spring-xu / groovy-android-gradle-plugin

A Gradle plugin to support the Groovy language for building Android apps

Groovy language support for Android

This plugin adds support for writing Android applications using the Groovy language.

Usage

Edit your build.gradle file with the following:

buildscript {
    repositories {
        jcenter()
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:1.5.0'
        classpath 'org.codehaus.groovy:gradle-groovy-android-plugin:0.3.7'
    }
}

apply plugin: 'groovyx.grooid.groovy-android'

Then you must choose which version and modules of Groovy you use. So far, Android support is available in the 2.4.0 release and beyond, so you need to add the following repository to your build.gradle file:

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

Then you can start using Groovy by adding a dependency on the grooid classifier:

dependencies {
    compile 'org.codehaus.groovy:groovy:2.4.5:grooid'
}

then use the assembleDebug task to test.

Should you want to test development versions of the plugin, you can add the snapshot repository and depend on a SNAPSHOT:

buildscript {
    repositories {
        jcenter()
        maven {
            url = 'http://oss.jfrog.org/artifactory/oss-snapshot-local'
        }
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:1.5.0'
        classpath 'org.codehaus.groovy:gradle-groovy-android-plugin:0.3.8-SNAPSHOT'
    }
}

Where to put sources?

Groovy sources must be found inside src/main/groovy. Note that the plugin follows the behavior of the Groovy plugin in Gradle, which means that if you want to be able to have Groovy classes referencing Java classes that themselves reference Groovy classes, then those Java classes must be found inside src/main/groovy too (this is called joint compilation).

Writing Groovy code

This plugin has been successfully tested with Android Studio. It will let you write an application in Groovy. It is recommended, for performance, memory and battery life, that you use @CompileStatic wherever possible.

Details can be found on my blog and here for more technical details

Configuring the Groovy compilation options

The default language level for both source and target is 1.6. You can change it by giving some options. Following example changes it to 1.7. Note that you have to change Android Studio project settings as well if you use the IDE.

project.androidGroovy {
    options {
        sourceCompatibility = '1.7'
        targetCompatibility = '1.7'
    }
}

Similarily, the Groovy compilation tasks can be configured in the androidGroovy block using the options block:

project.androidGroovy {
    options {
        configure(groovyOptions) {
            encoding = 'UTF-8'
            forkOptions.jvmArgs = ['-noverify'] // maybe necessary if you use Google Play Services
        }
        sourceCompatibility = '1.7'
        targetCompatibility = '1.7'
    }
}

Android packagingOptions

Groovy Extension Modules and Global transformations both need a file descriptor in order to work. Android packaging has a restriction related to files having the same name located in the same path.

If you are using several Groovy libraries containing extension modules or/and global transformations, Android may complain about those files.

You can simply add the following rule:

packagingOptions {
    exclude 'META-INF/services/org.codehaus.groovy.transform.ASTTransformation'
    exclude 'META-INF/services/org.codehaus.groovy.runtime.ExtensionModule'
}

There is no problem excluding global transformation descriptors because those are only used at compile time, never at runtime.

The problem comes with module extensions. Unless you statically compile classes using extension modules with @CompileStatic they won't be available at runtime and you'll have a runtime exception.

There is an alternative. The emerger gradle plugin add those excludes for you and merges all extension module descriptors in a single file which will be available at runtime.