Absolutely, you can configure your .aar library to handle Java 8 features in a way that removes the need for downstream developers to manually set compileOptions in their projects. The key is using Android's desugar tool to convert Java 8 bytecode to compatible versions, plus configuring your library to automatically propagate required build settings to dependencies.

Step 1: Enable Core Library Desugaring in Your Library #

Desugaring converts Java 8 language features (like lambdas, default interface methods, and stream APIs) into bytecode that works with older Java versions. Add this to your library module's build.gradle (or build.gradle.kts if using Kotlin):

android {
    compileOptions {
        sourceCompatibility JavaVersion.VERSION_1_8
        targetCompatibility JavaVersion.VERSION_1_8
        // Enable desugaring to convert Java 8 features to compatible bytecode
        coreLibraryDesugaringEnabled true
    }
}

dependencies {
    // Add the desugar library dependency
    coreLibraryDesugaring 'com.android.tools:desugar_jdk_libs:2.0.4'
}

Step 2: Automatically Propagate Compile Options to Dependencies #

To ensure downstream projects inherit the required Java 8 settings without manual configuration, you need to embed these settings in your library's published metadata. If you're publishing to Maven (either locally or a repository), add this publishing configuration:

android {
    publishing {
        publications {
            release(MavenPublication) {
                from components.release
                // Embed Java 8 compile options in the POM file
                pom.properties {
                    property("android.compileOptions.sourceCompatibility", JavaVersion.VERSION_1_8)
                    property("android.compileOptions.targetCompatibility", JavaVersion.VERSION_1_8)
                }
            }
        }
    }
}

Key Notes & Validation #

• AGP Version Requirement: Make sure you're using Android Gradle Plugin (AGP) 3.0.0 or newer (desugaring support was added here). For best results, use AGP 7.0+ to avoid compatibility gaps.
• Test the Setup: Create a test Android project that doesn't have any compileOptions set to Java 8, add your library as a dependency, and verify it builds and runs without errors.
• Advanced Features: If your library uses more advanced Java 8+ features (like Optional or CompletableFuture), the desugar library will handle these as long as you're using an up-to-date version of desugar_jdk_libs.

内容的提问来源于stack exchange，提问作者Sam Stern