Gradle

Key Concepts:

1. Gradle Build Scripts

Gradle uses Domain-Specific Languages (DSL) for defining build scripts.

• Groovy or Kotlin DSL: Build scripts can be written in Groovy (build.gradle) or Kotlin (build.gradle.kts).

• Tasks: Everything in Gradle revolves around tasks. Tasks can:

  • Execute commands like compiling code.
  • Run unit tests.
  • Package applications (e.g., .jar, .war).

• Build Lifecycle:

  • Initialization: Determines which project to build.
  • Configuration: Evaluates project scripts and sets up a task graph.
  • Execution: Executes tasks based on the task graph.

2. Dependency Management

Gradle simplifies managing dependencies for a project by automatically downloading and managing external libraries.

• Repositories: Gradle looks for dependencies in specified repositories, such as Maven Central, JCenter, or custom repositories.
• Configurations: Logical groupings of dependencies. Common ones include:
  • implementation: For compiling the main code.
  • testImplementation: For test-specific dependencies.
• Scopes:
  • Compile-time: Dependencies available during compilation.
  • Runtime: Dependencies available only during runtime.
  • Test: Dependencies available only for testing.

Example:

repositories {
    mavenCentral()
}

dependencies {
    implementation("org.jetbrains.kotlin:kotlin-stdlib:1.8.0")
    testImplementation("junit:junit:4.13.2")
}

3. Plugins

Gradle can be extended with plugins that add specific functionality, enabling tasks like building Java projects or working with Android.

• Core Plugins: Built-in plugins like java, kotlin, application.
• Third-Party Plugins: External plugins from Gradle Plugin Portal or custom plugins.
• Custom Plugins: You can create custom plugins to extend build behavior.

Example:

plugins {
    id("org.jetbrains.kotlin.jvm") version "1.8.0"
    id("application")
}

4. Multi-Project Builds

Gradle supports organizing large projects into multiple smaller subprojects that share configurations.

• Settings File (settings.gradle.kts): This file defines which projects belong to the build.
• Subprojects: Subprojects can have their own build scripts or inherit from the root build script.

Example:

rootProject.name = "my-multi-project"
include("projectA", "projectB")

5. Task Configuration

Tasks are central to Gradle’s functioning. You can create, configure, and control task execution.

• Custom Tasks: You can define tasks to perform specific actions.
• Task Dependencies: You can specify dependencies between tasks to control their execution order.

Example of a Custom Task:

tasks.register("hello") {
    doLast {
        println("Hello, Gradle!")
    }
}

• Task Inputs and Outputs: Gradle optimizes task execution by caching outputs based on inputs to avoid redundant executions.

6. Gradle Wrapper

The Gradle Wrapper (gradlew) ensures the project uses a specific version of Gradle without requiring local installation.

• Installation: The Wrapper is created using the gradle wrapper command.
• Usage: Execute ./gradlew build instead of gradle build to use the wrapper and guarantee consistent builds across environments.

Example:

./gradlew clean build