Modern distributed applications demand high-performance communication between services. While REST over HTTP/1.1 has served us well, microservices, streaming systems, IoT, and high-throughput backends now require more efficient, low-latency alternatives.

Enter gRPC — Google's high-performance RPC framework that combines Protocol Buffers, HTTP/2, and code-generated clients to deliver unmatched speed.

In this article, we’ll explore:

• What gRPC is
• How gRPC works internally
• Why gRPC is incredibly fast
• gRPC streaming types
• A practical Java example (client + server)
• When to use gRPC vs REST

🌐 What Is gRPC?

gRPC is a Remote Procedure Call (RPC) framework that allows you to call methods on a remote server as if they were local functions.

It is built on three core pillars:

1. Protocol Buffers (binary serialization)
2. HTTP/2 transport
3. Strongly-typed auto-generated client/server code

This enables efficient communication between services written in different languages (Java, Go, Python, Node.js, C#, Rust, etc.).

🧠 How gRPC Works

1. Define your API using Protocol Buffers

You write a .proto file defining:

• Services
• RPC methods
• Request/response message types

Example: user.proto

syntax = "proto3";

package user;
option java_multiple_files = true;

service UserService {
  rpc GetUser(GetUserRequest) returns (GetUserResponse);
}

message GetUserRequest {
  int32 id = 1;
}

message GetUserResponse {
  int32 id = 1;
  string name = 2;
}

Compile the proto file:

protoc --java_out=./generated --grpc-java_out=./generated user.proto

This generates:

• Java classes for your messages
• A service interface for the server
• A client stub for the client

🚀 Why gRPC Is So Performant

Let’s break down the magic behind gRPC’s performance.

1. HTTP/2 Instead of HTTP/1.1

HTTP/2 provides:

✔ Multiplexing

Multiple requests sent at the same time over one TCP connection.

✔ Header Compression (HPACK)

Reduces repeated metadata, saving bandwidth.

✔ Server Push

Great for real-time streaming.

2. Protocol Buffers Are Extremely Efficient

ProtoBuf messages shrink payloads dramatically—often by 70–90%—and encode/decode extremely fast.

3. Auto-generated Code = Speed

gRPC generates:

• Server base classes
• Strongly typed client stubs
• Efficient serialization logic

No slow reflection or manual parsing.
Just fast, compiled logic.

4. Streaming Is a First-Class Feature

gRPC supports:

Combined with HTTP/2, these are extremely lightweight and low latency.

💻 Building a gRPC Service in Java

Let’s build a full working example.

1️⃣ Implement the gRPC Server

UserServiceImpl.java

package user;

import io.grpc.stub.StreamObserver;

public class UserServiceImpl extends UserServiceGrpc.UserServiceImplBase {

    @Override
    public void getUser(GetUserRequest request, StreamObserver<GetUserResponse> responseObserver) {
        int id = request.getId();

        GetUserResponse response = GetUserResponse.newBuilder()
                .setId(id)
                .setName("John Doe")
                .build();

        responseObserver.onNext(response);
        responseObserver.onCompleted();
    }
}

2️⃣ Start the gRPC Server

GrpcServer.java

import io.grpc.Server;
import io.grpc.ServerBuilder;

public class GrpcServer {

    public static void main(String[] args) throws Exception {
        Server server = ServerBuilder
                .forPort(9090)
                .addService(new UserServiceImpl())
                .build();

        System.out.println("🚀 gRPC Server running on port 9090");
        server.start();
        server.awaitTermination();
    }
}

Run it:

java GrpcServer

3️⃣ Implement the gRPC Client

GrpcClient.java

import io.grpc.ManagedChannel;
import io.grpc.ManagedChannelBuilder;
import user.GetUserRequest;
import user.UserServiceGrpc;

public class GrpcClient {

    public static void main(String[] args) {

        ManagedChannel channel = ManagedChannelBuilder
                .forAddress("localhost", 9090)
                .usePlaintext()
                .build();

        UserServiceGrpc.UserServiceBlockingStub client =
                UserServiceGrpc.newBlockingStub(channel);

        GetUserRequest request = GetUserRequest.newBuilder()
                .setId(1)
                .build();

        var response = client.getUser(request);

        System.out.println("User name: " + response.getName());
        channel.shutdown();
    }
}

✔ Example Output

User name: John Doe

📌 When Should You Use gRPC?

• High-performance microservices
• Real-time streaming (chat, telemetry, IoT)
• Low-latency systems (trading, gaming)
• Polyglot architectures
• Internal service communication

❌ When Not to Use gRPC

• Public browser APIs (unless using gRPC-Web)
• When debugging readability matters
• When simple JSON over HTTP is enough

🏁 Conclusion

gRPC is incredibly fast because it brings together:

• HTTP/2 (multiplexing, header compression, low latency)
• Protocol Buffers (compact, binary, efficient)
• Generated stubs (optimized, type-safe code)
• Built-in streaming capabilities

With just a .proto file, you can generate a fully working Java client and server that communicate efficiently at scale.

If your system needs speed, scalability, and real-time communication, gRPC is one of the best tools available today.