BMAD-METHOD/expansion-packs/bmad-java/data/java-21-features.md

Java 21 Features and Modernization Guide

Java 21 Language Features

Pattern Matching for Switch

• Description: Enhanced switch expressions with pattern matching
• Use Case: Simplify conditional logic and type checking
• Example:

  switch (obj) {
      case String s -> System.out.println("String: " + s);
      case Integer i -> System.out.println("Integer: " + i);
      case null -> System.out.println("Null value");
      default -> System.out.println("Unknown type");
  }
  

Records

• Description: Immutable data classes with automatic methods
• Use Case: Replace traditional POJOs and DTOs
• Example:

  public record User(String name, String email, int age) {
      public User {
          if (age < 0) throw new IllegalArgumentException("Age cannot be negative");
      }
  }
  

Sealed Classes

• Description: Restrict which classes can extend a class

• Use Case: Model domain hierarchies and improve type safety

• Example:

  public sealed class Shape permits Circle, Rectangle, Triangle {
      public abstract double area();
  }
  
  public final class Circle extends Shape {
      private final double radius;
      public double area() { return Math.PI * radius * radius; }
  }
  

Text Blocks

• Description: Multi-line string literals
• Use Case: SQL queries, JSON, HTML templates
• Example:

  String sql = """
      SELECT u.id, u.name, u.email
      FROM users u
      WHERE u.active = true
      AND u.created_date > ?
      """;
  

Virtual Threads (Project Loom)

• Description: Lightweight threads for high-concurrency applications
• Use Case: I/O-bound applications, microservices
• Example:

  try (var executor = Executors.newVirtualThreadPerTaskExecutor()) {
      executor.submit(() -> {
          // I/O operation
          return processData();
      });
  }
  

Performance Improvements

Garbage Collection Enhancements

• ZGC: Low-latency garbage collector
• G1GC: Improved performance and predictability
• SerialGC: Better performance for small applications
• ParallelGC: Enhanced throughput

JVM Optimizations

• AOT Compilation: Ahead-of-time compilation support
• JIT Improvements: Better just-in-time compilation
• Memory Management: Improved memory allocation and deallocation
• Threading: Enhanced thread management

Security Enhancements

Cryptographic Updates

• TLS 1.3: Enhanced security protocols
• Cryptographic Algorithms: Updated and improved algorithms
• Key Management: Better key handling and storage
• Secure Random: Improved random number generation

Security Headers

• HTTP Security Headers: Enhanced security header support
• Content Security Policy: Better CSP implementation
• CORS: Improved Cross-Origin Resource Sharing
• Authentication: Enhanced authentication mechanisms

API Improvements

Collections Framework

• Immutable Collections: Factory methods for immutable collections
• Stream API: Enhanced stream operations
• Optional: Improved Optional handling
• CompletableFuture: Better async programming support

I/O Improvements

• NIO.2: Enhanced file system operations
• HTTP Client: Built-in HTTP client
• Process API: Improved process management
• File I/O: Better file handling and operations

Migration Strategies

From Java 8 to Java 21

1. Update Dependencies: Check compatibility with Java 21
2. Modernize Code: Use new language features
3. Update Build Tools: Maven/Gradle updates
4. Test Thoroughly: Comprehensive testing
5. Performance Testing: Validate performance improvements

From Java 11 to Java 21

1. Language Features: Adopt new language features
2. Performance Optimization: Leverage performance improvements
3. Security Updates: Implement security enhancements
4. API Updates: Use improved APIs
5. Testing: Validate all changes

From Java 17 to Java 21

1. New Features: Implement new language features
2. Performance Tuning: Optimize for Java 21
3. Security Hardening: Implement security improvements
4. Monitoring: Update monitoring and observability
5. Documentation: Update documentation and guides

Best Practices

Code Modernization

• Use Records: Replace POJOs with records
• Pattern Matching: Simplify conditional logic
• Text Blocks: Use for multi-line strings
• Sealed Classes: Model domain hierarchies
• Virtual Threads: Use for I/O-bound operations

Performance Optimization

• JVM Tuning: Optimize JVM parameters
• Garbage Collection: Choose appropriate GC
• Memory Management: Optimize memory usage
• Threading: Use virtual threads for I/O
• Caching: Implement effective caching strategies

Security Implementation

• Encryption: Use updated cryptographic algorithms
• Authentication: Implement secure authentication
• Authorization: Use proper authorization mechanisms
• Input Validation: Validate all inputs
• Security Headers: Implement security headers

Testing Strategies

• Unit Testing: Comprehensive unit test coverage
• Integration Testing: Test all integrations
• Performance Testing: Validate performance improvements
• Security Testing: Test security implementations
• Compatibility Testing: Test compatibility with dependencies

Migration Checklist

Pre-Migration

• Analyze current Java version and features
• Check dependency compatibility
• Plan migration strategy
• Set up testing environment
• Create rollback plan

During Migration

• Update Java version
• Update dependencies
• Modernize code
• Update build configuration
• Test thoroughly

Post-Migration

• Validate functionality
• Performance testing
• Security testing
• Documentation updates
• Team training

Common Issues and Solutions

Compatibility Issues

• Dependency Conflicts: Resolve version conflicts
• API Changes: Update deprecated APIs
• Build Tool Issues: Update Maven/Gradle
• IDE Issues: Update IDE and plugins

Performance Issues

• Memory Usage: Optimize memory allocation
• Garbage Collection: Tune GC parameters
• Threading: Optimize thread usage
• I/O Operations: Optimize I/O operations

Security Issues

• Cryptographic Updates: Update crypto algorithms
• Security Headers: Implement security headers
• Authentication: Update authentication mechanisms
• Authorization: Implement proper authorization