11/13/2026 updated
verified
Premium member
100 % availableSenior Java Developer / Consultant
Zabok, Croatia
Germany +2
Ms.Sc. Computer Science (diploma engineer), Faculty of Electrical Engineering and Computing, Zagrebinfo: Germany, Austria, Switzerland
About me
Senior backend engineer, architect and tech lead with 20+ years in Java, Spring Boot and Kotlin microservices. Currently leading the backend of a multi-tenant healthcare SaaS on AWS. Known for zero-downtime migrations and solving hard production problems. Healthcare, fintech, telecom, energy.
Web InterfacesJava (Programming Language)XML SchemaSpring SecurityApache ActiveMQApache TomcatCode ReviewDatabasesContinuous IntegrationDB2 SQLSoftware Design PatternsLinuxGradleGrails (Framework)Hibernate
Languages & Runtimes: Java (J2SE 1.4 / 1.5 → Java 21 / 25), Kotlin, Groovy, SQL, JavaScript, Scala
Frameworks: Spring Boot 3 / 4, Spring Security, Spring Data JPA, Spring Cloud Gateway, WebFlux, Hibernate, Java EE / EJB, Camunda BPM, Apache CXF, Grails, Axon
Architecture: Microservices, Multi-tenancy, Domain-Driven Design, Event-Driven Architecture, SOA, REST, OpenAPI / contract-first, RFC 9457, Design Patterns, UML, Data Modeling
Security & Identity: Keycloak (incl. custom SPI extensions), OAuth2 / OIDC / JWT, RBAC, PKI / X.509, EJBCA, Certificate Transparency, eIDAS, TLS / SSL, SmartCard PKI
Cloud & Infrastructure: AWS (ECS Fargate, ALB, SQS, S3, WAF, CloudFormation), OpenShift, Kubernetes, Docker, WebSphere Liberty / AS, Tomcat, Jetty, JBoss, Linux
Data & Messaging: MySQL, PostgreSQL, Oracle, IBM DB2, MongoDB, Redis, Caffeine, HikariCP, Apache Kafka, ActiveMQ / JMS, IBM WebSphere MQ
Quality & Delivery: Testcontainers, JUnit, Spock, ArchUnit, SonarQube, MapStruct, OpenTelemetry, JFR / async-profiler, GitLab CI, Jenkins, Maven, Gradle, Git
AI-assisted Engineering: Claude Code (custom skills & subagents), MCP integrations, LLM API integration, prompt engineering, machine-readable engineering standards
Leadership: Technical leadership, architecture ownership, code review, mentoring, refinement & technical grooming, stakeholder communication
Experience
Professional experience10+ years
Freelancer since2016
Languages
GermanBasic knowledgeEnglishFluentCroatianNative speaker
Project history
Greenfield rebuild of a legacy Delphi pediatric EHR into a multi-tenant Spring Boot microservice platform on AWS, coexisting in production with the legacy desktop client. Backend technical lead: designed and built the shared platform library every service inherits - database-per-tenant routing with lazy and cached connection, JWT resource-server security with RBAC derived from the legacy permission catalog, tenant-local datetime handling, legacy-compatible audit trail, event publishing for desktop coexistence, RFC 9457 problem details, safe pagination/sort parsing and deadlock-resilience primitives. Bootstrapped domain services from a common contract-first template. Built the Kotlin BFF/gateway authentication and session layer (Keycloak multi-realm, single active session, inactivity timeout with heartbeat, SSE pass-through, multi-location login) and a Keycloak Event Listener SPI. Root-caused and fixed intermittent production MySQL deadlocks and turned the fix into a fleet-wide prevention standard; enforced architecture as ArchUnit tests and acceptance-criteria e2e suites. AI-assisted engineering: runs day-to-day delivery through Claude, with the project’s engineering standards and the ticket lifecycle itself written down as machine-readable rules and custom skills - refinement verified against legacy sources, implementation in vertical slices delegated to specialised subagents. Ticket refinement and technical grooming, technical sign-off reviews, code review and mentoring.
Implementation of new Croatian Automated Import System (CCI – centralised customs) project for Croatian Customs. Technical leadership, proof-of-concept solutions, integration with external system, Implementation of integration modules for CCN2 (EU inter-member-state message exchange) and bookkeeping system (NIK), code review, mentoring, supported developers. Implemented also integration with Tariff system, implementation of national rules validation modules, implementation of various business process use-cases. Support DevOps and testers.
Built a custom SOAP API Gateway with security transformation & termination features for government customs administration. I was sole designer & developer of a PoC and, after evaluation, the full-featured solution. Refactored the solution to support OpenShift deploment, application deployment containerization and configuration simplification.