Senior Java Backend Developer

Java 17/21 · Spring Boot · Reactive Programming · gRPC · Protobuf · Kafka · AWS

• 8+ years of professional experience with Java.
• 3+ years working with Java 17 or 21, including records, sealed types, pattern matching, and virtual threads where appropriate.
• Deep experience with Spring / Spring Boot in production services.
• Experience in reactive programming with Project Reactor or RxJava: Mono/Flux, backpressure, retry/backoff, and hot/cold publishers.
• Alternatively, solid experience in asynchronous programming with CompletableFuture and structured concurrency.
• Production experience with gRPC and Protobuf, including streaming RPCs, deadlines, interceptors, and schema evolution.
• Solid knowledge of concurrency: thread-safety, executor sizing, lock-free patterns, and lifecycle management of long-running processes/threads.
• JUnit 5, Mockito, and AssertJ.
• Integration tests against real dependencies.
• Experience with contract testing and parity testing.
• Commitment to best practices for code quality and maintainability.
• Experience with Kafka, both in consumption and production, and its different semantics.
• Production experience with at least one of these technologies: Redis, PostgreSQL, or MongoDB.
• Solid knowledge of AWS or equivalent cloud, especially:
• S3
• IAM
• Managed Kafka
• Container runtimes
• Excellent written communication skills.
• Ability to produce clear and useful technical design documents, postmortems, and Pull Request descriptions.
• Ability to work autonomously and collaborate with technical teams.

• Having led relevant migrations or refactorings in codebases with multiple modules.
• Experience in container packaging and building multi-architecture images (linux/amd64 and linux/arm64).
• Knowledge of Python, with the ability to read and debug code when necessary.
• Experience with Apache Arrow or columnar data formats.
• Experience in ownership of CI/CD pipelines with TeamCity, GitHub Actions, or equivalent technologies.

English level: C1 mandatory.

AD4 Octógono is looking for a Senior Java Backend Developer to join a technological project where experience in modern Java, concurrent programming, distributed services, and cloud architectures will be key.

We are looking for a technically solid profile, capable of working autonomously, making design decisions, and participating in the evolution and modernization of high-demand backend services.

• Location: Madrid or Andalusia (Málaga, Sevilla, Córdoba, Jaén). Remote possibility for highly qualified profiles.
• Working Day: 40h from September to June and 35h during the months of July and August.
• Salary: €40,000 - €47,000 depending on knowledge and experience provided.

• High technical and analytical capacity.
• Autonomy and responsibility.
• Ability to tackle complex problems.
• Orientation towards quality and best practices.
• Clear technical communication.
• Teamwork.