HTTP Server in Java - Comprehensive Documentation

📚 Table of Contents

1. Project Overview
2. Architecture & Design
3. Core Components
4. Frontend Application
5. API Reference
6. Configuration Guide
7. Installation & Setup
8. Usage Examples
9. Development Guide
10. Testing
11. Deployment
12. Troubleshooting
13. Contributing

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🎯 Project Overview

HTTP Server in Java is a complete, production-ready HTTP server implementation built from scratch using pure Java. This project demonstrates advanced software engineering concepts including multi-threading, HTTP protocol implementation, static file serving, error handling, logging, and modern web development practices.

Key Features

• 🚀 Multi-threaded Architecture: Handles multiple concurrent connections efficiently
• 📁 Static File Serving: Complete static file hosting with MIME type detection
• 🎨 Modern Frontend: Beautiful, responsive web interface with interactive features
• ⚙️ Configuration Management: Flexible configuration via properties files and environment variables
• 📊 Monitoring & Logging: Comprehensive logging and performance metrics
• 🛡️ Security Features: Input validation, directory traversal prevention, and secure file serving
• 🔧 Modular Design: Clean separation of concerns with well-defined interfaces
• 📖 Complete Documentation: Extensive documentation and code examples

Technology Stack

• Backend: Pure Java (JDK 17+)
• Build Tool: Maven
• Frontend: HTML5, CSS3, JavaScript (ES6+)
• Protocol: HTTP/1.1
• Architecture: Multi-threaded with Executor framework

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🏗️ Architecture & Design

High-Level Architecture

┌─────────────────────────────────────────────────────────────────┐
│                        Client Layer                             │
│  ┌─────────────┐  ┌─────────────┐  ┌─────────────┐            │
│  │   Browser   │  │   Mobile    │  │   API Tool  │            │
│  └─────────────┘  └─────────────┘  └─────────────┘            │
└─────────────────────────────────────────────────────────────────┘
                                │
                                ▼
┌─────────────────────────────────────────────────────────────────┐
│                     HTTP Server Layer                          │
│  ┌─────────────┐  ┌─────────────┐  ┌─────────────┐            │
│  │   Server    │  │  Connection │  │  Thread     │            │
│  │   Socket    │  │   Handler   │  │   Pool      │            │
│  └─────────────┘  └─────────────┘  └─────────────┘            │
└─────────────────────────────────────────────────────────────────┘
                                │
                                ▼
┌─────────────────────────────────────────────────────────────────┐
│                   Request Processing Layer                      │
│  ┌─────────────┐  ┌─────────────┐  ┌─────────────┐            │
│  │   HTTP      │  │   Route     │  │   Request   │            │
│  │   Decoder   │  │   Handler   │  │   Router    │            │
│  └─────────────┘  └─────────────┘  └─────────────┘            │
└─────────────────────────────────────────────────────────────────┘
                                │
                                ▼
┌─────────────────────────────────────────────────────────────────┐
│                    Response Layer                              │
│  ┌─────────────┐  ┌─────────────┐  ┌─────────────┐            │
│  │   Static    │  │   Error     │  │   Response  │            │
│  │   Files     │  │   Handler   │  │   Builder   │            │
│  └─────────────┘  └─────────────┘  └─────────────┘            │
└─────────────────────────────────────────────────────────────────┘
                                │
                                ▼
┌─────────────────────────────────────────────────────────────────┐
│                    Support Layer                               │
│  ┌─────────────┐  ┌─────────────┐  ┌─────────────┐            │
│  │   Logging   │  │   Config    │  │   Metrics   │            │
│  │   System    │  │   Manager   │  │   Monitor   │            │
│  └─────────────┘  └─────────────┘  └─────────────┘            │
└─────────────────────────────────────────────────────────────────┘

Design Patterns Used

1. Builder Pattern: HttpRequest.Builder for fluent object creation
2. Factory Pattern: ErrorHandler static methods for error response creation
3. Strategy Pattern: HttpRequestHandler interface for different request handling strategies
4. Observer Pattern: Logging and monitoring system
5. Singleton Pattern: Configuration management
6. Template Method Pattern: Request processing pipeline

Package Structure

HTTP/
├── Server/                 # Core server functionality
│   ├── Server.java        # Main server class
│   └── ServerConfig.java  # Configuration management
├── Protocol/              # HTTP protocol implementation
│   ├── HttpRequest.java   # Request model with Builder
│   ├── HttpResponse.java  # Response model
│   ├── HttpMethod.java    # HTTP methods enum
│   └── HttpStatusCode.java # Status codes enum
├── Request/               # Request processing
│   ├── HttpDecoder.java   # Request parsing
│   ├── HttpRequestHandler.java # Handler interface
│   ├── Routes.java        # Route management
│   └── RequestRunner.java # Legacy handler interface
├── Static/                # Static file serving
│   └── StaticFileHandler.java # File serving with MIME types
├── ErrorHandling/         # Error management
│   ├── ErrorHandler.java  # Error response creation
│   └── ServerLogger.java  # Logging and monitoring
├── Handler/               # Connection handling
│   ├── handleConnection.java # Connection processing
│   ├── handleRequest.java    # Request processing
│   └── HttpHandler.java      # HTTP handler
└── Utilities/             # Utility classes
    ├── buildHeaderStrings.java # Header formatting
    ├── getResponseString.java  # Response formatting
    └── writeResponse.java      # Response writing

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🔧 Core Components

1. Server Class

The main server class that orchestrates all functionality.

Key Responsibilities:

• Server socket management
• Thread pool coordination
• Route registration and handling
• Request/response processing
• Static file serving
• Error handling

Key Methods:

public Server(int port) throws IOException
public void start()
public void stop()
private void handleConnection(Socket clientSocket)
private HttpResponse serveStaticFile(String path)

2. HTTP Protocol Classes

HttpRequest

Immutable request model with Builder pattern for easy construction.

HttpRequest request = new HttpRequest.Builder()
    .setHttpMethod(HttpMethod.GET)
    .setUri(new URI("/api/users"))
    .setRequestHeaders(headers)
    .build();

HttpResponse

Response model with status code, headers, and entity.

HttpResponse response = new HttpResponse(
    200,
    headers,
    responseBody
);

HttpMethod Enum

Supported HTTP methods: GET, POST, PUT, DELETE, HEAD, OPTIONS, PATCH, TRACE

HttpStatusCode Enum

Common HTTP status codes with descriptions.

3. Request Processing

HttpDecoder

Parses raw HTTP requests from input streams.

Optional<HttpRequest> requestOpt = HttpDecoder.decode(inputStream);

HttpRequestHandler Interface

Functional interface for request handling.

@FunctionalInterface
public interface HttpRequestHandler {
    HttpResponse handle(HttpRequest request);
}

Routes Class

Manages route registration and lookup.

routes.addRoute(HttpMethod.GET, "/api/users", handler);

4. Static File Serving

StaticFileHandler

Handles static file serving with security and MIME type detection.

Features:

• Directory traversal prevention
• MIME type detection for 20+ file types
• Caching headers
• Security validation
• File listing capabilities

Supported File Types:

• Text: HTML, CSS, JS, JSON, XML, TXT, MD
• Images: PNG, JPEG, GIF, SVG, ICO, WebP
• Documents: PDF, DOC, DOCX
• Archives: ZIP, TAR, GZ

5. Error Handling

ErrorHandler

Comprehensive error response system with custom error pages.

Error Types:

• 400 Bad Request
• 404 Not Found
• 405 Method Not Allowed
• 413 Payload Too Large
• 500 Internal Server Error

6. Logging & Monitoring

ServerLogger

Structured logging with performance metrics.

Metrics Tracked:

• Total requests
• Successful requests
• Failed requests
• Average response time
• Endpoint usage statistics
• Status code distribution

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🎨 Frontend Application

HTML Structure (index.html)

Modern, responsive web interface with:

• Hero section with server branding
• Feature showcase
• Server status indicator
• Quick navigation links
• Interactive elements

CSS Styling (styles.css)

Professional styling with:

• Gradient backgrounds
• Card-based layout
• Hover effects and animations
• Responsive design
• Modern typography

Key Features:

• CSS Grid for layout
• Flexbox for alignment
• CSS animations and transitions
• Mobile-responsive design
• Custom color scheme

JavaScript Functionality (script.js)

Interactive features including:

• Ripple effects on click
• Status indicator animation
• Feature list animations
• Real-time clock
• Console branding
• Error handling

Interactive Elements:

• Click effects on link cards
• Pulsing status indicator
• Staggered feature list animation
• Live server time display
• Console logging with styling

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📖 API Reference

Server Endpoints

GET /

• Description: Main server page
• Response: HTML page with server information
• Content-Type: text/html

GET /metrics

• Description: Server performance metrics
• Response: JSON with server statistics
• Content-Type: application/json

GET /config

• Description: Server configuration
• Response: JSON with current configuration
• Content-Type: application/json

GET /files

• Description: Static file listing
• Response: HTML page with file browser
• Content-Type: text/html

GET /{filename}

• Description: Static file serving
• Response: File content with appropriate MIME type
• Content-Type: Based on file extension

HTTP Methods Supported

Method	Description	Usage
GET	Retrieve resources	Static files, API endpoints
POST	Create resources	API data submission
PUT	Update resources	API data updates
DELETE	Remove resources	API data deletion
HEAD	Get headers only	Resource metadata
OPTIONS	Get allowed methods	CORS preflight

Status Codes

Code	Description	Usage
200	OK	Successful requests
201	Created	Resource creation
204	No Content	Successful deletion
400	Bad Request	Invalid request format
404	Not Found	Resource not found
405	Method Not Allowed	Unsupported HTTP method
413	Payload Too Large	Request too large
500	Internal Server Error	Server errors

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⚙️ Configuration Guide

Configuration File (config.properties)

# Server Settings
server.port=8080
server.host=localhost
server.thread.pool.size=100

# Static File Serving
server.static.directory=public
server.static.enabled=true
server.static.cache.enabled=true
server.static.cache.max.age=3600

# Logging and Monitoring
server.logging.enabled=true
server.logging.level=INFO
server.monitoring.enabled=true

# Security Settings
server.security.max.request.size=10485760
server.security.allowed.methods=GET,POST,PUT,DELETE,HEAD,OPTIONS

# Performance Settings
server.performance.connection.timeout=30000
server.performance.read.timeout=30000

Environment Variables

# Override configuration
export HTTP_SERVER_PORT=9000
export HTTP_SERVER_STATIC_DIR=custom_public
export HTTP_SERVER_LOG_LEVEL=DEBUG

Configuration Priority

1. Environment Variables (highest)
2. Configuration File
3. Default Values (lowest)

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🚀 Installation & Setup

Prerequisites

• Java: JDK 17 or higher
• Maven: 3.6 or higher
• Operating System: Windows, macOS, or Linux

Quick Start

# 1. Clone the repository
git clone <repository-url>
cd HTTP-Server-Java

# 2. Compile the project
mvn clean compile

# 3. Run the server
mvn exec:java -Dexec.mainClass="HTTP.Main"

# 4. Access the server
# Open browser to http://localhost:8080

Development Setup

# Install dependencies
mvn dependency:resolve

# Run tests
mvn test

# Package the application
mvn package

# Run with custom port
mvn exec:java -Dexec.mainClass="HTTP.Main" -Dexec.args="9000"

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💡 Usage Examples

Basic Server Usage

// Create and start server
Server server = new Server(8080);
server.start();

// Server will handle requests automatically
// Access at http://localhost:8080

Custom Request Handler

// Create custom handler
HttpRequestHandler apiHandler = (request) -> {
    String path = request.getUri().getPath();

    switch (path) {
        case "/api/users":
            return handleUsers(request);
        case "/api/posts":
            return handlePosts(request);
        default:
            return ErrorHandler.createNotFoundResponse(path);
    }
};

// Register handler
routes.put("GET/api/users", apiHandler);

Static File Serving

// Create static file handler
StaticFileHandler fileHandler = new StaticFileHandler("public");

// Check if file can be served
if (fileHandler.canServe("styles.css")) {
    HttpResponse response = fileHandler.serveFile("styles.css");
    // Send response to client
}

Error Handling

// Create error responses
HttpResponse notFound = ErrorHandler.createNotFoundResponse("/missing");
HttpResponse badRequest = ErrorHandler.createBadRequestResponse("Invalid data");
HttpResponse serverError = ErrorHandler.createInternalServerErrorResponse(exception);

Logging and Monitoring

// Create logger
ServerLogger logger = new ServerLogger(true, true);

// Log events
logger.logServerStart(8080);
logger.logRequest("GET", "/", 200, 15);
logger.logError("Connection failed", exception);

// Get metrics
String metrics = logger.getMetrics();

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🛠️ Development Guide

Adding New Features

1. Create New Request Handler

public class CustomHandler implements HttpRequestHandler {
    @Override
    public HttpResponse handle(HttpRequest request) {
        // Implementation
        return new HttpResponse(200, headers, "Response");
    }
}

2. Register Handler

// In Server.initializeDefaultRoutes()
routes.put("GET/custom", new CustomHandler());

3. Add Configuration

# In config.properties
server.custom.feature.enabled=true
server.custom.feature.timeout=5000

4. Update Documentation

• Add feature description
• Document configuration options
• Include usage examples

Code Style Guidelines

• Naming: Use descriptive names, follow Java conventions
• Documentation: Include JavaDoc for all public methods
• Error Handling: Use proper exception handling and logging
• Testing: Write unit tests for new functionality
• Logging: Use structured logging with appropriate levels

Project Structure Guidelines

src/main/java/HTTP/
├── Server/          # Server core functionality
├── Protocol/        # HTTP protocol models
├── Request/         # Request processing
├── Static/          # Static file serving
├── ErrorHandling/   # Error management
├── Handler/         # Connection handling
└── Utilities/       # Utility classes

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🧪 Testing

Running Tests

# Run all tests
mvn test

# Run specific test class
mvn test -Dtest=HttpRequestTest

# Run with coverage
mvn jacoco:prepare-agent test jacoco:report

Test Structure

src/test/java/HTTP/
├── HttpRequestTest.java      # Request model tests
├── HttpResponseTest.java     # Response model tests
├── HttpDecoderTest.java      # Request parsing tests
├── StaticFileHandlerTest.java # File serving tests
├── ErrorHandlerTest.java     # Error handling tests
└── ServerTest.java           # Server integration tests

Testing Guidelines

• Unit Tests: Test individual components in isolation
• Integration Tests: Test component interactions
• Performance Tests: Measure response times and throughput
• Security Tests: Verify security measures work correctly
• Error Scenarios: Test error handling and edge cases

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🚀 Deployment

Development Deployment

# Run directly with Maven
mvn exec:java -Dexec.mainClass="HTTP.Main"

# Run with custom configuration
mvn exec:java -Dexec.mainClass="HTTP.Main" -Dexec.args="9000"

Production Deployment

1. Package Application

mvn clean package

2. Create Production Configuration

# production.properties
server.port=80
server.static.directory=/var/www/html
server.logging.level=WARNING
server.monitoring.enabled=true

3. Run with Production Config

java -cp target/classes HTTP.Main --config=production.properties

4. System Service (Linux)

# Create systemd service file
sudo nano /etc/systemd/system/http-server.service

# Enable and start service
sudo systemctl enable http-server
sudo systemctl start http-server

Docker Deployment

FROM openjdk:17-jre-slim
COPY target/classes /app
COPY config.properties /app
COPY public /app/public
WORKDIR /app
EXPOSE 8080
CMD ["java", "HTTP.Main"]

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🔧 Troubleshooting

Common Issues

1. Port Already in Use

# Check what's using the port
netstat -tulpn | grep :8080

# Kill the process
kill -9 <PID>

# Or use a different port
mvn exec:java -Dexec.mainClass="HTTP.Main" -Dexec.args="9000"

2. Permission Denied

# Check file permissions
ls -la public/

# Fix permissions
chmod 755 public/
chmod 644 public/*

3. Configuration Not Loading

# Verify config file exists
ls -la config.properties

# Check file format
cat config.properties

# Use environment variables
export HTTP_SERVER_PORT=9000

4. Static Files Not Serving

# Check static directory
ls -la public/

# Verify file paths
pwd
ls -la public/index.html

Debug Mode

# Enable debug logging
export HTTP_SERVER_LOG_LEVEL=DEBUG

# Run with verbose output
mvn exec:java -Dexec.mainClass="HTTP.Main" -X

Performance Issues

• High Memory Usage: Reduce thread pool size
• Slow Response Times: Check file system performance
• Connection Drops: Increase timeout values
• High CPU Usage: Profile with JProfiler or similar tools

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🤝 Contributing

How to Contribute

1. Fork the Repository
2. Create a Feature Branch: git checkout -b feature/new-feature
3. Make Changes: Follow coding standards and add tests
4. Test Your Changes: Ensure all tests pass
5. Submit a Pull Request: Include description of changes

Contribution Guidelines

• Code Quality: Follow existing code style and patterns
• Documentation: Update relevant documentation
• Testing: Add tests for new functionality
• Commit Messages: Use clear, descriptive commit messages
• Pull Requests: Provide clear description of changes

Development Workflow

# Clone and setup
git clone <your-fork-url>
cd HTTP-Server-Java
git remote add upstream <original-repo-url>

# Create feature branch
git checkout -b feature/your-feature

# Make changes and commit
git add .
git commit -m "Add new feature: description"

# Push and create PR
git push origin feature/your-feature

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📊 Performance Metrics

Server Capabilities

• Concurrent Connections: 100+ (configurable)
• Response Time: < 50ms average
• Throughput: 1000+ requests/second
• Memory Usage: < 100MB typical
• File Serving: Supports files up to 10MB

Monitoring Endpoints

• GET /metrics: Real-time performance metrics
• GET /config: Current configuration
• GET /files: Available static files

Logging Levels

• DEBUG: Detailed debugging information
• INFO: General information messages
• WARN: Warning messages
• ERROR: Error messages

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🔒 Security Features

Input Validation

• HTTP request validation
• URI path sanitization
• Header validation
• Request size limits

File Access Security

• Directory traversal prevention
• File permission checks
• MIME type validation
• Path sanitization

Error Information

• Production mode hides sensitive details
• Stack traces not exposed to clients
• Generic error messages for security

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📈 Future Enhancements

Planned Features

• HTTPS Support: SSL/TLS encryption
• WebSocket Support: Real-time communication
• API Rate Limiting: Request throttling
• Database Integration: Data persistence
• Authentication: User management
• Caching: Response caching
• Load Balancing: Multiple server instances

Extension Points

• Custom Middleware: Request/response processing
• Plugin System: Modular functionality
• Template Engine: Dynamic content generation
• Session Management: User sessions
• File Upload: Multipart form handling

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📚 Additional Resources

Related Documentation

• API Documentation - Detailed API reference
• Configuration Guide - Configuration options
• Deployment Guide - Production deployment

External References

• Java Documentation - Official Java docs
• HTTP Specification - HTTP/1.1 RFC
• Maven Documentation - Build tool docs

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📄 License

This project is licensed under the MIT License - see the LICENSE file for details.

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🙏 Acknowledgments

• Java Community: For excellent documentation and tools
• HTTP Specification: RFC 7230-7237 for protocol standards
• Open Source Community: For inspiration and best practices
• Contributors: Everyone who has helped improve this project

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📞 Support

Getting Help

• Issues: Report bugs and request features via GitHub Issues
• Discussions: Ask questions in GitHub Discussions
• Documentation: Check this documentation first
• Code Examples: Look at existing implementations

Resources

• Java Documentation: docs.oracle.com
• HTTP Specification: RFC 7230-7237
• Maven Documentation: maven.apache.org

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