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Byte buddy Android Gradle plugin

This plugin shares some similarities with the plain Java Byte Buddy Gradle plugin, so it's worth having a look at its readme first.

The Android version of Byte Buddy works similarly to how Android's annotation processors (or kapt for Kotlin) work in the sense that you'd need to define your "compiler" project, which will be a separate project containing the instrumentation code, where the Byte Buddy API is used to create your own Byte Buddy Plugin that will run at compile time of the host Android project.

In order to add your compiler plugin to an Android project, you'd first need to apply the Byte Buddy Gradle plugin to said Android project, the same way as the plain Java Byte Buddy Gradle plugin is added, shown below. Then you need to add your compiler plugin as a dependency of the Android project, but said dependency needs to be of type byteBuddy. This custom type of dependency is used at compile time, but won't be present at runtime. So, if your compiler plugin needs to add classes that will be referenced at runtime, then those classes will have to be added as a separate, regular dependency, as shown below.

build.gradle
plugins {
    id 'com.android.application'
    id 'net.bytebuddy.byte-buddy-gradle-plugin' version byteBuddyVersion
}

dependencies {
    byteBuddy "my.plugin:compiler:0.0.0"
    implementation "my.plugin:library:0.0.0"
}

Creating a Plugin project

A plugin project is a Gradle project that can be either a regular java-library or com.android.library type of project. The advantage of defining it as an Android Library project (com.android.library) is that you'd be able to reference other Android libraries from it, and also Android SDK classes as well.

For your compiler plugin to be able of getting recognized as a Byte Buddy compiler project, it must contain its Byte Buddy plugins class names listed in the META-INF/net.bytebuddy/build.plugins resource file (same way as for the plain Java Byte Buddy Gradle plugin).

Limitations

There are limitations to this tool in comparison to the plain Java Byte Buddy Gradle plugin, caused by the Android environment, those are:

  • You cannot instrument classes that belong to the Android SDK.
  • You can instrument libraries only on Android application projects, not Android libraries projects.
  • You cannot use ByteBuddy.intercept(MethodDelegation) since it requires the creation of additional classes, and the ASM API that this tools is based on, doesn't allow to create new classes.