Update Java app (#16)

* add java app

* Update Java app

* Update Java sample app

Author: justinyoo

complete/java/demo/.gitattributes complete/java/.gitattributescomplete/java/demo/.gitattributes renamed to complete/java/.gitattributes

@@ -1,9 +1,367 @@
 # Java App Sample
 
-## Prerequisites
+A comprehensive Spring Boot REST API application for a social media platform with full CRUD operations for posts, comments, and likes.
+
+## Project Overview
+
+This is a production-ready Spring Boot application built with the following specifications:
+
+- **Package Name**: `com.contoso.socialapp`
+- **Artifact ID**: `socialapp`
+- **Group ID**: `com.contoso`
+- **Package Type**: `jar`
+- **Java Version**: OpenJDK 21
+- **Build Tool**: Gradle
+- **Database**: SQLite (embedded)
+- **Port**: 8080
+
+### Project Dependencies
+
+- **Spring Boot 3.2.5**: Core framework
+- **Spring Web**: RESTful API endpoints
+- **Spring Data JPA**: Database operations
+- **Spring Boot Actuator**: Application monitoring
+- **Spring Boot Validation**: Input validation
+- **SQLite**: Embedded database
+- **Hibernate Community Dialects**: SQLite support
+- **Springdoc OpenAPI**: API documentation (Swagger UI)
+- **Lombok**: Boilerplate code reduction
+
+### Project Structure
+
+```text
+src/
+├── main/
+│   ├── java/
+│   │   └── com/
+│   │       └── contoso/
+│   │           └── socialapp/
+│   │               ├── SocialAppApplication.java     # Main application class
+│   │               ├── config/
+│   │               │   ├── WebConfig.java            # CORS configuration
+│   │               │   └── OpenApiConfig.java        # Swagger/OpenAPI config
+│   │               ├── controller/
+│   │               │   ├── HealthController.java     # Health endpoints
+│   │               │   ├── PostController.java       # Post management
+│   │               │   └── CommentController.java    # Comment & like management
+│   │               ├── model/
+│   │               │   ├── Post.java                 # Post entity
+│   │               │   ├── Comment.java              # Comment entity
+│   │               │   ├── Like.java                 # Like entity
+│   │               │   └── dto/                      # Data Transfer Objects
+│   │               ├── repository/
+│   │               │   ├── PostRepository.java       # Post data access
+│   │               │   ├── CommentRepository.java    # Comment data access
+│   │               │   └── LikeRepository.java       # Like data access
+│   │               └── service/
+│   │                   ├── PostService.java          # Post business logic
+│   │                   └── CommentService.java       # Comment business logic
+│   └── resources/
+│       ├── application.properties                    # Application configuration
+│       └── data.sql                                  # Sample data (optional)
+└── test/
+    └── java/
+        └── com/
+            └── contoso/
+                └── socialapp/
+                    └── SocialAppApplicationTests.java # Integration tests
+```
+
+## Features
+
+- ✅ Complete RESTful API for social media operations
+- ✅ Post management (Create, Read, Update, Delete)
+- ✅ Comment system with full CRUD operations
+- ✅ Like/Unlike functionality
+- ✅ SQLite database with JPA/Hibernate
+- ✅ OpenAPI/Swagger documentation
+- ✅ CORS enabled for localhost and GitHub Codespaces
+- ✅ Dynamic server URL configuration
+- ✅ Health check endpoints
+- ✅ Spring Boot Actuator integration
+- ✅ Comprehensive error handling
+- ✅ Input validation with Bean Validation
+
+## Quick Start
+
+### Prerequisites
 
 Refer to the [README](../../README.md) doc for preparation.
 
-## Getting Started
+### 1. Environment Setup
+
+First, set the environment variable of `$REPOSITORY_ROOT`.
+
+```bash
+# bash/zsh
+REPOSITORY_ROOT=$(git rev-parse --show-toplevel)
+```
+
+```powershell
+# PowerShell
+$REPOSITORY_ROOT = git rev-parse --show-toplevel
+```
+
+Then, navigate to the java directory.
+
+```bash
+cd $REPOSITORY_ROOT/complete/java
+```
+
+### 2. Build the Application
+
+```bash
+# Make gradlew executable (if needed)
+chmod +x ./gradlew
+
+# Build the project
+./gradlew build
+```
+
+### 3. Run the Application
+
+```bash
+# Start the application using Gradle
+./gradlew bootRun
+
+# Alternative: Run the JAR file directly
+# java -jar build/libs/socialapp-0.0.1-SNAPSHOT.jar
+```
+
+### 4. Verify Application is Running
+
+```bash
+# Check health endpoint
+curl http://localhost:8080/api/health
+
+# Expected response: {"status":"healthy"}
+```
+
+### 5. Access API Documentation
+
+Open your browser and navigate to:
+
+- **Swagger UI**: [http://localhost:8080/swagger-ui.html](http://localhost:8080/swagger-ui.html)
+- **OpenAPI JSON**: [http://localhost:8080/v3/api-docs](http://localhost:8080/v3/api-docs)
+
+## API Endpoints
+
+### Health & Welcome
+
+- `GET /api/health` - Custom health check endpoint
+- `GET /api/welcome` - Welcome message endpoint
+
+### Posts Management
+
+- `GET /api/posts` - Get all posts
+- `GET /api/posts/{id}` - Get specific post by ID
+- `POST /api/posts` - Create a new post
+- `PATCH /api/posts/{id}` - Update an existing post
+- `DELETE /api/posts/{id}` - Delete a post
+
+### Comments Management
+
+- `GET /api/posts/{postId}/comments` - Get all comments for a post
+- `GET /api/posts/{postId}/comments/{commentId}` - Get specific comment
+- `POST /api/posts/{postId}/comments` - Add a comment to a post
+- `PATCH /api/posts/{postId}/comments/{commentId}` - Update a comment
+- `DELETE /api/posts/{postId}/comments/{commentId}` - Delete a comment
+
+### Likes Management
+
+- `POST /api/posts/{postId}/like` - Like a post
+- `DELETE /api/posts/{postId}/like` - Unlike a post
+
+### Spring Boot Actuator
+
+- `GET /actuator/health` - Spring Boot health indicator
+- `GET /actuator/info` - Application information
+
+## Testing the API
+
+### Using cURL Examples
+
+#### Create a Post
+
+```bash
+curl -X POST http://localhost:8080/api/posts \
+  -H "Content-Type: application/json" \
+  -d '{
+    "title": "My First Post",
+    "content": "This is the content of my first post!",
+    "authorName": "John Doe"
+  }'
+```
+
+#### Get All Posts
+
+```bash
+curl http://localhost:8080/api/posts
+```
+
+#### Add a Comment
+
+```bash
+curl -X POST http://localhost:8080/api/posts/1/comments \
+  -H "Content-Type: application/json" \
+  -d '{
+    "content": "Great post!",
+    "authorName": "Jane Smith"
+  }'
+```
+
+#### Like a Post
+
+```bash
+curl -X POST http://localhost:8080/api/posts/1/like \
+  -H "Content-Type: application/json" \
+  -d '{
+    "userName": "john_doe"
+  }'
+```
+
+### Using Swagger UI
+
+1. Open [http://localhost:8080/swagger-ui.html](http://localhost:8080/swagger-ui.html)
+2. Explore available endpoints
+3. Click "Try it out" on any endpoint
+4. Fill in parameters and click "Execute"
+
+## Development
+
+### Running Tests
+
+```bash
+# Run all tests
+./gradlew test
+
+# Run with coverage report
+./gradlew test jacocoTestReport
+
+# Run specific test class
+./gradlew test --tests "SocialAppApplicationTests"
+```
+
+### Database
+
+The application uses SQLite as an embedded database:
+
+- **Database file**: `sns_api.db` (created automatically)
+- **Location**: Project root directory
+- **Schema**: Auto-generated by Hibernate
+- **Sample data**: Loaded from `data.sql` (if present)
+
+To reset the database, simply delete the `sns_api.db` file and restart the application.
+
+## Configuration
+
+### Application Properties
+
+Key configuration settings in `application.properties`:
+
+```properties
+# Application Settings
+spring.application.name=socialapp
+server.port=8080
+
+# Database Configuration
+spring.datasource.url=jdbc:sqlite:sns_api.db
+spring.jpa.hibernate.ddl-auto=update
+
+# OpenAPI/Swagger Configuration
+springdoc.swagger-ui.path=/swagger-ui.html
+springdoc.swagger-ui.operationsSorter=method
+```
+
+### CORS Configuration
+
+The application supports both localhost and GitHub Codespaces:
+
+- **Localhost**: `http://localhost:8080`
+- **GitHub Codespaces**: Auto-detected and configured dynamically
+
+### Environment Detection
+
+The application automatically detects the runtime environment:
+
+- **Local Development**: Uses `http://localhost:8080`
+- **GitHub Codespaces**: Uses `https://{codespace-name}-8080.{domain}`
+
+## Deployment
+
+### Building for Production
+
+```bash
+# Create production JAR
+./gradlew clean build
+
+# JAR location
+ls -la build/libs/socialapp-0.0.1-SNAPSHOT.jar
+```
+
+### Running in Production
+
+```bash
+# Run with production profile
+java -jar build/libs/socialapp-0.0.1-SNAPSHOT.jar --spring.profiles.active=prod
+
+# Or with custom port
+java -jar build/libs/socialapp-0.0.1-SNAPSHOT.jar --server.port=8081
+```
+
+## Troubleshooting
+
+### Common Issues
+
+#### Port Already in Use
+
+```bash
+# Find process using port 8080
+lsof -i :8080
+
+# Kill the process (replace PID)
+kill -9 <PID>
+
+# Or use a different port
+./gradlew bootRun --args='--server.port=8081'
+```
+
+#### Build Failures
+
+```bash
+# Clean and rebuild
+./gradlew clean build
+
+# Update Gradle wrapper
+./gradlew wrapper --gradle-version=8.5
+```
+
+#### Database Issues
+
+```bash
+# Reset database
+rm sns_api.db
+./gradlew bootRun
+```
+
+### Logs and Monitoring
+
+- **Application logs**: Console output when running `./gradlew bootRun`
+- **Health check**: `GET /actuator/health`
+- **Application info**: `GET /actuator/info`
+
+## Security Considerations
+
+⚠️ **Development Configuration**: The current setup is optimized for development with:
+
+- CORS enabled for all origins
+- SQLite database (not suitable for production scale)
+- No authentication/authorization
+
+For production deployment, consider:
 
-### Run Spring Boot Backend
+- Restricting CORS to specific domains
+- Using PostgreSQL/MySQL instead of SQLite
+- Implementing Spring Security for authentication
+- Adding rate limiting and input sanitization
+- Using HTTPS/TLS encryption