# Build TensorFlow Lite for Android

This document describes how to build TensorFlow Lite Android library on your
own. Normally, you do not need to locally build TensorFlow Lite Android library.
If you just want to use it, the easiest way is using the
[TensorFlow Lite AAR hosted at JCenter](https://bintray.com/google/tensorflow/tensorflow-lite).
See [Android quickstart](../guide/android.md) for more details on how to use
them in your Android projects.

## Build TensorFlow Lite locally

In some cases, you might wish to use a local build of TensorFlow Lite. For
example, you may be building a custom binary that includes
[operations selected from TensorFlow](https://www.tensorflow.org/lite/guide/ops_select),
or you may wish to make local changes to TensorFlow Lite.

### Set up build environment using Docker

*   Download the Docker file. By downloading the Docker file, you agree that the
    following terms of service govern your use thereof:

*By clicking to accept, you hereby agree that all use of the Android Studio and
Android Native Development Kit will be governed by the Android Software
Development Kit License Agreement available at
https://developer.android.com/studio/terms (such URL may be updated or changed
by Google from time to time).*

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*   You can optionally change the Android SDK or NDK version. Put the downloaded
    Docker file in an empty folder and build your docker image by running:

```shell
docker build . -t tflite-builder -f tflite-android.Dockerfile
```

*   Start the docker container interactively by mounting your current folder to
    /host_dir inside the container (note that /tensorflow_src is the TensorFlow
    repository inside the container):

```shell
docker run -it -v $PWD:/host_dir tflite-builder bash
```

If you use PowerShell on Windows, replace "$PWD" with "pwd".

If you would like to use a TensorFlow repository on the host, mount that host
directory instead (-v hostDir:/host_dir).

*   Once you are inside the container, you can run the following to download
    additional Android tools and libraries (note that you may need to accept the
    license):

```shell
android update sdk --no-ui -a --filter tools,platform-tools,android-${ANDROID_API_LEVEL},build-tools-${ANDROID_BUILD_TOOLS_VERSION}
```

You can now proceed to the "Build and Install" section. After you are finished
building the libraries, you can copy them to /host_dir inside the container so
that you can access them on the host.

### Set up build environment without Docker

#### Install Bazel and Android Prerequisites

Bazel is the primary build system for TensorFlow. To build with it, you must
have it and the Android NDK and SDK installed on your system.

1.  Install the latest version of the [Bazel build system](https://bazel.build/versions/master/docs/install.html).
2.  The Android NDK is required to build the native (C/C++) TensorFlow Lite
    code. The current recommended version is 17c, which may be found
    [here](https://developer.android.com/ndk/downloads/older_releases.html#ndk-17c-downloads).
3.  The Android SDK and build tools may be obtained
    [here](https://developer.android.com/tools/revisions/build-tools.html), or
    alternatively as part of
    [Android Studio](https://developer.android.com/studio/index.html). Build
    tools API >= 23 is the recommended version for building TensorFlow Lite.

#### Configure WORKSPACE and .bazelrc

Run the `./configure` script in the root TensorFlow checkout directory, and
answer "Yes" when the script asks to interactively configure the `./WORKSPACE`
for Android builds. The script will attempt to configure settings using the
following environment variables:

*   `ANDROID_SDK_HOME`
*   `ANDROID_SDK_API_LEVEL`
*   `ANDROID_NDK_HOME`
*   `ANDROID_NDK_API_LEVEL`

If these variables aren't set, they must be provided interactively in the script
prompt. Successful configuration should yield entries similar to the following
in the `.tf_configure.bazelrc` file in the root folder:

```shell
build --action_env ANDROID_NDK_HOME="/usr/local/android/android-ndk-r18b"
build --action_env ANDROID_NDK_API_LEVEL="21"
build --action_env ANDROID_BUILD_TOOLS_VERSION="28.0.3"
build --action_env ANDROID_SDK_API_LEVEL="23"
build --action_env ANDROID_SDK_HOME="/usr/local/android/android-sdk-linux"
```

### Build and install

Once Bazel is properly configured, you can build the TensorFlow Lite AAR from
the root checkout directory as follows:

```sh
bazel build -c opt --fat_apk_cpu=x86,x86_64,arm64-v8a,armeabi-v7a \
  --host_crosstool_top=@bazel_tools//tools/cpp:toolchain \
  //tensorflow/lite/java:tensorflow-lite
```

This will generate an AAR file in `bazel-bin/tensorflow/lite/java/`. Note
that this builds a "fat" AAR with several different architectures; if you don't
need all of them, use the subset appropriate for your deployment environment.

Caution: Following feature is experimental and only available at HEAD. You can
build smaller AAR files targeting only a set of models as follows:

```sh
bash tensorflow/lite/tools/build_aar.sh \
  --input_models=model1,model2 \
  --target_archs=x86,x86_64,arm64-v8a,armeabi-v7a
```

Above script will generate the `tensorflow-lite.aar` file and optionally the
`tensorflow-lite-select-tf-ops.aar` file if one of the models is using
Tensorflow ops. For more details, please see the
[Reduce TensorFlow Lite binary size](../guide/reduce_binary_size.md) section.

#### Add AAR directly to project

Move the `tensorflow-lite.aar` file into a directory called `libs` in your
project. Modify your app's `build.gradle` file to reference the new directory
and replace the existing TensorFlow Lite dependency with the new local library,
e.g.:

```
allprojects {
    repositories {
        jcenter()
        flatDir {
            dirs 'libs'
        }
    }
}

dependencies {
    compile(name:'tensorflow-lite', ext:'aar')
}
```

#### Install AAR to local Maven repository

Execute the following command from your root checkout directory:

```sh
mvn install:install-file \
  -Dfile=bazel-bin/tensorflow/lite/java/tensorflow-lite.aar \
  -DgroupId=org.tensorflow \
  -DartifactId=tensorflow-lite -Dversion=0.1.100 -Dpackaging=aar
```

In your app's `build.gradle`, ensure you have the `mavenLocal()` dependency and
replace the standard TensorFlow Lite dependency with the one that has support
for select TensorFlow ops:

```
allprojects {
    repositories {
        jcenter()
        mavenLocal()
    }
}

dependencies {
    implementation 'org.tensorflow:tensorflow-lite:0.1.100'
}
```

Note that the `0.1.100` version here is purely for the sake of
testing/development. With the local AAR installed, you can use the standard
[TensorFlow Lite Java inference APIs](../guide/inference.md) in your app code.
