最新のマイクロサービスが REST よりも gRPC を好む理由

syntax = "proto3";

option java_multiple_files = true;
option java_package = "com.ghaznix.grpc.payment";
option java_outer_classname = "PaymentProto";

package payment;

// The Payment Service definition
service PaymentService {
  // Unary RPC: Sends a single payment request and receives a confirmation
  rpc ProcessPayment (PaymentRequest) returns (PaymentResponse);
}

// The Payment Request message
message PaymentRequest {
  string transaction_id = 1;
  string customer_id = 2;
  double amount = 3;
  string currency = 4;
}

// The Payment Response message
message PaymentResponse {
  string transaction_id = 1;
  string status = 2;
  string message = 3;
  string timestamp = 4;
}

package com.ghaznix.grpc.payment;

import io.grpc.stub.StreamObserver;
import java.time.Instant;

public class PaymentServiceImpl extends PaymentServiceGrpc.PaymentServiceImplBase {

    @Override
    public void processPayment(PaymentRequest request, StreamObserver<PaymentResponse> responseObserver) {
        System.out.println("Received payment request for customer: " + request.getCustomerId() 
                + " with amount: " + request.getAmount() + " " + request.getCurrency());

        // Process payment logic (simulation)
        String status = request.getAmount() > 0 ? "SUCCESS" : "DECLINED";
        String message = status.equals("SUCCESS") ? "Payment processed successfully." : "Invalid payment amount.";

        PaymentResponse response = PaymentResponse.newBuilder()
                .setTransactionId(request.getTransactionId())
                .setStatus(status)
                .setMessage(message)
                .setTimestamp(Instant.now().toString())
                .build();

        // Send the response to the client
        responseObserver.onNext(response);
        
        // Signal that the RPC execution is complete
        responseObserver.onCompleted();
    }
}

package com.ghaznix.grpc.payment;

import io.grpc.Server;
import io.grpc.ServerBuilder;
import java.io.IOException;
import java.util.concurrent.TimeUnit;

public class PaymentServer {

    private Server server;

    public void start() throws IOException {
        int port = 50051;
        server = ServerBuilder.forPort(port)
                .addService(new PaymentServiceImpl())
                .build()
                .start();
        
        System.out.println("gRPC Server started, listening on port " + port);

        Runtime.getRuntime().addShutdownHook(new Thread(() -> {
            System.err.println("*** Shutting down gRPC server since JVM is shutting down");
            try {
                PaymentServer.this.stop();
            } catch (InterruptedException e) {
                e.printStackTrace(System.err);
            }
            System.err.println("*** Server shut down");
        }));
    }

    public void stop() throws InterruptedException {
        if (server != null) {
            server.shutdown().awaitTermination(30, TimeUnit.SECONDS);
        }
    }

    public void blockUntilShutdown() throws InterruptedException {
        if (server != null) {
            server.awaitTermination();
        }
    }

    public static void main(String[] args) throws IOException, InterruptedException {
        final PaymentServer server = new PaymentServer();
        server.start();
        server.blockUntilShutdown();
    }
}

package com.ghaznix.grpc.payment;

import io.grpc.ManagedChannel;
import io.grpc.ManagedChannelBuilder;
import java.util.concurrent.TimeUnit;

public class PaymentClient {

    private final ManagedChannel channel;
    private final PaymentServiceGrpc.PaymentServiceBlockingStub blockingStub;

    public PaymentClient(String host, int port) {
        // Create a communication channel to the server
        this.channel = ManagedChannelBuilder.forAddress(host, port)
                .usePlaintext() // Disables TLS for local development
                .build();
        
        // Create the synchronous blocking stub
        this.blockingStub = PaymentServiceGrpc.newBlockingStub(channel);
    }

    public void shutdown() throws InterruptedException {
        channel.shutdown().awaitTermination(5, TimeUnit.SECONDS);
    }

    public void executePayment(String txId, String customerId, double amount) {
        PaymentRequest request = PaymentRequest.newBuilder()
                .setTransactionId(txId)
                .setCustomerId(customerId)
                .setAmount(amount)
                .setCurrency("USD")
                .build();

        System.out.println("Sending payment request for: " + txId);
        
        // Execute unary synchronous call
        PaymentResponse response = blockingStub.processPayment(request);
        
        System.out.println("Server Response: " + response.getStatus() + " | " + response.getMessage());
    }

    public static void main(String[] args) throws InterruptedException {
        PaymentClient client = new PaymentClient("localhost", 50051);
        try {
            client.executePayment("TX-99081", "customer-abc-123", 250.75);
        } finally {
            client.shutdown();
        }
    }
}