Develop: gRPC and Java basic implementations;

.vscode/settings.json

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+  "java.configuration.updateBuildConfiguration": "automatic",
+  "editor.formatOnSave": true,
+  "[java]": {
+    "editor.defaultFormatter": "redhat.java",
+    "editor.formatOnSave": true
+  }
+}

apps/grpc/README.md

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+# gRPC Application
+
+A Spring Boot-based microservices application demonstrating gRPC communication patterns between services, including both service-to-service gRPC calls and HTTP REST endpoints for external access.
+
+## 📋 Overview
+
+This application consists of multiple microservices that communicate via gRPC:
+
+- **proto-common**: Shared protobuf definitions for service contracts
+- **user-service**: Backend service providing user management via gRPC (port 9092)
+- **aggregator-service**: API gateway that exposes REST endpoints and communicates with backend services via gRPC clients (port 3001)
+
+## 🏗️ Architecture
+
+```
+┌─────────────────────┐
+│  Client/Frontend    │
+└──────────┬──────────┘
+           │ HTTP/REST
+           ▼
+┌─────────────────────┐
+│ Aggregator Service  │ (Port 3001)
+│  - REST API         │
+│  - gRPC Client      │
+└──────────┬──────────┘
+           │ gRPC
+           ▼
+┌─────────────────────┐
+│   User Service      │ (Port 9092 - gRPC)
+│  - gRPC Server      │ (Port 9090 - HTTP)
+│  - H2 Database      │
+└─────────────────────┘
+```
+
+## 🚀 Quick Start
+
+### Prerequisites
+
+- Java 17 or higher
+- Maven 3.9+ (or use the included `build-and-run.sh` script)
+- Port 3001, 9090, and 9092 available
+
+### Using Nx (Recommended)
+
+The project is integrated with Nx for efficient task execution:
+
+```bash
+# Build all modules
+nx run grpc:build
+
+# Run all services in parallel (dev profile)
+nx run grpc:serve
+
+# Run individual services
+nx run grpc:serve:user          # User service only
+nx run grpc:serve:aggregator    # Aggregator service only
+
+# Run tests
+nx run grpc:test
+
+# Clean build artifacts
+nx run grpc:clean
+```
+
+### Using Maven Directly
+
+```bash
+# From apps/grpc directory
+
+# Build all modules
+mvn clean install -DskipTests
+
+# Run user-service
+mvn spring-boot:run -pl modules/user-service -Dspring-boot.run.profiles=dev
+
+# Run aggregator-service (in separate terminal)
+mvn spring-boot:run -pl modules/aggregator-service -Dspring-boot.run.profiles=dev
+```
+
+### Using the Build Script
+
+```bash
+# Auto-downloads Maven if needed and builds the project
+./build-and-run.sh
+```
+
+## 📦 Modules
+
+### proto-common
+
+Shared protobuf definitions that define the service contracts.
+
+**Location**: `modules/proto-common/src/main/proto/`
+
+- `user-service.proto` - User service RPC definitions
+- `stock-service.proto` - Stock service RPC definitions
+- `common/` - Shared message types
+
+The protobuf files are compiled to Java classes using the `protobuf-maven-plugin`.
+
+### user-service
+
+Backend microservice providing user management functionality via gRPC.
+
+**Ports**:
+- `9090` - HTTP (Health checks, H2 console)
+- `9092` - gRPC Server
+
+**Features**:
+- gRPC service implementation
+- Spring Data JPA with H2 database
+- SQL initialization on startup
+- H2 console available at: http://localhost:9090/h2-console
+
+**Database Configuration** (dev):
+- URL: `jdbc:h2:mem:userdb`
+- Username: `sa`
+- Password: *(empty)*
+
+### aggregator-service
+
+API Gateway that exposes REST endpoints and aggregates data from backend services using gRPC clients.
+
+**Port**: `3001` (HTTP/REST)
+
+**Features**:
+- REST API endpoints for external clients
+- gRPC client to communicate with user-service
+- Protobuf-JSON conversion for REST responses
+- Keep-alive and connection management for gRPC channels
+
+**gRPC Client Configuration**:
+- Target: `localhost:9092` (user-service)
+- Keep-alive: 30s
+- Idle timeout: 5m
+- Max inbound message size: 4MB
+
+## 🔧 Configuration Profiles
+
+The application supports multiple Spring profiles:
+
+- `dev` - Development profile (default)
+- `development` - Extended development configuration
+- `production` - Production configuration
+
+Switch profiles using:
+```bash
+-Dspring-boot.run.profiles=dev
+```
+
+## 🧪 Testing
+
+```bash
+# Run all tests
+nx run grpc:test
+
+# Or with Maven
+mvn test
+```
+
+## 🛠️ Development
+
+### Adding New Services
+
+1. Create a new module in `modules/`
+2. Define service contract in `proto-common/src/main/proto/`
+3. Update parent `pom.xml` to include the new module
+4. Implement gRPC service or client
+5. Update `project.json` for Nx integration
+
+### Protobuf Changes
+
+After modifying `.proto` files:
+
+```bash
+# Rebuild proto-common to regenerate Java classes
+mvn clean install -pl modules/proto-common
+
+# Then rebuild dependent services
+mvn clean install -pl modules/user-service,modules/aggregator-service
+```
+
+## 📊 Monitoring & Debugging
+
+### H2 Database Console
+
+Access the user-service database:
+- URL: http://localhost:9090/h2-console
+- JDBC URL: `jdbc:h2:mem:userdb`
+- Username: `sa`
+- Password: *(empty)*
+
+### Health Checks
+
+- User Service: http://localhost:9090/actuator/health
+- Aggregator Service: http://localhost:3001/actuator/health
+
+### Logging
+
+Both services use colored console logging with service name prefixes:
+- 🔵 USER-SERVICE
+- 🟢 AGGREGATOR-SERVICE
+
+Log levels can be adjusted in `application-dev.properties`.
+
+## 🔐 Dependencies
+
+Key technologies used:
+
+- **Spring Boot** - Application framework
+- **Spring gRPC** (1.0.1) - gRPC integration for Spring
+- **gRPC** - High-performance RPC framework
+- **Protocol Buffers** - Serialization format
+- **Spring Data JPA** - Database access
+- **H2 Database** - In-memory database
+- **Lombok** - Boilerplate reduction
+
+## 📝 Notes
+
+- All services must be running for the aggregator to work properly
+- The aggregator service depends on user-service being available at `localhost:9092`
+- gRPC communication uses plaintext (no TLS) in development mode
+- The build includes automatic protobuf compilation via Maven plugins
+
+## 🤝 Contributing
+
+When making changes:
+
+1. Follow the existing code structure
+2. Update proto definitions in `proto-common` for API changes
+3. Maintain backward compatibility when possible
+4. Add tests for new functionality
+5. Update this README if adding new services or changing configuration
+
+## 📄 License
+
+Part of the gx.java project.

apps/grpc/modules/aggregator-service/pom.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<!--suppress VulnerableLibrariesLocal -->
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <parent>
+        <groupId>com.guan</groupId>
+        <artifactId>grpc-app</artifactId>
+        <version>0.0.1-SNAPSHOT</version>
+        <relativePath>../../pom.xml</relativePath>
+    </parent>
+
+    <artifactId>aggregator-service</artifactId>
+
+    <dependencies>
+        <dependency>
+            <groupId>com.guan</groupId>
+            <artifactId>proto-common</artifactId>
+            <version>${project.version}</version>
+        </dependency>
+        <!-- gRPC Dependencies -->
+        <dependency>
+            <groupId>io.grpc</groupId>
+            <artifactId>grpc-stub</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>io.grpc</groupId>
+            <artifactId>grpc-protobuf</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>org.springframework.grpc</groupId>
+            <artifactId>spring-grpc-spring-boot-starter</artifactId>
+            <version>1.0.1</version>
+        </dependency>
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-web</artifactId>
+        </dependency>
+        <!-- proto to json for REST -->
+        <dependency>
+            <groupId>com.google.protobuf</groupId>
+            <artifactId>protobuf-java-util</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-test</artifactId>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.springframework.boot</groupId>
+                <artifactId>spring-boot-maven-plugin</artifactId>
+                <configuration>
+                    <mainClass>com.gx.aggregator.AggregatorServiceApplication</mainClass>
+                    <skip>false</skip>
+                </configuration>
+            </plugin>
+        </plugins>
+    </build>
+
+</project>

apps/grpc/modules/aggregator-service/src/main/java/com/gx/aggregator/AggregatorServiceApplication.java

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+package com.gx.aggregator;
+
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+
+@SpringBootApplication
+public class AggregatorServiceApplication {
+
+    public static void main(String[] args) {
+        SpringApplication.run(AggregatorServiceApplication.class, args);
+    }
+
+}