gRPC vs REST in Java: 7 Things Every Microservices Developer Should Know

gRPC vs REST in Java: 7 Things Every Microservices Developer Should Know

When building microservices in Java, one important architectural decision is choosing how services communicate.

For years, REST has been the default choice. But gRPC is becoming an increasingly interesting alternative, especially when performance, strongly typed contracts, and efficient service-to-service communication matter.

So, what's the difference? And when should you choose one over the other?

Let's explore seven things every Java microservices developer should know.

---

1. REST uses JSON, while gRPC uses Protocol Buffers

REST APIs commonly exchange data using JSON.

JSON is human-readable, easy to debug, and supported by almost every programming language.

gRPC uses Protocol Buffers (Protobuf), a compact binary serialization format.

Instead of defining your API through JSON examples or separate documentation, you describe your service in a ".proto" file.

For example:

syntax = "proto3";

service Greeter {
rpc SayHello (HelloRequest) returns (HelloReply);
}

message HelloRequest {
string name = 1;
}

message HelloReply {
string message = 1;
}

From this definition, gRPC can generate client and server code.

Why does this matter?

• Strongly typed service contracts.
• Less repetitive boilerplate.
• Compact message serialization.
• Code generation for multiple programming languages.

1. gRPC is built around HTTP/2

REST commonly uses HTTP/1.1, although it can also run over HTTP/2.

gRPC is designed around HTTP/2 and takes advantage of several of its capabilities:

• Multiplexing: multiple requests can share a single connection.
• Header compression: reduces repeated header overhead.
• Binary framing: provides an efficient transport format.
• Streaming: supports continuous data exchange.

These features make gRPC particularly interesting for communication between backend services.

1. gRPC supports four communication patterns

Traditional REST APIs typically follow a request-response model.

gRPC supports four communication patterns:

Pattern| How it works
Unary RPC| One request, one response
Server streaming| One request, multiple responses
Client streaming| Multiple requests, one response
Bidirectional streaming| Client and server exchange multiple messages

This flexibility makes gRPC useful for real-time applications, monitoring systems, event-driven architectures, and services that need continuous data exchange.

1. gRPC provides strongly typed service contracts

With REST, API contracts are often documented separately using tools such as OpenAPI.

With gRPC, the ".proto" file defines:

• Service names.
• RPC methods.
• Request messages.
• Response messages.
• Field types.

The same contract can be shared between teams and used to generate client and server code.

This helps reduce inconsistencies between services and makes API evolution more structured.

1. When should you choose REST?

REST is still an excellent choice.

Consider REST when:

• You're building public APIs for web or mobile applications.
• Browser compatibility is important.
• Human-readable JSON is useful.
• You need straightforward integration with third-party services.
• Your application mainly exposes conventional CRUD operations.

REST has a mature ecosystem and remains a practical choice for many applications.

1. When should you choose gRPC?

gRPC is particularly useful when:

• Java microservices communicate internally.
• Efficient serialization and transport matter.
• You need client-side or server-side streaming.
• Multiple services share strongly typed contracts.
• Your architecture includes services written in different programming languages.

For internal service-to-service communication, gRPC can be a very effective alternative to REST.

1. Building gRPC microservices with Java and Micronaut

Micronaut provides a lightweight framework for building Java microservices.

Combined with gRPC and Protocol Buffers, it offers a practical foundation for implementing strongly typed service-to-service communication.

If you want to experiment with this approach without starting from scratch, I've created a project:

gRPC Micronaut Starter Kit

The starter kit provides a foundation for building Java gRPC microservices with Micronaut.

Explore the project:

• "GitHub repository" (https://github.com/frekost/grpc-micronaut-starter-kit)
• "Extended version on Gumroad" (https://frekost.gumroad.com/l/grpc2micronaut)

If you'd like to start with a practical introduction, you can also read my previous tutorial:

"Master Java gRPC with Micronaut: Your First Microservice in Minutes" (https://dev.to/frekost/master-java-grpc-with-micronaut-your-first-microservice-in-minutes-6l2)

---

Final thoughts

REST and gRPC are not technologies where one must always replace the other.

They solve different problems.

REST remains an excellent option for public APIs and browser-facing applications.

gRPC is a strong choice for efficient communication between backend services, especially when strongly typed contracts and streaming are important.

In many microservice architectures, both technologies can coexist.

What do you use for communication between Java microservices?

Do you prefer REST, gRPC, or a combination of both?

Share your experience in the comments. I'd love to hear your thoughts!