Android Java GRPC Tutorial

This tutorial is to show you the basic set up to get GRPC working with an Android app using Java as the primary language.

Prerequisites

• https://developer.android.com/studio

Set Up

Were going to be borrowing the example java server from the main grpc-java repo

• clone https://github.com/grpc/grpc-java

• change directories to the examples folder

• execute ./gradlew installDist

• then run ./build/install/examples/bin/hello-world-server

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1. In the Welcome to Android Studio window, click Create New Project.

2. In the Select a Project Template window, select Empty Activity and click Next.
   

3. In the Configure your project window, complete the following:

   • Enter HelloWorldGrpc in the Name field.
   • Select Java Language drop-down menu.
   • Click Finish

4. Open AndroidManifest.xml add this line above the application block.

   • <uses-permission android:name="android.permission.INTERNET" />
   • For reference here is what it should look like

     	<?xml version="1.0" encoding="utf-8"?>
     	<manifest xmlns:android="http://schemas.android.com/apk/res/android"
     	package="com.example.helloworldgrpc">
     	<uses-permission android:name="android.permission.INTERNET" />
     	<application
     	android:allowBackup="true"
     	android:icon="@mipmap/ic_launcher"
     	android:label="@string/app_name"
     	android:roundIcon="@mipmap/ic_launcher_round"
     	android:supportsRtl="true"
     	android:theme="@style/Theme.HelloWorldGrpc">
     	<activity android:name=".MainActivity">
     	<intent-filter>
     	<action android:name="android.intent.action.MAIN" />
     	<category android:name="android.intent.category.LAUNCHER" />
     	</intent-filter>
     	</activity>
     	</application>
     	</manifest>

     view raw AndroidManifest.xml hosted with ❤ by GitHub

5. Open the project gradle file and add this line to the dependencies section

   • classpath "com.google.protobuf:protobuf-gradle-plugin:0.8.14"

     	buildscript {
     	repositories {
     	google()
     	jcenter()
     	}
     	dependencies {
     	classpath "com.android.tools.build:gradle:4.1.2"
     	classpath "com.google.protobuf:protobuf-gradle-plugin:0.8.14"
     	// NOTE: Do not place your application dependencies here; they belong
     	// in the individual module build.gradle files
     	}
     	}

     view raw project.gradle hosted with ❤ by GitHub

6. Next we add some lines to the module gradle file
   

   • Add com.google.protobuf to the top in the plugins object

     	plugins {
     	id 'com.android.application'
     	id 'com.google.protobuf'
     	}

     view raw grpc-andoird-tutorial_build.gradle hosted with ❤ by GitHub
   • Add the protobuf block, I add this right above the dependencies block

     	protobuf {
     	protoc { artifact = 'com.google.protobuf:protoc:3.12.0' }
     	plugins {
     	grpc { artifact = 'io.grpc:protoc-gen-grpc-java:1.35.0'
     	}
     	}
     	generateProtoTasks {
     	all().each { task ->
     	task.builtins {
     	java { option 'lite' }
     	}
     	task.plugins {
     	grpc {
     	option 'lite'
     	}
     	}
     	}
     	}
     	}

     view raw grpc-andoird-tutorial_build-protobuf.gradle hosted with ❤ by GitHub
   • Add the dependencies to the block, the okhttp, grpc-protobuf-lite, grpc-stub, annotations-api

     	dependencies {
     	implementation 'androidx.appcompat:appcompat:1.2.0'
     	implementation 'com.google.android.material:material:1.3.0'
     	implementation 'androidx.constraintlayout:constraintlayout:2.0.4'
     	testImplementation 'junit:junit:4.+'
     	androidTestImplementation 'androidx.test.ext:junit:1.1.2'
     	androidTestImplementation 'androidx.test.espresso:espresso-core:3.3.0'
     	// GRPC Deps
     	implementation 'io.grpc:grpc-okhttp:1.35.0'
     	implementation 'io.grpc:grpc-protobuf-lite:1.35.0'
     	implementation 'io.grpc:grpc-stub:1.35.0'
     	implementation 'org.apache.tomcat:annotations-api:6.0.53'
     	}

     view raw grpc-andoird-tutorial_build-deps.gradle hosted with ❤ by GitHub

7. Now time to add the proto file

   • Your going to want to go to the terminal and create the proto directory in the main folder
   • Then create the proto file, whats great about using gradle and GRPC dependencies is that the proto files are automatically compiled for you touch HelloWorld.proto
   • Add this to the file

     	syntax = "proto3";
     	option java_multiple_files = true;
     	option java_package = "com.example.helloworldgrpc";
     	option java_outer_classname = "HelloWorldProto";
     	package helloworld;
     	service Greeter {
     	rpc SayHello (HelloRequest) returns (HelloReply) {}
     	}
     	message HelloRequest {
     	string name = 1;
     	}
     	message HelloReply {
     	string message = 1;
     	}

     view raw grpc-android-tutorial_helloworld.proto hosted with ❤ by GitHub

8. Lets now add the text fields and buttons to the main activity

   • Open the activity_main.xml file
   • Your going to want to delete the TextView component Your going to want to add these components to the view
   • PlainText three of them, one for the host input, another for the port input and a third for the message
   • TextView for the result message
   • Button for the sending action
   • It doesn't matter how you arrange them, if you wanted to get this done quickly then copy the xml file from step 9

9. Add ID's and settings for the components
   For the host and port, I like to default those to the grpc server

   • Host PlainText component id should equal host
   • Port PlainText component id should equal port
   • Message PlainText component id should equal message
   • Send/Submit Button component id should equal send
   • Result TextView component id should equal result

     	<?xml version="1.0" encoding="utf-8"?>
     	<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
     	xmlns:app="http://schemas.android.com/apk/res-auto"
     	xmlns:tools="http://schemas.android.com/tools"
     	android:layout_width="match_parent"
     	android:layout_height="match_parent"
     	tools:context=".MainActivity">
     	<TextView
     	android:id="@+id/result"
     	android:layout_width="358dp"
     	android:layout_height="473dp"
     	android:layout_marginTop="16dp"
     	android:layout_marginBottom="16dp"
     	android:text="Result"
     	app:layout_constraintBottom_toBottomOf="parent"
     	app:layout_constraintEnd_toEndOf="parent"
     	app:layout_constraintStart_toStartOf="parent"
     	app:layout_constraintTop_toBottomOf="@+id/send" />
     	<EditText
     	android:id="@+id/host"
     	android:layout_width="wrap_content"
     	android:layout_height="wrap_content"
     	android:layout_marginStart="16dp"
     	android:layout_marginTop="16dp"
     	android:ems="10"
     	android:hint="Host"
     	android:inputType="textPersonName"
     	android:text="10.0.2.2"
     	app:layout_constraintStart_toStartOf="parent"
     	app:layout_constraintTop_toTopOf="parent" />
     	<EditText
     	android:id="@+id/port"
     	android:layout_width="153dp"
     	android:layout_height="wrap_content"
     	android:layout_marginStart="12dp"
     	android:layout_marginTop="16dp"
     	android:layout_marginEnd="16dp"
     	android:ems="10"
     	android:hint="Port"
     	android:inputType="textPersonName"
     	android:text="50051"
     	app:layout_constraintEnd_toEndOf="parent"
     	app:layout_constraintHorizontal_bias="1.0"
     	app:layout_constraintStart_toEndOf="@+id/host"
     	app:layout_constraintTop_toTopOf="parent" />
     	<EditText
     	android:id="@+id/message"
     	android:layout_width="380dp"
     	android:layout_height="58dp"
     	android:layout_marginTop="16dp"
     	android:ems="10"
     	android:hint="Message"
     	android:inputType="textPersonName"
     	app:layout_constraintEnd_toEndOf="parent"
     	app:layout_constraintStart_toStartOf="parent"
     	app:layout_constraintTop_toBottomOf="@+id/host" />
     	<Button
     	android:id="@+id/send"
     	android:layout_width="177dp"
     	android:layout_height="36dp"
     	android:layout_marginTop="16dp"
     	android:onClick="sendGrpcMessage"
     	android:text="Submit"
     	app:layout_constraintEnd_toEndOf="parent"
     	app:layout_constraintStart_toStartOf="parent"
     	app:layout_constraintTop_toBottomOf="@+id/message" />
     	</androidx.constraintlayout.widget.ConstraintLayout>

     view raw grpc-android-tutorial_activity_main.xml hosted with ❤ by GitHub
     

10. Now we move on to the code of the MainActivity. Open up the MainActivity file and declare these vars

    • hostEdit
    • portEdit
    • messageEdit
    • sendButton
    • resultText

      	public class MainActivity extends AppCompatActivity {
      	private EditText hostEdit;
      	private EditText portEdit;
      	private EditText messageEdit;
      	private Button sendButton;
      	private TextView resultText;
      	@Override
      	protected void onCreate(Bundle savedInstanceState) {
      	super.onCreate(savedInstanceState);
      	setContentView(R.layout.activity_main);
      	}
      	}

      view raw grpc-andoird-tutorial_vars.java hosted with ❤ by GitHub

11. Add this code to onCreate
    

    	@Override
    	protected void onCreate(Bundle savedInstanceState) {
    	super.onCreate(savedInstanceState);
    	setContentView(R.layout.activity_main);
    	hostEdit = (EditText) findViewById(R.id.host);
    	portEdit = (EditText) findViewById(R.id.port);
    	messageEdit = (EditText) findViewById(R.id.message);
    	sendButton = (Button) findViewById(R.id.send);
    	resultText = (TextView) findViewById(R.id.result);
    	resultText.setMovementMethod(new ScrollingMovementMethod());
    	}

    view raw grpc-andoird-tutorial-oncreate.java hosted with ❤ by GitHub

12. Add the GrpcTask and code
    

    	private static class GrpcTask extends AsyncTask<String, Void, String> {
    	private final WeakReference<Activity> activityReference;
    	private ManagedChannel channel;
    	private GrpcTask(Activity activity) {
    	this.activityReference = new WeakReference<Activity>(activity);
    	}
    	@Override
    	protected String doInBackground(String... params) {
    	String host = params[0];
    	String message = params[1];
    	String portStr = params[2];
    	int port = TextUtils.isEmpty(portStr) ? 0 : Integer.valueOf(portStr);
    	try {
    	channel = ManagedChannelBuilder.forAddress(host, port).usePlaintext().build();
    	GreeterGrpc.GreeterBlockingStub stub = GreeterGrpc.newBlockingStub(channel);
    	HelloRequest request = HelloRequest.newBuilder().setName(message).build();
    	HelloReply reply = stub.sayHello(request);
    	return reply.getMessage();
    	} catch (Exception e) {
    	StringWriter sw = new StringWriter();
    	PrintWriter pw = new PrintWriter(sw);
    	e.printStackTrace(pw);
    	pw.flush();
    	return String.format("Failed... : %n%s", sw);
    	}
    	}
    	@Override
    	protected void onPostExecute(String result) {
    	try {
    	channel.shutdown().awaitTermination(1, TimeUnit.SECONDS);
    	} catch (InterruptedException e) {
    	Thread.currentThread().interrupt();
    	}
    	Activity activity = activityReference.get();
    	if (activity == null) {
    	return;
    	}
    	TextView resultText = (TextView) activity.findViewById(R.id.result);
    	Button sendButton = (Button) activity.findViewById(R.id.send);
    	resultText.setText(result);
    	sendButton.setEnabled(true);
    	}
    	}

    view raw grpc-android-tutorial_grpctask.java hosted with ❤ by GitHub

13. Add the sendGrpcMessage function that will tie to the submit button
    

    	public void sendGrpcMessage(View view) {
    	((InputMethodManager) getSystemService(Context.INPUT_METHOD_SERVICE))
    	.hideSoftInputFromWindow(hostEdit.getWindowToken(), 0);
    	sendButton.setEnabled(false);
    	resultText.setText("");
    	new GrpcTask(this)
    	.execute(
    	hostEdit.getText().toString(),
    	messageEdit.getText().toString(),
    	portEdit.getText().toString());
    	}

    view raw grpc-android-tutorial_sendGrpcMessage.java hosted with ❤ by GitHub

14. Go back to activity_main.xml and set the button onClick listener to sendGrpcMessage
    

15. Run the app on the emulator

    • For the host use 10.0.2.2
    • For the port use 50051
    • Then add a message
    • Click Submit
    • You should get back Hello and what ever you placed in the message component and see it in the result component

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Link to the code for https://github.com/efernie/Android-Java-Grpc-Tutorial

A Kotlin version is coming soon