Dompting the Elephant: Making Sense of Gradle for Android Developers

In this talk, we’ll demystify how Gradle works under the hood. You’ll gain a clear mental model of the build lifecycle, understand the difference between configuration and execution phases, and learn how tasks, plugins, and dependencies interact.

1. Dompting the Elephant: Making Sense of Gradle for Android Developers Yves Kalume
2. GDE & Android Developer at Moneco Yves Kalume @kalumeyves
4. Gradle in a nutshell A powerful and fl exible task runner
5. Gradle Build What you are trying to build build.gradle(.kts) Project Tasks Properties : Build script
6. Gradle Build Settings Project build.gradle(.kts) settings.gradle(.kts) include(“:project”) Droid rootProject.name = “Droid” gradle.properties ./gradlew <task> -P <option>
7. Project public interface Project extends Comparable<Project> { String DEFAULT_BUILD_FILE = "build.gradle"; String DEFAULT_BUILD_DIR_NAME = "build"; String GRADLE_PROPERTIES = "gradle.properties"; File getProjectDir(); File getBuildDir(); void apply(Map<String, ?> options); void afterEvaluate(Action<? super Project> action); void dependencies(Action<? super DependencyHandler> action); void repositories(Action<? super RepositoryHandler> action); Task task(String name); ... }
8. Build phases
9. Initialization (Build phases) • Create a settings instance and evaluate settings.gradle(.kts) • Determine which project are included and create their instances
10. Con fi guration (Build phases) • Reads each build.gradle • Con fi gures a Project instance for every module
11. Con fi guration (Build phases) processTestResources Build assemble jar check classes compileJava processResources test testClasses compileTestJava DAG (Directed Acyclic Graph) dependsOn dependsOn
12. Execution (Build phases) Schedules and executes the selected tasks
13. This page is Intentionally left blank
14. Plugin android { compileSdk = 34 defaultConfig { applicationId = "ke.droidcon.app" } }
15. Plugin android { compileSdk = 34 defaultConfig { applicationId = "ke.droidcon.app" } } plugins { id("com.android.application") id("org.jetbrains.kotlin.android") }
16. Plugin abstract class SamplePlugin : Plugin<Project> { override fun apply(project: Project) { project.tasks.register("MyCustomTask") { doLast { println("Hello world from the build file!") } } } }
17. Binary plugin • Implemented in a compiled language (.kt fi le) • Is packaged as a JAR fi le
18. Binary plugin MyProject ├── app │ └── src └── settings.gradle.kts
19. Binary plugin MyProject ├── my-plugin │ ├── themodule │ │ ├── src │ │ └── build.gradle.kts │ └── settings.gradle.kts ├── app │ └── src └── settings.gradle.kts
20. Binary plugin plugins { `kotlin-dsl` } gradlePlugin { plugins { create("droidconke") { id = "ke.droidcon.greeting" implementationClass = "ke.droidcon.GreetingPlugin" } } } MyProject/my-plugin/build.gradle.kts
21. abstract class GreetingTask : DefaultTask() { @Input var name = "Droidcon" @OutputFile val myFile: File = File(name) @TaskAction fun action() { println("Hello $name Karibu droidcon") myFile.createNewFile() myFile.writeText(fileText.get()) } } MyProject/my-plugin/src/main/kotlin/…
22. abstract class SamplePlugin : Plugin<Project> { override fun apply(project: Project) { project.tasks.register<GreetingTask>("greet") { name = "Kalume" } } } MyProject/my-plugin/src/main/kotlin/…
23. abstract class SamplePlugin : Plugin<Project> { override fun apply(project: Project) { project.tasks.register<GreetingTask>("greet") { name = "Kalume" } } } MyProject/my-plugin/src/main/kotlin/…
24. interface GreetingPluginExtension { val name: Property<String> } MyProject/my-plugin/src/main/kotlin/…
25. abstract class SamplePlugin : Plugin<Project> { override fun apply(project: Project) { val extension = project.extensions.create<GreetingPluginExtension>("greetingConfig") project.tasks.register<GreetingTask>("greet") { name = extension.name.get() } } } MyProject/my-plugin/src/main/kotlin/…
26. pluginManagement { includeBuild(“my-plugin”) repositories { google() gradlePluginPortal() mavenCentral() } } MyProject/settings.gradle.kts
27. plugin { id("ke.droidcon.greeting") } MyProject/app/build.gradle.kts
28. plugin { id("ke.droidcon.greeting") } greetingConfig { name = "Kalume" } ./gradlew greet MyProject/app/build.gradle.kts
29. Dependency Resolution
30. Dependency Resolution Two phases Graph resolution Artifact resolution
31. implementation("org.jetbrains.kotlinx:kotlinx-serialization-json:1.7.1")
32. Graph resolution phase • Gradle looks at all the declared dependencies • Transitive dependencies • Constructs a resolved dependency graph
33. Component A speci fi c version of a library kotlinx-serialization-json:1.7.1 kotlinx-serialization-json:1.6.0 Metadata what to know about that component. a .pom or .ivy fi le component’s dependencies available variants Attributes key-value pairs that describe characteristics of a variant E.g : org.gradle.jvm.version=17 Variants Each variant is designed for a di ff erent target platform or usage scenario. E.g : JVM, Kotlin/Native, JS or the context it’s being used in
34. How gradle build the Dependency Graph My App Library A Library C
35. How gradle build the Dependency Graph My App Library A 1.3.2 Library C 1.0.2 Library B 1.2.3 Library C 2.0.4 My App Library A 1.3.2 Library B 1.2.3 Library C 2.0.4
36. ./gradlew dependencies compileClasspath - Compile classpath for 'main'. + --- org.jetbrains.kotlin:kotlin-stdlib:2.2.10 | \ --- org.jetbrains:annotations:13.0 \ --- org.jetbrains.kotlinx:kotlinx-serialization-json:1.9.0 \ --- org.jetbrains.kotlinx:kotlinx-serialization-json-jvm:1.9.0 + --- org.jetbrains.kotlinx:kotlinx-serialization-bom:1.9.0 | + --- org.jetbrains.kotlinx:kotlinx-serialization-core:1.9.0 (c) | + --- org.jetbrains.kotlinx:kotlinx-serialization-json-jvm:1.9.0 (c) | + --- org.jetbrains.kotlinx:kotlinx-serialization-json:1.9.0 (c) | \ --- org.jetbrains.kotlinx:kotlinx-serialization-core-jvm:1.9.0 (c) + --- org.jetbrains.kotlin:kotlin-stdlib:2.2.0 -> 2.2.10 (*) \ --- org.jetbrains.kotlinx:kotlinx-serialization-core:1.9.0 \ --- org.jetbrains.kotlinx:kotlinx-serialization-core-jvm:1.9.0 + --- org.jetbrains.kotlinx:kotlinx-serialization-bom:1.9.0(*) \ --- org.jetbrains.kotlin:kotlin-stdlib:2.2.0 -> 2.2.10 (*)
37. ./gradlew dependencies compileClasspath - Compile classpath for 'main'. + --- org.jetbrains.kotlin:kotlin-stdlib:2.2.10 | \ --- org.jetbrains:annotations:13.0 \ --- org.jetbrains.kotlinx:kotlinx-serialization-json:1.9.0 \ --- org.jetbrains.kotlinx:kotlinx-serialization-json-jvm:1.9.0 + --- org.jetbrains.kotlinx:kotlinx-serialization-bom:1.9.0 | + --- org.jetbrains.kotlinx:kotlinx-serialization-core:1.9.0 (c) | + --- org.jetbrains.kotlinx:kotlinx-serialization-json-jvm:1.9.0 (c) | + --- org.jetbrains.kotlinx:kotlinx-serialization-json:1.9.0 (c) | \ --- org.jetbrains.kotlinx:kotlinx-serialization-core-jvm:1.9.0 (c) + --- org.jetbrains.kotlin:kotlin-stdlib:2.2.0 -> 2.2.10 (*) \ --- org.jetbrains.kotlinx:kotlinx-serialization-core:1.9.0 \ --- org.jetbrains.kotlinx:kotlinx-serialization-core-jvm:1.9.0 + --- org.jetbrains.kotlinx:kotlinx-serialization-bom:1.9.0(*) \ --- org.jetbrains.kotlin:kotlin-stdlib:2.2.0 -> 2.2.10 (*)
38. Artifact Resolution Gradle : “Alright, I know what I need; now let’s go and get it.” • Contacts the repositories you’ve declared dependencyResolutionManagement { repositoriesMode.set(RepositoriesMode.FAIL_ON_PROJECT_REPOS) repositories { google() mavenCentral() maven { url = uri("https: // yveskalume.dev") } } }
39. Artifact Resolution Gradle : “Alright, I know what I need; now let’s go and get it.” • Downloads these fi les into its local cache • Contacts the repositories you’ve declared
40. Deamon
41. Deamon • A long-lived background process • Executes your builds much more quickly • Avoid the expensive bootstrapping process • Leverage caching, by keeping data about your project in memory.
42. ./path/to/local/distribution/bin/gradle <SomeTask>
43. ./path/to/local/distribution/bin/gradle exec "$JAVACMD" "$@" Gradle Client JVM Gradle Daemon Create Find or create
44. ./path/to/local/distribution/bin/gradle <SomeTask> Gradle Client JVM Gradle Daemon Forward inputs Input (command line args,…) Run the builds Outputs
45. ./path/to/local/distribution/bin/gradle <SomeTask> Gradle Client JVM Gradle Daemon Keep running Exit
46. org.gradle.launcher.GradleMain
47. Gradle Wrapper is the recommended
48. ./gradlew <SomeTask>
49. gradlew • Starts a tiny JVM using gradle/wrapper/gradle-wrapper.jar • That JVM locates or downloads Gradle from gradle/wrapper/gradle- wrapper.properties • Uses Java re fl ection to start Gradle itself inside the same process • That tiny JVM essentially becomes the Gradle Client JVM
50. org.gradle.wrapper.GradleWrapperMain
51. What Can Go Wrong with the Gradle Daemon • Memory leaks or corruption of global state • Builds that don’t release resources properly Solution • Kill the process manually • --no-daemon fl ag
52. --no-daemon • The client JVM may convert itself into a daemon JVM (if it is compatible with build requirements) • The build happens inside the single JVM • If not compatible a new disposable JVM will still be started for the build and exit at the end of the build
53. • It’s detecting more than one Java version in your environment. • Your Gradle JDK and your system JAVA_HOME point to di ff erent Java installations • Not dangerous, but it increases memory usage unnecessarily • Just make sure your Gradle JDK matches the JAVA_HOME “Multiple Gradle daemons might be spawned because the Gradle JDK and JAVA_HOME locations are di ff erent.”
54. Caching
55. Remember about Tasks ? A task can actually be seen like a pure function. Action Input Output
56. Remember about Tasks ? A task can actually be seen like a pure function. It can be can be deterministic Task 1 Input Output Task 2 Etc
57. Gradle cache Local cache Remote cache In-memory (Deamon) in-project Out of the project Remote Build cache Proxy Con fi guration cache Build folder Dependency cache Build cache
58. Con fi guration-cache • org.gradle.configuration-cache=true • org.gradle.configuration-cache.problems=warn
59. Build folder • Execution phase • Analyze input and compare with the most recent run • {project}/.gradle/version/executionHistory/ executionHistory.bin • Checks your module’s build/ folder and reuses those results • ./gradlew clean
60. Dependency cache • ~/.gradle/caches/modules-2 • Stores jars, aars, and poms fi les • Using a proxy for Maven repositories can be a good idea
62. Build cache • Reuse task outputs from any earlier build in any location on the local machine • ~/.gradle/caches/build-cache-1 • org.gradle.caching=true
63. Build cache
64. Build cache key Cache Key Source files -> Hash Compiler args -> Hash Java version -> Hash ~/.gradle/caches/build-cache-1
65. Gradle caching Module build folder Task Input Task Task Output UP-TO-DATE
66. Gradle caching Module build folder Task Input Task Build cache Task Output FROM CACHE
67. Gradle caching Module build folder Task Input Task Task Action Dorg.gradle.caching.debug=true Cache Key Task Output Cached Cache misses
68. Remote Build cache • Build cache can be saved remotely • It’s recommended to generate cache from the CI
69. Remote Build cache buildCache { remote<HttpBuildCache> { url = uri(“https: // my-cache-server:8123/cache/“) } }
70. Conclusion • Stop thinking of Gradle as a black box • Treat your build script like real code • Don’t panic ! • Play with it
71. Thank you