Android GRPC Java Tutorial

2021-02-21

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

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 gist:efernie/7580a383724a264e7c74baab0b6cd839

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

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

gist:efernie/498a01bc4a6fae664b8205282c60e9e0

6. Next we add some lines to the module gradle file
   • Add com.google.protobuf to the top in the plugins object gist:efernie/31dc3e27d4eb503786bd04e1049883dc
   • Add the protobuf block, I add this right above the dependencies block gist:efernie/0c5f5deb5689abe157ccc34f3a33c3c2
   • Add the dependencies to the block, the okhttp, grpc-protobuf-lite, grpc-stub, annotations-api

gist:efernie/a5ea8a95453df8844a4601ab0eb6b8e7

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 gist:efernie/59406cb922c66f3a6b8b70d073ccc6d3

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 gist:efernie/93da3fec61f0830547243f237b65ec8a

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 gist:efernie/1bd00f30a05a208ff9c018f79e9b561b

11. Add this code to onCreate gist:efernie/9bc68a94d84681ff69d146da0f3c15ee

12. Add the GrpcTask and code gist:efernie/2784c5b9fb2a376d3245001ae13ce1ce

13. Add the sendGrpcMessage function that will tie to the submit button gist:efernie/5f972cddcc1f2305412ed838fab41f97

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

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

A Kotlin version is coming soon