Mid-Senior Backend Developer (Java)

At Lumen Spei, we're looking for a Senior Backend Developer (Java) to join our team and help build digital products, BSS solutions, and business applications for local and international clients. In this role, you'll also take technical ownership on projects, contribute to key architectural decisions, and support the team with your knowledge and expertise. What you'll do Develop and maintain backend applications using JavaBuild and improve digital products, BSS solutions, and business applicationsDesign and implement REST APIs and microservicesTake technical ownership of projects and contribute to architecture and technology decisionsProvide technical guidance and support to other developersCollaborate closely with frontend developers, QA engineers, Product teams, and Project ManagersIdentify technical challenges and propose practical, scalable solutionsUse modern AI tools and AI agents to accelerate software development, automate repetitive tasks, and rapidly deliver MVPsTake part in the full software development lifecycle, from idea and architecture to production What we're looking for 5+ years of backend development experienceStrong Java knowledge and solid understanding of software engineering principlesExperience designing and building production-grade backend systemsExperience working with relational databasesExperience with ORM frameworks (Hibernate, JPA, or similar)Strong understanding of REST APIs and microservice architectureExperience with Git and modern development workflowsAbility to make technical decisions and take ownership of implementationStrong communication skills and a proactive, problem-solving mindsetAbility to support and mentor less experienced developersInterest in adopting AI-powered development workflows Nice to have Experience with Spring BootExperience with software architecture and system designFamiliarity with Docker and CI/CDBasic frontend knowledge (React is a plus)Experience with JiraLinux environment experienceExperience using AI coding assistants or AI-powered development tools What we offer The opportunity to work on modern digital products, BSS solutions, and long-term projectsThe opportunity to take technical ownership and have a real impact on architecture and project deliveryA development environment that embraces AI-assisted software engineeringProject Management Office and a team that helps you deliverHybrid work model in OsijekFull-time positionEmployment or B2B cooperation (contract or your own business/company)Competitive salaryPaid certifications and professional developmentEquipment of your choiceRegular performance reviews and career growth opportunities Location Osijek, Croatia (Hybrid) How to apply Send us your CV and GitHub profile to info@lumenspei.com with the subject: "Senior Backend role - Lumen Spei Osijek" by the end of September 2026.