Optional Gradle dependencies for Maven libraries

Question

I'm working on an Android library and would like to use a dependency only if the project using my library includes that dependency as well. Similar to what Picasso does with OkHttp.

I already took care of this on the main code by checking for ClassNotFoundExceptions but it still includes the dependencies upon deploying it to Maven Central. How do I generate something such as Maven's <optional>true</optional> tag?

I'm using gradle-mvn-push to deploy my artifacts via Gradle.

Answer 1

The Nebula Extra Configurations Gradle plugin seems to be providing optional.

You would use it like this:

apply plugin: 'java'
apply plugin: 'nebula.optional-base'

repositories {
    mavenCentral()
}

dependencies {
    compile 'org.apache.commons:commons-lang3:3.3.2', optional
    compile group: 'log4j', name: 'log4j', version: '1.2.17', optional
}

Answer 2

According to this blog, Compile-only dependencies address a number of use cases, including:

• Dependencies required at compile time but required at runtime only when using certain features, a.k.a. optional dependencies;
• Dependencies required at compile time but never required at runtime, such as source-only annotations or annotation processors;
• Dependencies whose API is required at compile time but whose implementation is to be provided by a consuming library, application or runtime environment.

So just using compileOnly to declare an optional dependency.