
compile project(':library')
testCompile('org.springframework.boot:spring-boot-starter-test')
}
The other module's build.gradle looks like this:
buildscript {
repositories { mavenCentral() }
}
plugins { id "io.spring.dependency-management" version "1.0.5.RELEASE" }
ext { springBootVersion = '2.1.4.RELEASE' }
apply plugin: 'java'
apply plugin: 'eclipse'
jar {
baseName = 'gs-multi-module-library'
version = '0.0.1-SNAPSHOT'
}
sourceCompatibility = 1.8
repositories { mavenCentral() }
dependencies {
compile('org.springframework.boot:spring-boot-starter')
testCompile('org.springframework.boot:spring-boot-starter-test')
}
dependencyManagement {
imports { mavenBom("org.springframework.boot:spring-boot-dependencies:${springBootVersion}") }
}
The springBootVersion = '2.1.4.RELEASE' is declared in both modules. For a 2 module project that might not be a problem, but if my project had 10 modules and I wanted to make sure that all modules always depend on the same version of Spring Boot, it would be inconvenient and error-prone to repeat this version in every module.
Similarly, I might want to add a dependency on commons-io to both of these modules, and ensure they both always depend on the same version of commons-io.
How can I avoid repeating the version numbers in each and every build.gradle file?

Answer 1

See this Gradle documentation : a good practice in Gradle is to configure subprojects which share common traits in a single place, for example in the root project's build script (or using custom plugins)
EDIT the solution proposed here is no longer considered as good practice from Gradle team (the link above does not even mention subproject bloc in latests Gradle version doc); thank you #buggy for the warning .
In your example taken from Spring boot documentation, this pattern could be applied to centralize Spring boot and other common dependencies versions in a single place, but you could go further and also configure other common traits (Java plugin configuration, repositoties, etc..)
Here is how I would re-write the Spring example to make it cleaner and DRY:
Root project
/**
* Add Springboot plugin into build script classpath (without applying it)
* This is this only place where you need to define the Springboot version.
*
* See https://docs.spring.io/spring-boot/docs/current/gradle-plugin/reference/html/#managing-dependencies-using-in-isolation
*/
plugins {
id "org.springframework.boot" version "2.1.4.RELEASE" apply false
}
// Set version for dependencies share between subprojects
ext {
commonsIoVersion = "2.6"
}
subprojects {
// common config for all Java subprojects
apply plugin: "java"
apply plugin: "eclipse"
sourceCompatibility = 1.8
repositories {
mavenCentral()
}
// apply Spring Boot's dependency management plugin
apply plugin: "io.spring.dependency-management"
}
Library sub-project
// no need for additional plugins
jar {
baseName = 'gs-multi-module-library'
version = '0.0.1-SNAPSHOT'
}
dependencies {
implementation('org.springframework.boot:spring-boot-starter')
implementation "commons-io:commons-io:${commonsIoVersion}"
testCompile('org.springframework.boot:spring-boot-starter-test')
}
dependencyManagement {
imports {
mavenBom org.springframework.boot.gradle.plugin.SpringBootPlugin.BOM_COORDINATES
}
}
Application sub-project
plugins {
id "org.springframework.boot"
}
bootJar {
baseName = 'gs-multi-module-application'
version = '0.0.1-SNAPSHOT'
}
dependencies {
implementation project(':library')
implementation ('org.springframework.boot:spring-boot-starter-actuator')
implementation ('org.springframework.boot:spring-boot-starter-web')
implementation "commons-io:commons-io:${commonsIoVersion}"
// could also be configured in root project.
testCompile('org.springframework.boot:spring-boot-starter-test')
}
Notes
this solution uses the new plugins {} DSL only (no need for old buildscript block)
version of the io.spring.dependency-management should not be configured explicitly, it will be inherit from Spring boot plugin

Answer 2

You can move the ext{} block to a new file and reference it in your project's build.gradle file via the apply from: statement.
// project/versions.gradle
ext {
springBootVersion = '2.1.4.RELEASE'
}
// project/build.gradle
buildscript {
apply from: 'versions.gradle'
}
// module/build.gradle
dependencies {
implementation "some.dependency:dependency:$springBootVersion"
}
Now you only have to define your dependency versions in one place.
Typically, a project will have a project-level build.gradle file in addition to module-specific build.gradle files. However, the repo you shared is missing the project-level build script. This is why the ext{} block is defined in each module's build script. This is likely not optimal, and I recommend looking at other repos to see how different developers tackled this issue.

Answer 3

There's a Gradle consistent versions plugin that will handle this:
https://github.com/palantir/gradle-consistent-versions
After you set this plugin up in the root build.gradle file, you will create a versions.props file like this, to use the example from the documentation.
com.fasterxml.jackson.*:jackson-* = 2.9.6
com.google.guava:guava = 21.0
com.squareup.okhttp3:okhttp = 3.12.0
junit:junit = 4.12
org.assertj:* = 3.10.0
There's also a versions.locks file, which is auto-generated by ./gradlew --write-locks. You can then specify version-less dependencies in your build.gradle files.