Senior Java Software Engineer

Senior Java Software Engineer – Luxembourg Location: Luxembourg – Primarily Onsite Contract: Freelance Duration: 220 days Assignment Period: 01/10/2026 – 27/09/2027 Seniority: Senior – 7+ years of experience Remote: Up to 40%, subject to onsite availability at short notice About the Role We are looking for a Senior Java Software Engineer to join a large-scale institutional environment and contribute to the development, enhancement and support of business-critical backend applications. The role is highly hands-on while also requiring technical ownership, design leadership and mentoring responsibilities. You will work closely with Solution Architects, Business Analysts, QA and DevOps teams to deliver secure, scalable and maintainable solutions. Key Responsibilities Design, develop and maintain backend applications using Java 17 and Spring Boot.Design and implement REST APIs and scalable application components.Develop persistence layers using JPA/Hibernate.Work extensively with SQL and relational databases.Translate complex functional and technical requirements into robust solutions.Lead technical design and contribute to architectural decisions.Conduct code and design reviews and promote development best practices.Mentor and provide technical guidance to other Java developers.Develop automated tests using JUnit and ensure appropriate test coverage.Design and maintain integrations using Apache Kafka or equivalent messaging technologies.Contribute to asynchronous and event-driven architectures.Work with Maven, Git and CI/CD pipelines.Collaborate with DevOps teams on build, deployment and release activities.Provide 2nd-line production support, troubleshoot complex incidents and perform root-cause analysis.Identify opportunities to improve application quality, performance, reliability and maintainability.Document technical solutions and contribute to knowledge transfer. Mandatory Technical Skills Java 17Spring Framework / Spring BootJPA / HibernateSQL and relational databasesREST API developmentApache Kafka or equivalent messaging technologyJUnit / automated testingMavenGitCI/CD pipelinesCore Competencies Strong Java backend development expertise.Excellent object-oriented programming and software engineering principles.Experience designing robust, scalable and secure backend architectures.Strong experience with RESTful services and enterprise applications.Good understanding of asynchronous messaging and event-driven architectures.Strong analytical and problem-solving capabilities.Experience with code reviews and development standards.Ability to take ownership of technical decisions.Proven experience mentoring or coordinating developers.Strong troubleshooting and production-support capabilities.Excellent communication and collaboration skills.Strong focus on software quality, security, performance and maintainability. Nice to Have Banking or financial-services experience.Azure DevOps.Liquibase.SOAP web services.Experience within European institutions.Experience developing business-critical or financial applications.Experience in complex institutional environments.Agile or structured software delivery experience.Previous experience with 2nd-line production support. Working Arrangement The assignment is primarily onsite in Luxembourg. Teleworking may be authorised on agreed days, up to 40% of the envisaged onsite presence. Candidates must be able to attend the premises at short notice, potentially within 24 hours, when required.