musteresel's blog

Build an Android App Bundle (*.aab) from the command line

2019-07-11

tagged: android

Here’s how I’m building an Android App Bundle (*.aab) file from the command line, without Gradle:

  1. Get the necessary tools: aapt2 and bundletool. aapt2 is the second version of the Android Asset Packaging Tool. It’s available (I used manual download from Maven) here. The downloaded jar file contained the aapt2 executable. bundletool is used to work with App bundles, available from it’s GitHub repository. I downloaded bundletool-all-0.10.0.jar, which can be run with java -jar path/to/above/bundletool.jar. Apart from these two the following steps need javac (the Java compiler), jarsigner (part of the JDK for me), dx (part of the Android SDK build tools; used to convert Java bytecode to Dalvik bytecode) and zip/unzip.

  2. “Compile” all resources using aapt2: Every resource file of the base module needs to be compiled:

    aapt2 compile project/app/src/main/res/**/* -o compiled_resources

    This fills the compiled_resources directory with files such as layout_activity_main.xml.flat.

  3. “Link” the resources into a temporary APK, generating the R.java file along the way and converting the resources into protobuf format:

    aapt2 link --proto-format -o temporary.apk \
           -I android_sdk/platforms/android-NN/android.jar \
           --manifest project/app/src/main/AndroidManifest.xml \
           -R compiled_resources/*.flat \
           --auto-add-overlay --java gen

    This creates the temporary.apk which contains the resources and the manifest in protobuf (Google Protocol Buffers) format and also generates R.java (under gen/my/package/R.java) which is used by Java code to reference resources. It needs to “include” (it doesn’t really contain it, just cross-checks references) the android.jar for the target platform (part of the Android SDK).

  4. Compile the Java source files. Since R.java is now generated, I can compile the Java sources:

    javac -source 1.7 -target 1.7 \
      -bootclasspath $JAVA_HOME/jre/lib/rt.jar \
      -classpath android_sdk/platforms/android-NN/android.jar \
      -d classes \
      gen/**/*.java project/app/src/main/java/**/*.java

    This creates .class files in the classes directory. Depending on dependencies the classpath needs to include other paths/jars.

  5. Extract the previously generated temporary APK:

    unzip temporary.apk -d staging

    An APK is nothing but a fancy zip file, so this puts all contents of the temporary.apk into the staging directory.

  6. Prepare files to be bundled as the base module. The end result is a staging directory which can be zipped as a base module. First step is to move the staging/AndroidManifest.xml into staging/manifest/ (a directory to be created). Next I create stating/dex/ and use dx to convert the Java bytecode (in the .class files) to Dalvik bytecode (suitable for running on Android):

    dx --dex --output=staging/dex/classes.dex classes/

  7. Create a zip file of the contents of the base module: (cd staging; zip -r ../base.zip *)

  8. Build the bundle: bundletool build-bundle --modules=base.zip --output=bundle.aab

  9. Sign it: jarsigner -keystore mykeystore.jks bundle.aab my-id

Done :)

Notes: