Relocate the package namespace to avoid collisions with other libraries

Introduction

If there are Duplicate classes found in a jetified version of android build and it fails when using aar, one of the reason could be duplicate sub packages from two or more dependencies

One way to solve this problem is to rename the package name in one of the aar, to avoid naming collision. This process is called shadowing the package

Installation

1. Create a Java project with Gradle as the build system and Groovy as the Gradle DSL
2. Add a shadow plugin to the build.gradle

plugins {
  id 'com.gradleup.shadow' version '8.3.5'
  id 'java'
}

Create Tasks

Extract aar

Create a task called extractAar which takes the sourceAar and extract it’s contents and puts under extractedAar folder under the build directory

task extractAar(type: Copy) {  
    def sourceAAR = project.hasProperty('sourceAar') ? project.sourceAar : null  
    from {  
        zipTree(sourceAAR)  
    }  
    into "$buildDir/extractedAar"  
}

Relocate Package names

Use shadowJar to relocate packages under the aar.

shadowJar {  
    dependsOn extractAARs  
  
    from("$buildDir/extractedAar") {  
        include 'classes.jar'    
        // Relocate dependencies        
        relocate 'org.apache.commons.codec', 'shadow.org.apache.commons.codec'  
  
        archiveFileName = "merged-classes.jar"  
    }  
}

This Task should run only after extracting aar. The from("$buildDir/extractedAar") block needs the Source Directory. Let’s pass the extractedAar Directory.

The aar file will have the classes.jar file where the package need to be relocated. So include it in the task.

Pass the package name for which the Duplicate Classes error occurred. In my scenario apache commons package. This will change the package name of org.apache.commons.codec package to shadow.org.apache.commons.codec

Finally mention the archive file name. Here it’s called as merged-classes.jar

Prepare aar

task prepareAar(type: Jar) {  
    dependsOn shadowJar  
  
    from("$buildDir/libs") {  
        include "merged-classes.jar"  
        rename "merged-classes.jar", "classes.jar"  
        into ''  
    }  
  
    from("$buildDir/extractedAar") {  
        exclude 'classes.jar' 
        into ''  
    }  
}

Finally, create the main task prepareAar, which is dependent on shadowJar task.

Here we take the merged-classes/jar which is built in shadowJar step and rename it back to classes.jar and put in the root build directory.

Next take all the files in the extractedAar folder except classes.jar as we need repackaged classes.jar from shadowJar and put it in the root buid directory

After running this, you will find a jar file with the project name. If my preject name is rename-aar-package it will be rename-aar-package.jar

Rename this rename-aar-package.jar to rename-aar-package.aar and use it

The flow is

1. Run the prepareAar task
2. This will trigger shadowJar task
3. shadowJar will trigger extractAar task and extracts the aar
4. Use the extracted aar folder and relocate packaged in shadowJar task
5. Finally Repackage the jar

The Command Would be

./gradlew clean prepareAAR -PsourceAAR=libs/protean-esign-v-3.8_UAT.aar