Essential Cursor Rules for Java Quarkus Projects: Boost Productivity and Code Quality

Unlock the full potential of Cursor AI for Quarkus development with these comprehensive rules. Follow best practices for generating robust, testable Java code tailored to Quarkus frameworks.

Introduction to Cursor Rules for Quarkus Development

Cursor, an AI-powered code editor, excels in accelerating Java development, especially with Quarkus—a Kubernetes-native Java framework renowned for its supersonic startup times and low memory footprint. These rules provide a structured approach to leveraging Cursor's Composer feature for Quarkus projects. By adhering to them, developers can ensure consistent, high-quality code that aligns with Quarkus conventions, includes comprehensive tests, and integrates seamlessly with modern DevOps practices.

Quarkus emphasizes reactive programming, GraalVM native compilation, and extensions for everything from databases to cloud services. Cursor rules help automate repetitive tasks, suggest idiomatic implementations, and prevent common pitfalls. For real-world context, consider the Quarkus Super Heroes demonstrator project on GitHub, which showcases microservices built with Quarkus—perfect for testing these rules.

Core Principles for Using Cursor in Quarkus Projects

1. Prioritize Quarkus Idioms and Best Practices

Always instruct Cursor to generate code following official Quarkus guidelines. Reference the Quarkus GitHub repository for the latest patterns. Key directives include:

• Use @RestController or JAX-RS annotations over Spring stereotypes.
• Leverage CDI for dependency injection with @Inject.
• Opt for Mutiny for reactive streams instead of RxJava unless specified.

Example Prompt for Cursor:

Generate a REST endpoint in Quarkus to fetch heroes from Panache ORM. Use Mutiny Uni for async response, include OpenAPI annotations, and ensure it's native-compatible.

This produces code like:

@Path("/heroes")
@ApplicationScoped
public class HeroResource {

    @Inject
    HeroRepository repository;

    @GET
    @Produces(MediaType.APPLICATION_JSON)
    public Uni<List<Hero>> getAll() {
        return repository.listAll();
    }
}

Adding value: Quarkus extensions like quarkus-rest and quarkus-hibernate-orm-panache simplify this—always check pom.xml for proper dependencies before generation.

2. Mandate Tests for Every Code Generation

Cursor must create unit, integration, and mutation tests alongside application code. Use Quarkus Test extensions (quarkus-junit5, quarkus-rest-client-reactive-testing).

• Unit Tests: @QuarkusUnitTest with mocks via @Mock.
• Integration Tests: @QuarkusIntegrationTest for full stack.
• Mutation Testing: Integrate PITest for code coverage >80%.

Practical Example: When adding a service, prompt:

Create a HeroService with business logic to validate hero powers. Include @QuarkusUnitTest, RestAssured for integration, and assert coverage.

Result includes:

@QuarkusUnitTest
public class HeroServiceTest {

    @InjectMock
    HeroRepository mockRepo;

    @Inject
    HeroService service;

    @Test
    void testValidatePower() {
        // assertions
    }
}

Pro Tip: Run mvn test post-generation to verify. This rule catches 90% of regressions early.

3. Handle Configurations and Properties Correctly

Quarkus uses application.properties or YAML for configs. Direct Cursor to:

• Place runtime props under %prod. prefix.
• Use @ConfigProperty with defaults.
• Support profiles: dev, test, prod.

Step-by-Step:

1. Identify config needs (e.g., DB URL).
2. Prompt: "Add datasource config for PostgreSQL in application.properties, with profile-specific values."
3. Generated:

# application.properties
quarkus.datasource.db-kind=postgresql
quarkus.datasource.username=${DB_USER}
%prod.quarkus.datasource.password=${DB_PASS_PROD}

Enhancement: Integrate with Kubernetes ConfigMaps for cloud deployments.

4. Optimize for Native Compilation

Quarkus shines with GraalVM. Ensure Cursor generates reflection-free code:

• Use @RegisterForReflection sparingly.
• Prefer build-time initialization.
• Test with mvn package -Pnative.

Example: For JSON serialization,

Implement a DTO with Jackson, ensure native compat, no dynamic proxies.

5. Extension Management and Dependency Hygiene

Never hardcode dependencies. Prompt Cursor to:

• List required extensions (e.g., quarkus-resteasy-reactive, quarkus-panache).
• Update pom.xml or build.gradle.
• Run mvn quarkus:add-extension simulation.

Real-World Application: In the Quarkus UI repo, extensions handle WebSocket and caching—replicate this structure.

Advanced Rules for Complex Features

Reactive Programming with Mutiny

Mandate Uni and Multi over blocking calls:

@GET
@Path("/{id}")
public Uni<Hero> getById(@PathParam("id") Long id) {
    return repository.findById(id);
}

Why? Enables backpressure and scales to millions of requests.

Database Interactions with Panache

Use active record or repository patterns:

• Active: Extend PanacheEntityBase.
• Repo: @Repository with PanacheRepository.

Prompt example:

Create Panache repo for Villain entity with CRUD, pagination, and full-text search.

Security Integration

Always include quarkus-elytron-security-common or OIDC:

• @RolesAllowed
• JWT propagation.

Dev UI and Live Reload

Leverage Quarkus Dev UI: mvn quarkus:dev for hot reload. Instruct Cursor to add health checks (quarkus-smallrye-health).

Project Structure Guidelines

Enforce standard layout:

/src/main/java/
  - org.acme.HelloResource.java
/src/test/java/
  - HeroResourceTest.java
pom.xml
application.properties

Step-by-Step Project Setup with Cursor:

1. Prompt: "Initialize a new Quarkus app with REST, Panache, and native build."
2. Generate pom.xml skeleton.
3. Add extensions via codegen.
4. Create Dockerfile for containerization.

CI/CD and Deployment Rules

• Generate GitHub Actions workflows for build/test/deploy.
• Include Dockerfiles optimized for distroless images.
• Kubernetes manifests with quarkus-kubernetes extension.

Example Workflow Snippet:

name: Build
on: [push]
jobs:
  build:
    runs-on: ubuntu-latest
    steps:
    - uses: actions/checkout@v2
    - name: Build
      run: mvn package -Pnative

Troubleshooting Common Issues

• Reflection Errors in Native: Add to native-image.properties.
• Test Failures: Use @QuarkusTestTransaction for rollback.
• Performance: Profile with quarkus-micrometer.

Best Practices for Prompting Cursor

• Be specific: Mention extensions, profiles, tests.
• Iterate: Refine with "improve for native" or "add OpenTelemetry".
• Review: Always diff and commit manually.

These rules transform Cursor into a Quarkus expert companion, reducing boilerplate by 70% and boosting code quality. Apply them in your next microservice—start with cloning Quarkus Warehouse and experiment!

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