gRPC protoc Android Java Client

Android Java-Lite protoc generated GrpcServiceClient Example​

This Android gRPC Example differentiates from the Java gRPC Example by using the more appropriate Java Lite which results in a much smaller code size making it more suitable to be used on embedded Java platforms like Android.

In addition it uses the Android-compatible OK HTTP SSL Libraries in-place of Netty's SSL libraries and a custom services.proto allow us to specify the Java package we want the generated gRPC client to use.

Install x dotnet tool:

Create a new Android App with Android Studio:

Add protoc generated TodoWorld DTOs and gRPC GrpcServicesStub:

cd app\src\main\java
x proto-java https://todoworld.servicestack.net

Modify the downloaded services.proto to use the package name of your App, e.g:

option java_package = "net.servicestack.androidapp";

Generate a java-lite protoc gRPC client from your modified services.proto:

Update build.gradle with required gRPC, protobuf and OK HTTP plugins and dependencies:

plugins {
    id 'com.google.protobuf' version '0.8.8'
    id 'idea'
}

//...

def grpcVersion = '1.27.0'

dependencies {
    implementation 'javax.annotation:javax.annotation-api:1.2'
    implementation "io.grpc:grpc-protobuf:${grpcVersion}"
    implementation "io.grpc:grpc-auth:${grpcVersion}"
    implementation "io.grpc:grpc-census:${grpcVersion}"
    implementation "io.grpc:grpc-okhttp:${grpcVersion}"
    implementation "io.grpc:grpc-stub:${grpcVersion}"

//...
}

Sync changes to your build.gradle to install the new dependencies:

Add the android.permission.INTERNET to your AndroidManifest.xml (before <application/> tag):

<uses-permission android:name="android.permission.INTERNET"/>

Use protoc generated DTOs and async GrpcServicesStub to perform non-blocking TodoWorld gRPC Service requests:

Android Java protoc gRPC insecure Example​

ManagedChannel channel = ManagedChannelBuilder.forAddress(
    "todoworld.servicestack.net", 50054).usePlaintext().build();

final GrpcServicesGrpc.GrpcServicesStub client =
    GrpcServicesGrpc.newStub(channel);

fab.setOnClickListener(new View.OnClickListener() {
    client.getHello(Services.Hello.newBuilder()
        .setName("Android gRPC").build(),
        new StreamObserver<Services.HelloResponse>() {
            @Override
            public void onNext(Services.HelloResponse value) {
                Snackbar.make(view, value.getResult(), Snackbar.LENGTH_LONG)
                        .setAction("Action", null).show();
            }
            @Override public void onError(Throwable t) {}
            @Override public void onCompleted() {}
        });
});

Now run your App and click the Action button to make a plain-text gRPC Request:

Android Java protoc gRPC SSL Example​

To use gRPC SSL we'll need a copy of our gRPC's Service SSL Certificate which we can make available to our Android App by saving it to our App's assets directory:

mkdir ..\assets
x get https://todoworld.servicestack.net/grpc.crt -out ../assets

Building an TLS Channel configured with a self-signed SSL Certificate requires a bit of effort with OK HTTP so we'll include a ChannelBuilder.java to wrap up the boiler plate:

This simplifies the configuration required down to just the grpc.crt certificate loaded from the App's Asset Manager, the host and port name of the gRPC SSL Channel:

ManagedChannel channel = null;
InputStream is = null;
try {
    is = getResources().getAssets().open("grpc.crt");
    channel = ChannelBuilder.buildTls(
        "todoworld.servicestack.net", 50051, is);
    is.close();
} catch (Throwable e) {
    e.printStackTrace();
}

Lets update the gRPC API call to reflect we're now using an SSL channel:

client.getHello(Services.Hello.newBuilder()
    .setName("gRPC SSL").build(),

Now after re-running our App it'll perform gRPC SSL Service requests instead:

Refer to /mobile/java/AndroidGrpc for a complete example project.