Chapter 42. Initialization Scripts

Initialization scripts (a.k.a. init scripts) are similar to other scripts in Gradle. These scripts, however, are run before the build starts. Here are several possible uses:

One main limitation of init scripts is that they cannot access classes in the buildSrc project (see Section 41.4, “Build sources in the buildSrc project” for details of this feature).

There are several ways to use an init script:

If more than one init script is found they will all be executed, in the order specified above. Scripts in a given directory are executed in alphabetical order. This allows, for example, a tool to specify an init script on the command line and the user to put one in their home directory for defining the environment and both scripts will run when Gradle is executed.

Similar to a Gradle build script, an init script is a Groovy script. Each init script has a Gradle instance associated with it. Any property reference and method call in the init script will delegate to this Gradle instance.

Each init script also implements the Script interface.

repositories {
    mavenCentral()
}

task showRepos << {
    println "All repos:"
    println repositories.collect { it.name }
}

allprojects {
    repositories {
        mavenLocal()
    }
}

> gradle --init-script init.gradle -q showRepos
All repos:
[MavenLocal, MavenRepo]

In Section 41.6, “External dependencies for the build script” it was explained how to add external dependencies to a build script. Init scripts can also declare dependencies. You do this with the initscript() method, passing in a closure which declares the init script classpath.

initscript {
    repositories {
        mavenCentral()
    }
    dependencies {
        classpath group: 'org.apache.commons', name: 'commons-math', version: '2.0'
    }
}

The closure passed to the initscript() method configures a ScriptHandler instance. You declare the init script classpath by adding dependencies to the classpath configuration. This is the same way you declare, for example, the Java compilation classpath. You can use any of the dependency types described in Section 23.4, “How to declare your dependencies”, except project dependencies.

Having declared the init script classpath, you can use the classes in your init script as you would any other classes on the classpath. The following example adds to the previous example, and uses classes from the init script classpath.

import org.apache.commons.math.fraction.Fraction

initscript {
    repositories {
        mavenCentral()
    }
    dependencies {
        classpath group: 'org.apache.commons', name: 'commons-math', version: '2.0'
    }
}

println Fraction.ONE_FIFTH.multiply(2)

> gradle --init-script init.gradle -q doNothing
2 / 5

Similar to a Gradle build script or a Gradle settings file, plugins can be applied on init scripts.

apply plugin:EnterpriseRepositoryPlugin

class EnterpriseRepositoryPlugin implements Plugin<Gradle> {

    private static String ENTERPRISE_REPOSITORY_URL = "https://repo.gradle.org/gradle/repo"

    void apply(Gradle gradle) {
        // ONLY USE ENTERPRISE REPO FOR DEPENDENCIES
        gradle.allprojects{ project ->
            project.repositories {

                // Remove all repositories not pointing to the enterprise repository url
                all { ArtifactRepository repo ->
                    if (!(repo instanceof MavenArtifactRepository) ||
                          repo.url.toString() != ENTERPRISE_REPOSITORY_URL) {
                        project.logger.lifecycle "Repository ${repo.url} removed. Only $ENTERPRISE_REPOSITORY_URL is allowed"
                        remove repo
                    }
                }

                // add the enterprise repository
                maven {
                    name "STANDARD_ENTERPRISE_REPO"
                    url ENTERPRISE_REPOSITORY_URL
                }
            }
        }
    }
}

repositories{
    mavenCentral()
}

 task showRepositories << {
    repositories.each{
        println "repository: ${it.name} ('${it.url}')"
    }
}

> gradle -q -I init.gradle showRepositories
repository: STANDARD_ENTERPRISE_REPO ('https://repo.gradle.org/gradle/repo')

The plugin in the init script ensures that only a specified repository is used when running the build.

When applying plugins within the init script, Gradle instantiates the plugin and calls the plugin instance's Plugin.apply(T) method. The gradle object is passed as a parameter, which can be used to configure all aspects of a build. Of course, the applied plugin can be resolved as an external dependency as described in Section 42.4, “External dependencies for the init script”