Lesson 5: Scale multi-project builds

Step-by-step instructions

These instructions follow on from what was achieved in the previous lesson.

Add a convention plugin

create a buildSrc directory
in there add a build.gradle.kts build script
add a single plugin
```
plugins {
    `kotlin-dsl`
}
```
configure repositories to include Gradle Plugin Portal
```
repositories {
    gradlePluginPortal()
}
```
in buildSrc add src/main/kotlin directory

add convention plugin script com.tomgregory.maxirail.common-conventions.gradle.kts

plugins {
    java
}

repositories {
    mavenCentral()
}

testing {
    suites {
        named("test", JvmTestSuite::class) {
            useJUnitJupiter()
        }
    }
}

in IntelliJ IDEA’s Gradle Tool Window click Reload All Gradle Projects for IntelliJ IDEA to validate this file
in app’s build script apply the convention plugin by id
```
id("com.tomgregory.maxirail.common-conventions")
```
remove old build script configuration which was extracted into the convention plugin (i.e. java plugin, repositories, and testing blocks)
repeat for service subproject, but leave the java-library plugin
repeat for model subproject, but leave the java-library plugin
run ./gradlew cleanTest test to ensure tests are still passing

Add a version catalog

under gradle directory create file libs.versions.toml
define Spring Boot version using TOML syntax
```
[versions]
spring-boot = "2.6.4"
```

define 3 x Spring Boot dependencies, referencing version defined above

[libraries]
spring-boot-web = { module = "org.springframework.boot:spring-boot-starter-web", version.ref = "spring-boot" }
spring-boot-test = { module = "org.springframework.boot:spring-boot-starter-test", version.ref = "spring-boot" }
spring-boot-starter = { module = "org.springframework.boot:spring-boot-starter", version.ref = "spring-boot" }

define Spring Boot plugin, referencing version defined above

[plugins]
spring-boot = { id = "org.springframework.boot", version.ref = "spring-boot" }

in IntelliJ IDEA’s Gradle Tool Window click Reload All Gradle Projects to make this information available to build scripts

in the build script for app, update dependencies by using the type-safe accessor

dependencies {
    implementation(project(":service"))
    implementation(libs.spring.boot.web)
    testImplementation(libs.spring.boot.test)
}

reference the Spring Boot plugin using the alias defined in the version catalog (IntelliJ IDEA may incorrectly show an error in the editor)
```
alias(libs.plugins.spring.boot)
```

in service’s build script use the type-safe accessor to reference spring-boot-starter

dependencies {
    api(project(":model"))
    implementation(libs.spring.boot.starter)
}

run tests again with ./gradlew test and see that everything is still working

Great! You just used the latest Gradle features to share build logic between multiple subprojects and improve maintainability.

GitHub repository

The gradle-multi-project-masterclass repository contains the final code solution for lessons 2-5.