Building a Server-Side Streaming gRPC Service in Spring Boot: A Stock Ticker Demo

🧠What is gRPC and Why Use It?

This project demonstrates how to implement server-side streaming using gRPC in a Spring Boot application with Java 11. The use case simulates a stock ticker that streams real-time stock prices to the client.

🔧 Technologies Used

• Java 11
• Spring Boot 2.7.x
• gRPC (1.54.0)
• Protocol Buffers (proto3)
• Maven
• WebFlux + Server-Sent Events (SSE) for REST integration

✅Code Repository Link 

Link - grpc-stock-streaming-rest

Generate gRPC Java Code -  mvn clean compile

Run the Application -  mvn spring-boot:run

REST to gRPC Streaming via SSE GET - http://localhost:8080/api/stream?symbol=AAPL

✅ Project Structure

• grpc-stock-streaming/
  ├── pom.xml
  ├── src/
  │   └── main/
  │       ├── java/
  │       │   └── com/
  │       │       └── example/
  │       │           └── grpc/
  │       │               ├── GrpcApplication.java       # Bootstraps Spring Boot
  │       │               ├── StockService.java          # gRPC service implementation
  │       │               ├── StockClient.java           # gRPC client stub (non-blocking)
  │       │               └── StockController.java       # REST API exposing SSE endpoint
  │       ├── proto/
  │       │   └── stock.proto                             # gRPC service + messages
  │       └── resources/
  │           └── application.properties                 # gRPC & Spring server config
  

✅ Class Explanations

---

✅ stock.proto Explained in Detail

• syntax = "proto3";
  option java_multiple_files = true;
  option java_package = "com.example.grpc";
  option java_outer_classname = "StockProto";
  
  service StockTicker {
    rpc StreamStockPrices (StockRequest) returns (stream StockResponse);
  }
  
  message StockRequest {
    string symbol = 1;
  }
  
  message StockResponse {
    string symbol = 1;
    double price = 2;
  }

✅ REST → gRPC Call Flow Diagram

• 
  Browser / Postman / curl
          │
          ▼
  GET /api/stream?symbol=AAPL (SSE endpoint)
          │
          ▼
  StockController
          │
          ▼
  StockClient (gRPC Stub)
          │
          ▼
  [Non-blocking StreamObserver]
          │
          ▼
  gRPC Network Call (localhost:9090)
          │
          ▼
  StockService (on Server)
          │
       [5x response]
          │
          ▼
  StockClient → REST Stream (Flux/SSE) → Browser

🧠 What is gRPC and Why Use It?

❌ gRPC Server-Side Streaming Anti-Patterns

⚙️ gRPC Streaming Performance vs Other Streaming Protocols