Senior Java Developer (AWS/RxJava) en Spain, Castro

We are still looking for the very Top Talent…and we would be delighted if you were to join our team!

More in detail, UST is a multinational company based in North America, certified as a Top Employer and Great Place to Work company with over 35,000 employees worldwide and presence in more than 35 countries. We are leaders in digital technology services, providing large-scale technological solutions to some of the world's most renowned organizations.

What we look for?

We are seeking a highly skilled Senior Java Developer with extensive experience building scalable, high-performance distributed systems.

You will join a talented engineering team responsible for designing, developing, and evolving mission-critical applications using modern Java, cloud-native architectures, and event-driven technologies.

⚙ Key Responsibilities:

• Design, develop, and maintain robust backend services using Java 17/21 and Spring Boot.
• Build scalable and resilient microservices leveraging reactive programming principles.
• Develop and maintain gRPC APIs and Protobuf schemas, ensuring backward compatibility and proper schema evolution.
• Implement highly concurrent and performant solutions, applying advanced thread-safety and concurrency patterns.
• Work with Kafka-based event-driven architectures and production-scale data stores.
• Create and maintain automated testing suites, including unit, integration, and contract tests.
• Collaborate with cross-functional teams on architecture decisions, design reviews, and technical documentation.
• Participate in troubleshooting, root cause analysis, and postmortem activities.
• Contribute to CI/CD pipelines, cloud infrastructure, and containerized deployments.
• Produce clear technical documentation, design proposals, and pull request descriptions.

Mandatory Requirements:

• 8+ years of professional experience with Java development.
• 3+ years of hands-on experience with Java 17 or Java 21, including modern language features such as records, sealed classes, pattern matching, and virtual threads when applicable.
• Strong expertise in Spring Framework and Spring Boot in production environments.
• Proven experience with reactive programming using Project Reactor or RxJava (Mono, Flux, backpressure, retry strategies, hot vs. cold publishers), or advanced asynchronous programming with CompletableFuture and structured concurrency.
• Production experience with gRPC and Protocol Buffers, including streaming RPCs, deadlines, interceptors, and schema evolution.
• Strong understanding of concurrency fundamentals, executor services, lock-free patterns, and thread lifecycle management.
• Solid testing practices using JUnit 5, Mockito, and AssertJ.
• Experience developing integration tests against real dependencies and contract/parity testing.
• Strong knowledge of Kafka consumer and producer semantics.
• Production experience with at least one of the following technologies: Redis, PostgreSQL, or MongoDB.
• Cloud experience with AWS (or equivalent cloud platforms), including services such as S3, IAM, managed Kafka solutions, and container runtimes.
• Excellent written communication skills with the ability to create design documents, postmortems, and technical documentation.
• English level C1 or higher.

Nice to Have:

• Experience leading large-scale migrations or refactoring initiatives across multi-module codebases.
• Knowledge of container packaging and multi-architecture image builds (Linux/AMD64 and Linux/ARM64).
• Python knowledge with the ability to read, understand, and debug existing code.
• Experience working with Apache Arrow or other columnar data formats.
• CI/CD pipeline ownership using TeamCity, GitHub Actions, or similar technologies.
• Experience contributing to architecture and technical strategy discussions.

What can we offer?

• ✈️ 23 days of Annual Leave plus the 24th and 31st of December as discretionary days!
• ❤️ Numerous benefits (Health Care Plan, Internet Connectivity, Life and Accident Insurances).
• Flexible Compensation Program: meals, kindergarten, transport, online English lessons, health care plan, and more.
• Free access to several training platforms.
• Professional stability and personalized career development plans.
• Referral Program with attractive bonuses for successful recommendations.
• The option to choose between 12 or 14 salary payments per year.
• Real Work-Life Balance measures (flexibility, remote work policy, summer schedule, and more).
• Access to UST Club discounts and gym membership benefits.

If you would like to know more, do not hesitate to apply and we'll get in touch to share all the details. UST is waiting for you!

At UST, we are committed to equal opportunities throughout our recruitment processes and do not discriminate based on race, gender, disability, age, religion, sexual orientation, or nationality. We have a special commitment to Disability & Inclusion and actively encourage applications from professionals with a disability certificate.