APIs power every modern application — mobile apps, microservices, dashboards, IoT devices, and more. And today, developers have three major API technologies to choose from:

• REST (HTTP/JSON)
• gRPC (HTTP/2 + Protocol Buffers)
• GraphQL (single endpoint + flexible queries)

Each has its strengths, weaknesses, and ideal use cases.

🌐 1. REST — The Traditional Standard

REST is the most widely used API style, built around:

• Resources (/users, /orders)
• HTTP verbs (GET, POST, PUT, DELETE)
• JSON as the default format

✔ Strengths

• Easy to understand
• Browser-friendly
• Great tooling
• Good for public APIs

❌ Weaknesses

• Over-fetching
• Under-fetching
• JSON overhead
• HTTP/1.1 latency

Java Example

@RestController
@RequestMapping("/users")
public class UserController {

    @GetMapping("/{id}")
    public User getUser(@PathVariable int id) {
        return new User(id, "John Doe");
    }
}

⚡ 2. gRPC — High-Performance, Low-Latency APIs

gRPC uses:

• HTTP/2
• Protocol Buffers
• Generated client/server code
• Streaming

✔ Strengths

• Extremely fast
• Small binary payloads
• Streaming support
• Strong typing

❌ Weaknesses

• Not browser-native
• Harder to debug binary payloads

gRPC Java Example

user.proto:

syntax = "proto3";

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

message GetUserRequest {
  int32 id = 1;
}

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

Server:

public class UserServiceImpl extends UserServiceGrpc.UserServiceImplBase {

    @Override
    public void getUser(GetUserRequest request, StreamObserver<GetUserResponse> responseObserver) {

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

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

🔍 3. GraphQL — Flexible Queries for Frontend Apps

GraphQL allows clients to request exactly the data they need.

✔ Strengths

• Avoids over-fetching
• Strong schema
• Great for mobile & dashboards

❌ Weaknesses

• Harder caching
• Over-fetching risks in resolvers
• Performance overhead in large graphs

Java Example (Spring GraphQL)

Schema:

type User {
  id: Int
  name: String
}

type Query {
  user(id: Int!): User
}

Resolver:

@Component
public class UserQueryResolver implements GraphQLQueryResolver {
    public User user(int id) {
        return new User(id, "John Doe");
    }
}

🏎 Performance Comparison

🎯 When to Choose What?

✔ Use REST when:

• Building public APIs
• Browser-based clients
• Simplicity matters

✔ Use gRPC when:

• You need performance
• Microservices communicate internally
• You need streaming

✔ Use GraphQL when:

• Frontend needs flexible queries
• You want to avoid over-fetching
• Mobile apps require optimized data loads

🧠 Final Summary

• REST → Simple, universal
• gRPC → Fast, efficient, best for microservices
• GraphQL → Flexible, client-driven

Each excels in different scenarios.