Java Rules

Version: Java 21 LTS

Tooling

• Build: Maven or Gradle
• Testing: JUnit 5 with coverage >= 85%
• Linting: SpotBugs, PMD, Error Prone

Spring Boot 3.2+ Configuration

# Enable virtual threads
spring.threads.virtual.enabled=true

Best Practices (2026)

• Use Virtual Threads for I/O-intensive workloads (reduces memory footprint)
• Use records for immutable data classes
• Use pattern matching in switch expressions
• Use Scoped Values instead of ThreadLocal (for virtual thread compatibility)
• Use Structured Concurrency for managing related task groups

Virtual Threads Caveats

• Avoid synchronized blocks with blocking I/O (causes thread pinning)
• Watch for connection pool exhaustion - tune database pools
• Not all libraries are virtual-thread friendly yet
• Test thoroughly when migrating from platform threads

Concurrency Patterns

// Virtual thread executor
try (var executor = Executors.newVirtualThreadPerTaskExecutor()) {
    executor.submit(() -> processRequest(request));
}

// Structured concurrency (preview)
try (var scope = new StructuredTaskScope.ShutdownOnFailure()) {
    Future<User> user = scope.fork(() -> fetchUser(id));
    Future<Profile> profile = scope.fork(() -> fetchProfile(id));
    scope.join().throwIfFailed();
    return new Response(user.get(), profile.get());
}

MoAI Integration

• Use Skill("moai-lang-java") for detailed patterns
• Follow TRUST 5 quality gates