1. Introduction

gRPC is a high performance, open source RPC framework initially developed by Google. It helps in eliminating boilerplate code and helps in connecting polyglot services in and across data centers.
You can define how you want the information you’re serializing to be structured by defining protocol buffer message types in .proto files. Each protocol buffer message is a small logical record of information, containing a series of name-value pairs.

2. Download project using git

Use the following command to clone this repository:

git clone https://github.com/essentialprogramming/grpc-client-server-schema.git

3. Defining the Service

The Service definition is already defined in proto file. The .proto file contains the description of some methods that can be called remotely with their parameters and return types. This is done in the .proto file using the protocol buffers. Protocol Buffers are also used for describing the structure of the payload messages.

4. Generate Java code based on .proto files

Navigate to grpc-client folder at pom.xml level and execute the following command mvn clean install in order to:

• build the project (generate executable uber-jar)
• generate the classes specified in .proto file

run the newly generated jar with the following command(from the same path) :
java -jar target/grpc-0.0.1-SNAPSHOT-shaded.jar

Navigate to grpc-server folder at pom.xml level and execute the following command mvn clean install in order to:

• build the project (generate executable uber-jar)
• generate the classes specified in .proto file

run the newly generated jar with the following command(from the same path) :
java -jar target/grpc-0.0.1-SNAPSHOT-shaded.jar

5. Create the Server

After the source code in generated in target/generated-sources/protobuf , navigate to grpc-server and create a class in main folder called HelloWorldServiceImpl and populate it as follows :

We shall extend this class and override the hello() method mentioned in our service definition:

public class HelloServiceImpl extends HelloServiceImplBase {
 
    @Override
    public void hello(
      HelloRequest request, StreamObserver<HelloResponse> responseObserver) {
 
        String greeting = new StringBuilder()
          .append("Hello, ")
          .append(request.getFirstName())
          .append(" ")
          .append(request.getLastName())
          .toString();
 
        HelloResponse response = HelloResponse.newBuilder()
          .setGreeting(greeting)
          .build();
 
        responseObserver.onNext(response);
        responseObserver.onCompleted();
    }
}

The default implementation of the abstract class HelloServiceImplBase is to throw runtime exception io.grpc.StatusRuntimeException saying that the method is unimplemented.

In order to run the server we need to start the gRPC server to listen for incoming requests.
Create a new class called GrpcServer and populate it as follows:

public class GrpcServer {
   public static void main(String[] args) {
       Server server = ServerBuilder
         .forPort(8080)
         .addService(new HelloServiceImpl()).build();

       server.start();
       server.awaitTermination();
   }
}

In this code snippet we use the builder to create a gRPC server on specified port (8080) and we add the service that we previously defined HelloServiceImpl
The start() method is starting the server and we are calling awaitTermination() to keep the server running in foreground blocking the prompt.

6. Create the Client

gRPC has a channel construct that abstracts the details like load balancing, connection, connection pulling. The channel is created using the class ManagedChannelBuilder where the only detail that is specified is the address and the port.

After the source code in generated in target/generated-sources/protobuf , navigate to grpc-client and create a class in main folder called GrpcClient and populate it as follows :

public class GrpcClient {
 public static void main(String[] args) {
     ManagedChannel channel = ManagedChannelBuilder.forAddress("localhost", 8080)
       .usePlaintext()
       .build();

     HelloServiceGrpc.HelloServiceBlockingStub stub 
       = HelloServiceGrpc.newBlockingStub(channel);

     HelloResponse helloResponse = stub.hello(HelloRequest.newBuilder()
       .setFirstName("John")
       .setLastName("Smith")
       .build());

     channel.shutdown();
 }
}

7. Run the newly generated classes

• Navigate to grpc-server folder at pom.xml level and execute the following command mvn clean install in order to build the project that uses the newly generated classes (generate executable uber-jar).
  Run the newly generated jar with the following command (from the same path) :
  java -jar target/grpc-0.0.1-SNAPSHOT-shaded.jar

• Navigate to grpc-client folder at pom.xml level and execute the following command mvn clean install in order to build the project that uses the newly generated classes (generate executable uber-jar).
  Run the newly generated jar with the following command (from the same path) :
  java -jar target/grpc-0.0.1-SNAPSHOT-shaded.jar