gRPC User Service (Java)

A simple Java-based gRPC service demonstrating client–server communication with Protocol Buffers.
Supports Create User, Get User by ID, and List Users with proper gRPC status codes.

📂 Project Structure

simple-user-mgmt-svc/
│
├─ src/main/proto/
│  └─ user_service.proto
│
├─ src/main/java/org/example/grpc/
│  ├─ server/
│  │  └─ UserServer.java          # boots the gRPC server (port 50051)
│  ├─ service/
│  │  └─ UserServiceImpl.java     # in-memory implementation of RPCs
│  └─ client/
│     └─ UserClient.java          # sample blocking client
│
├─ pom.xml
└─ README.md

Note: gRPC/Protobuf stubs are generated under target/generated-sources/protobuf during build and are not checked into source control.

---

🚀 Build & Run

1) Build + generate stubs

mvn clean install

2) Run the server

• From IDE: run org.example.grpc.server.UserServer.main
• CLI (if you have maven-exec-plugin configured):

mvn exec:java -Dexec.mainClass=org.example.grpc.server.UserServer

3) Run the client

• From IDE: run org.example.grpc.client.UserClient.main
• CLI (if you have maven-exec-plugin configured):

mvn exec:java -Dexec.mainClass=org.example.grpc.client.UserClient

---

🛠 Features

• CreateUser — adds a user (name, email)
• GetUser — fetches a user by ID
• ListUsers — returns all users
• Uses proper gRPC Status codes (e.g., INVALID_ARGUMENT, NOT_FOUND)

---

📊 Sample Output

INFO: User created by ID: 1
INFO: User created by ID: 2
INFO: Users List: [id: "1", name: "Alice", email: "alice@example.com",
                   id: "2", name: "Bob",   email: "bob@example.com"]
INFO: User Retrieved: Alice
SEVERE: Failed with status: NOT_FOUND - User not found with id 10

---

🖼 Architecture

+-------------------+      gRPC (Protobuf)      +------------------+
|    UserClient     |  <--------------------->  |    UserServer    |
| (blocking stub)   |                           |  (port 50051)    |
+-------------------+                           +------------------+
          |                                                |
          |  CreateUser / GetUser / ListUsers              |
          v                                                v
                                   org.example.grpc.service.UserServiceImpl

---

Notes

• Server listens on localhost:50051.
• .proto lives in src/main/proto/user_service.proto.
• Generated sources are under target/generated-sources/protobuf after build.