Android Gradle: Add Native .so Dependencies

Background 

A few months ago, I wrote a Key-Value database for Android called SnappyDB based on Google’s LevelDB.  Since it uses native C++ code, the generated bundle contains (.so) binaries libs, along with Jars. 

Distribution via Maven repo is not a problem (As soon as you pass the hassle of the publishing process:), maven-android-plugin can help you include the shared libs. Maven dependencies convention allows you to specify the type of ABI (different CPU architectures) & the format of the library (obviously .so in our case) you want to resolve using classifier: 

Ex: resolving ARM shared lib for SnappyDB:

<dependency>
  <groupId>com.snappydb</groupId>
  <artifactId>snappydb-native</artifactId>
  <version>0.2.0</version>
  <classifier>armeabi</classifier>
  <type>so</type>
</dependency>

This approach works fine if you use Maven & Eclipse ADT as a build system, until you succumbed to Gradle’s siren call! 

dependencies {
     classpath 'commons-io:commons-io:2.4'
}

but it struggles when it comes to native dependencies, as compared with Maven, you can’t¹ write something like this:

dependencies {
       classpath 'com.snappydb:snappydb-native:2.+:arm-v7a'
}

This is due to the fact that the NDK support is still a work in progress with Android plugin. (as with Android Studio).

jniLibs to the rescue!

In their 0.7.2  release of the Android plugin, Google introduced a new folder ‘jniLibs‘ to the source sets. This means, that you can now add your prebuilt .so files to this folder, and Android plugin will take care of packaging those native libraries inside your APK.

.
├── AndroidManifest.xml
└── jniLibs
    ├── armeabi
    │   └── libsnappydb-native.so
    ├── armeabi-v7a
    │   └── libsnappydb-native.so
    ├── mips
    │   └── libsnappydb-native.so
    └── x86
        └── libsnappydb-native.so

This feature is great, but the developer still need to download & copy his prebuilt .so files manually, which isn’t great especially if you use a Continuous Integration server like Jenkins or Travis for instance. 

So, you get the picture. There has to be a better way.

Meet android-native-dependencies

android-native-dependenciesis a Gradle plugin I wrote to automate the process of resolving & downloading & copying the native dependencies into jniLibs folder, so Android plugin can include them automatically in your APK build. 

The plugin uses the same repository declared to resolve regular dependencies (jar) here is an example:

buildscript {
  repositories {
    mavenCentral()
  }
  dependencies {
    classpath 'com.android.tools.build:gradle:0.10.+'
    classpath 'com.nabilhachicha:android-native-dependencies:0.1'
  }
}

apply plugin: 'android'
apply plugin: 'android-native-dependencies'

native_dependencies {
    artifact 'com.snappydb:snappydb-native:0.2+:armeabi'
    artifact 'com.snappydb:snappydb-native:0.2+:x86'
}

dependencies {
    //regular Jar dependencies ...
}

Convention

The artifact DSL follows the naming convention for Maven artifacts. thus, you can use one of the following syntax: 

//adding x86 classifier will resolve only intel's (.so) lib
native_dependencies {
    artifact 'com.snappydb:snappydb-native:0.2+:x86'
}

//omit the classifier will resolve all supported architectures
native_dependencies {
    artifact 'com.snappydb:snappydb-native:0.2+'
}

• map-style notation

//adding x86 classifier will resolve only intel's (.so) lib
native_dependencies {
    artifact group: 'com.snappydb', name: 'snappydb-native', version: '0.2+', classifier: 'x86'
}

//omit the classifier will resolve all supported architectures
native_dependencies {
    artifact group: 'com.snappydb', name: 'snappydb-native', version: '0.2+'
}

In both notations, classifier is optional. this means that when omitted, the plugin try to resolve the artifacts for all architectures: armeabi, armeabi-v7a, x86 and mips. 

Another great Gradle plugin I recommend is the android-sdk-manager  by (Jake Wharton) who helps downloads and manages your Android SDK.