Gradle¶

Install¶

In Windows 10 WSL, install sdkman

sudo apt install zip
curl -s "https://get.sdkman.io" | bash
source "$HOME/.sdkman/bin/sdkman-init.sh"
sdk version

Install gradle

sdk install gradle
gradle -v

Create a gradle project (for Java)

cd /mnt/d/code/gradle
gradle init --type java-application

You can now use ./gradlew or gradlew.bat in the project folder

Usage with Java¶

Example for the JVM

Common commands¶

./gradlew tasks in your project directory lists which tasks you can run in your project, such as building or running your code.
./gradlew projects
./gradlew properties

Most commonly used Java tasks:

./gradlew build will compile your project's code into a /build folder.
./gradlew run will run the compiled code in your build folder.
./gradlew clean will purge that build folder.
./gradlew test will execute unit tests without building or running your code again.

Build process¶

Gradle launches as a new JVM process
It parses the gradle.properties file and configures Gradle accordingly
Next, it creates a Settings instance for the build
Then, it evaluates the settings.gradle file against the Settings object
It creates a hierarchy of Projects, based on the configured Settings object
Finally, it executes each build.gradle file against its project

In case of a multi-project build, we'd probably have multiple different build.gradle files, one for each project. The build.gradle file is executed against a Project instance, with one Project instance created per subproject.

Groovy DSL¶

Every Gradle build is made up of one or more projects. What a project represents depends on what it is that you are doing with Gradle. For example, a project might represent a library JAR or a web application.

Each project is made up of one or more tasks. A task represents some atomic piece of work which a build performs. This might be compiling some classes, creating a JAR, generating Javadoc, or publishing some archives to a repository.

Tasks¶

Tasks are snippets that we can run directly from the command line in our project directory via ./gradlew [TASK_NAME]

./gradlew copy

task copy(type: Copy, group: "Custom", description: "Copies sources to the dest directory") {
    from "src"
    into "dest"
}

// accessing task properties
println copy.destinationDir
println project.copy.destinationDir

task('copy2', type: Copy) {
    description 'Copies the resource directory to the target directory.'
    from(file('src'))
    into(buildDir)
    include('**/*.txt', '**/*.xml', '**/*.properties')
    timeout = Duration.ofMillis(50000)
}

task hello {
    group = 'Worthless tasks'
    description = 'An utterly useless task'
    // extra (custom) properties
    ext.myProperty = "myValue"
    doLast {
        println 'Hello world!'
    }
}

// API call
hello.doLast {
    println "Greetings from the $hello.name task."  // accessing task property in interpolated string
}

hello.configure {
    doLast {
        println 'Hello again'
    }
}

task next {
    dependsOn hello   // or 'hello' if lazy initialized - task dependency 
    doLast {
       println hello.myProperty
    }
}

./gradlew -q hello
./gradlew -q next

// dynamic tasks
4.times { counter ->
    task "task$counter" {
        doLast {
            println "I'm task number $counter"
        }
    }
}

// default tasks
defaultTasks 'task0', 'task1'

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

// dependencies for the build script
buildscript {
    repositories {
        mavenCentral()
    }
    dependencies {
        classpath group: 'commons-codec', name: 'commons-codec', version: '1.2'
    }
}

task encode {
    doLast {
        // using the build script dependencies
        def byte[] encodedString = new Base64().encode('hello world\n'.getBytes())
        println new String(encodedString)
    }
}

// you can also declare methods
File[] fileList(String dir) {
    file(dir).listFiles({file -> file.isFile() } as FileFilter).sort()
}

Plugins¶

https://plugins.gradle.org/

plugins {
    id "base"
}

Essential plugins for Java:

plugins {
    id 'java'
    id 'application'
}

apply plugin:'application'

Dependencies and repositories¶

repositories {
    jcenter()  // or mavenCentral()
}

dependencies {
    implementation 'com.google.guava:guava:26.0-jre'  // implementation is a configuration defined by the java plugin
    compile group: 'mysql', name: 'mysql-connector-java', version: '5.1.13'

    testImplementation 'junit:junit:4.12'
}

// pointer to the Java entrypoint
mainClassName="com.someorg.someprj.App"