Gradle

Overview

  • Gradle is an open-source build automation tool
  • Build scripts are written in Groovy or Kotlin
  • Official build tool for Android
  • Extensible with plugins
  • Every existing Gradle projects ships with a Gradle wrapper, which means you don’t have to install Gradle to build the project
    • gradlew for Linux
    • gradlew.bat for Windows
  • You can either use Gradle as a CLI or through IDE plugins

Core Model

  • Builds are modeled as _Directed Acyclic Graphs (DAGs) of tasks (units of work)
  • Tasks are wired together based on their dependencies

  • Tasks consist of

    • Actions: pieces of work that do something, like copy files or compile sources
    • Inputs: values, files and directories that actions operate on
    • Outputs: files and directories that actions modify or generate

  • There are several build phases:

    • Initialization: Setup the environment
    • Configuration: Constructs and configures the task graph
    • Execution: Run selected task

  • Build scripts should be declarative instead of imperative

  • Build scripts map to the Gradle API

Build Environment

  • There are multiple ways of configuring Gradle:
    • Command-line flags: Have precedence over properties and environment variables
      • Example: --build-cache
    • System properties
      • Example: systemProp.http.proxyHost=somehost.org stored in gradle.properties
    • Gradle properties
      • Example: org.gradle.caching=true stored in gradle.properties
    • Environment variables

Gradle Daemon

  • Is a long-lived process used for caching
  • It waits in between builds in idle mode
  • Allows Gradle to be loaded into memory only once, instead of for each build

Simple build.gradle

import org.apache.commons.codec.binary.Base64

buildscript {
  repositories {
    mavenCentral()
  }
  dependencies {
    classpath group: "commons-codec", name: "commons-codec", version: "1.2"
  }
}

task hello {
  doLast {
    println "Hello World!"
  }
}

task upper {
  dependsOn hello
  doLast {
    String str = "waynee95"
    println "Original: $str"
    println "Upper case: ${str.toUpperCase()}"
  }
}

Maven vs Gradle

Kotlin DSL

Cheatsheet

Run a task

$ gradle <taskname>

Use gradle -q <taskname> to suppress log messages.

Most builds have clean, check, assemble and build tasks.

List all available tasks

$ gradle tasks

To learn more about any task run gradle help --task <taskname>.

Update gradle wrapper version

$ gradle wrapper --gradle-version=6.4

Run custom jar file

Add this to build.gradle:

task runJflex(type: JavaExec) {
    classpath = files("libs/jflex-full-1.8.2.jar")
    args '/path/to/flex/file'
}

References

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