Sabahattin K.-Senior Java Developer | Lead Developer | Architect | Team Lead
Check rate
Experience
Sole responsibility (design, development, infrastructure, operations)
Own project busik.ch
- Ride-sharing and bus platform, live and fully functional. Backend with Spring Boot 4.1 on Java 21, PostgreSQL with Flyway, and Testcontainers integration tests. Hosted in my own AWS account (ECS Fargate, ALB, ECR, IAM Least-Privilege) with CI/CD via GitHub Actions and OIDC federation without static credentials. Development fully AI-supported with Claude Code, including custom skills and project-specific memory. Spring Boot · Java 21 · PostgreSQL · Flyway · Docker · AWS ECS/ALB/ECR · CI/CD · GitHub Actions · Claude Code
Backend, frontend & IoT integration software developer
Pars Scooter
- Kotlin backend based on Spring, modularly structured, for an e-scooter sharing platform (fleet of over 1,000 vehicles, 24/7 operation); deployment and container management via Portainer. Kotlin · Spring · Portainer · REST · GraphQL · MongoDB
- Integration of IoT devices in C and C++ for vehicle communication across the e-scooter fleet.
- Frontend in Flutter — delivered in 2025 as native Android and iOS apps (Google Play Store and Apple App Store). Mapping of the business processes registration, reservation, rental, and fleet management.
Full-stack developer
Swisslife
Role: Senior Developer, Architecture, Lead Developer
Senior Developer: Monolith → REST architecture Redesign of several EJB monoliths into scalable REST services. Architecture, schema, and framework decisions (OpenAPI, Flyway, Camunda) while retaining the legacy interfaces. OpenAPI · Camunda · Flyway · EJB → REST
Senior Developer: New development of InvestEasy Financial planning advisory software (2nd/3rd pillar) in accordance with Swiss regulations: tax domicile, source of funds, beneficiaries, citizenship. Fund selection based on risk profiling. Spring Boot · Quarkus · React · TWIN signature · Video identification · OpenAPI · Camunda
Team Lead: Redesign of mortgage financing Migration from EJB to microservices with direct REST calls for external partners (previously: email). Reduction of incidents from ~100 to 2–5 per week through the Visitor pattern and type-safe data validation in pure Java. REST · Microservices · Design Patterns · Clean Code
Developer / Architecture: Partner portal – Lead Developer & Operations (approx. 2,400 active users) Sole responsibility for the further development and operation of the broker platform (commissions, employee management, customer master data). Liferay migration to 2026.Q1, OneLogin OIDC, React frontend rebuild, Azure DevOps pipeline, and AI-supported development with Claude Code CLI. Ensuring maintenance cycles. Liferay · OSGI · React · TypeScript · Azure DevOps · OIDC · Claude Code · 2026.Q1
Skills: Java 17/21, CDI, React, JSF, T-SQL, PrimeFaces, OmniFaces, Shell script, OSGI, Felix, REST, OpenAPI, GraphQL, Python, TDD, unit testing, Clean Code, Docker, Quarkus, SQL, SMTP, WSDL, DevOps, XML, Bourne-again shell, bash, Z shell
Products used: IntelliJ, WildFly, Linux, CSS3, Docker, Elastic Search, Spring Core, Kubernetes, Argo CD, Git, GitHub, Azure, Apache Lucene, Docker Compose, Camunda, OSGI, MS SQL Server, REST, HTML5, JavaScript, OpenAPI 3, Spring, Spring Batch, Liferay, Azure DevOps, ELK, Kibana, Ehcache, SonarQube, SSL, ConfigSeeder, Bash, Shell script
Senior Developer
SIX
Role: Senior Developer, Supporting other Developers
Senior Developer: Refactoring legacy Java code from EJB to REST microservices for improved scalability and maintainability.
Senior Developer / DevOps: Maintenance and design of Spring Boot and Docker components to achieve resilience through a cluster using the Blue Green pattern.
Senior Developer: Conversion of a single persistence layer into a multi-persistence layer in legacy code. Implementation of integration tests and a verification layer to ensure transaction safety across all levels. Design of rollback scenarios to ensure transaction safety.
Senior Developer: Design and setup of a persistence layer for search indexes using Elasticsearch, and modeling of performance-optimized search indexes to enable search that was not available in a NoSQL database. Data synchronization from NoSQL to Elasticsearch – implementation of a performance-optimized search: increased result delivery speed by more than 500%.
Senior Developer: Monitoring and guidance of new developers (mostly external) regarding code quality and verification of requirements against the code.
Senior Developer: Performance optimization and refactoring of legacy Spring Batch code (production and testing) to improve speed and maintainability.
Senior Developer: Solving the generic financial product challenge – implementation of a generic UX component in TypeScript and React.
Development / DevOps: Release management – rollout of new components using Docker and Kubernetes.
Skills: Scrum, Design Patterns, Java API, REST Services, Clean Code, DevOps, TDD, Lucene, SQL, PL/SQL
Products used: JetBrains IntelliJ IDEA, Docker, Docker Compose, Jenkins, CI/CD, Oracle, OracleNoSQL, MySQL 5, JPA, Mockito, ReactJS, JSON, Enterprise Architect, Confluence, JIRA, Bitbucket, Git, FindBugs, SonarQube, WSDL, REST
Lead Developer
Employment Agency
- Lead Developer: Implementation of a content and metadata search based on microservices, Angular (frontend), and Elasticsearch and Lucene indexes. Implemented with Java 8 / Spring. Modeling of search indexes with analyzers and non-persistent fields.
- Development: Frontend and backend.
- Architecture: Setup and operation of a Docker cluster, DC/OS Mesos for orchestration and scaling of the microservice components.
Skills: Scrum, Clean Code, TDD
Products used: Eclipse, IntelliJ IDEA, Elastic Search, Storm Crawler, bash, Docker, DCOS Mesos, Webstorm, Spring 4.1, Apache Lucene, Spring Boot, FeignClient, OkHttp Client, Mockito, MockMvc, Bash Shell, Design Patterns, AngularJS, JIRA, Confluence, Git, Java API, REST Services, REST, FindBugs, Angular, Kotlin
J2EE Software Developer / Architect
Energy Utility (Switzerland)
Software development and quality control, as well as code reviews of software deliveries. Set up Continuous Delivery using JBoss RHQ. Split delivery packages into microservice-ready building blocks. Connected control, monitoring, and regulation systems in the energy sector. Bug fixes (J2EE backend, Spring, JSF/PrimeFaces frontend, AngularJS). Migrated various projects from JDK 7 to JDK 8.
- Development: Connected different systems through backend/frontend data synchronization.
- Development: Transferred archive data to the eArchive.
- Development: Developed a business object registry for the object cardinality of the different systems.
- Development: Bug fixing, integration tests, and unit tests.
- Architecture: Replaced an Apache Camel project with Camunda BPMN, improving maintainability and process visibility.
- Development: Extended existing projects with a Kerberos authentication service.
- DevOps: Built JBoss templates with Docker and Vagrant.
Skills: Scrum, Agile, Reengineering, DevOps
Technologies used: OData, JSF, PrimeFaces, AngularJS, Java 8, Camunda BPM, Spring 3.0, Spring Batch, Spring Data, Feign REST Client, Quartz Scheduler, JBoss, WildFly, Git, ElasticSearch, Apache Lucene, Spring Boot, SonarQube, J2EE, JPA, JAXB, Oracle, H2, CSS, Kotlin
Developer / Team Lead (Backend/GUI)
UniCredit Bank
Team Lead: Implemented a user interface for reconciling master data in the areas of group partners, clients, partners, and affiliated companies (debt reporting to the German Federal Bank).
Tools: JBOSS 6.3 GA, Java 7, Eclipse, EJB 6, JPA, Mockito, JUnit, CDI, Jenkins, HTML, CSS, Hibernate, PrimeFaces 5.2, JSF 2.2, Activiti BPMN Engine, Apache Lucene, Batch JSR 352, JAX-WS, JAXP, REST, SOAP, Apache ActiveMQ, SonarQube, FindBugs, Maven, PowerMock, XStream
Skills: Scrum, TDD, Agile development, Change Request Management
Technologies used: Atlassian Confluence, JBoss, Java 7, J2EE, JPA, Mockito, CDI, HTML5, Hibernate, PrimeFaces, JSF, Activiti, SOAP, SoapUI, JAXB, JUnit, PowerMock, Apache Lucene, SonarQube, WSDL, ActiveMQ, BPMN, FindBugs, Kotlin, Spring Batch
Head of Software Cytology Systems
amedes Medical Services
- Team size / customers: 8 people / 20 company-owned laboratories / 60 external competitor laboratories
After acquiring a laboratory software product, amedes medical services needed someone capable of moving the software to a new architecture, ensuring operations including the software certification required in Germany (every two years), and reassuring competitor companies that no data would leave the department. The goal was to ensure smooth continued operation. After this period, the software was sold at a profit to a software group.
- Management: Disciplinary responsibility for a team of software developers: team leadership, setting objectives, performance reviews, and career development for team members.
- Management: Project responsibility: planning, managing, and monitoring software projects regarding deadlines, quality, and resource use.
- Management: Budget and cost control: total budget of €2 million (personnel and hardware) – preparing and monitoring project budgets, resource and effort estimates, and coordinating with management.
- Management: Rolled out the software to all laboratories (MOLIS and cytology) without operational interruptions – including planning, training, and onboarding the laboratory doctors and laboratory assistants who joined the company.
- Management: Led and coordinated a steering committee with doctors and laboratories for requirements gathering, project implementation, and acceptance after the business was acquired by the amedes group.
- Architecture: Decision-maker with responsibility for software strategy, hardware, and architecture (software and hardware).
- Organization: Responsible for the introduction and operation of the software, including KBV certification, as well as quarterly billing to the KBV across Germany for around 80 laboratories.
Technologies used: MS-Project, Omnis7, Oracle 10g, PostgreSQL
J2EE Software Developer / Team Lead / Test-Driven Development
Shipping Company (International Project)
- Team size: 6 people
Goal: Implemented a logistics application to replace 60 isolated solutions. Project language: English (meetings, specifications, negotiations, nearshore teams). Designed and developed the frontend in JSF and the service layer/backend in J2EE, as well as batch processing for tariff management and central systems. Modeled processes with Activiti in various modules. Responsible for implementing workflow processes and analyzing requirements. Distributed application for around 2,500 users in cluster operation, synchronization processes, asynchronous processes, batch process management, performance analysis, and optimization.
Skills: TDD, Scrum, Clean Code
Technologies used: Eclipse, Icefaces, TIBCO, ActiveMQ, Gradle, Git, Jenkins, Maven, Activiti BPMN, Camunda, XSLT, XML, AltovaXMLSpy, CDI, JSF, JSFUnit, JasperReport, Mockito, PowerMock, EclipseLink, Hibernate, JUnit, Oracle 11, JPA
Project Manager / Deputy Head of Development with Personnel Responsibility
HHLA Hamburg Port Consulting
- Team size: 7 people
Managed an existing ERP software system in the Port of Hamburg and at four additional terminals in Poland (order volume approx. €800,000 per year). Built and standardized missing system communication. Created a web portal for online orders and container tracking. Negotiated and concluded an SLA and migration project with the customer. Started the project as a freelance employee and was later hired permanently.
Technologies used: Java, JSF, JBoss Portal 2.7/JBoss 5, Maven, Uniface 8.3.4, JMS, J2EE, EJB3, Swing GUI, JUnit, SQL, PL/SQL, XML, XSLT, Hibernate, Spring, Subversion, Eclipse
Technology Consultant and Developer
Municipal Data Processing
- History tracking: Certification-compliant change log for all software products – traceable display of data changes (including n:m relationships) for non-IT users.
- Journal management: Company-wide and cross-product journal management based on history tracking.
- JASPER reporting integration: Integration of the open-source reporting tool with UNIFACE (4GL call-out) via JNI through C++ to Java.
- Ordering dialog: Replacement of a native GUI with a web GUI (multi-tier architecture with web service and loose coupling).
Products used: Microsoft Visual Studio 2005, UNIFACE 8, Eclipse, Subversion, Enterprise Architect, Oracle, SQL Server, C++, PL/SQL, TSQL, JSP, JSF, JBoss, J2EE, EJB2, Tomcat 5, Maven 2, Java 6, JNI, JMS, JUnit
Developer, Technology Consultant
Laboratory Services
Developer: Development of C# software for monitoring laboratory orders by urgency and priority (layout based on the information board/airport principle).
- Implementation of an in-house data warehouse reporting tool solution: DB export to Excel using XML and C#
- High-performance image server/client: Display of scanned orders (TIFF, multi-page) in remote desktop operation via WCF/socket connection
Products used: C# frontend/backend, sockets, services, PL/SQL, Microsoft Visual Studio 2005, SQL Server, WCF, .NET, ADO.NET (part-time project)
Analyst and Implementer
DevOps: Relocation of a computer node in the data center from an HPUX cluster to several nodes with openSUSE Enterprise Edition. Analysis and migration of ~36,000 Java batch and 3-tier classes (Swing + web). Setup of a test environment, mass testing, and feasibility analyses. Integration into the production schedule without any visible interruption for external users.
Products used: C, C++, MFC, JNLP, JNI, bash, kshell, Java, J2EE, EJB2, Swing GUI, JBoss 4, make, SQL, TSQL, XML, XSLT, ANT, Maven, Subversion
Developer, Team Lead
Logistics (Hamburg / Frankfurt)
Developer/Team Lead: New customer project – development in Uniface for transporting containers in Germany. Communication with various external systems. Project size: ~15 people + the customer's IT department. Team lead for: sales conditions, web integration of external partners, web price information system, customer billing, quotation management, complaints management. Integration of external road and rail networks via web service.
Products used: Uniface 8.4.x, Java, EJB, JUnit, JSP, Servlet, Tomcat 5.x, XML, DTD, XSL, SQL Oracle, JNDI, UML, JMS, WSDL, C++, UNIFACE Application Server, Scriptura, Eclipse, XMLSpy, Oracle 9.x
Industry experience
See where this freelancer has spent most of their professional time.
Experienced in Information Technology, Banking and Finance, Transportation, Insurance, Healthcare, and Government and Administration.
Business area experience
See which departments and functions this freelancer has contributed to most.
Experienced in Information Technology, Product Development, Project Management, Investments and M&A, Quality Assurance, and Operations.
Summary
I read the job posting for the modernization of a Java-based application for loan processing in the core banking environment with great interest. I have already successfully completed exactly this task: converting a legacy loan process to a modern microservices architecture.
At Swiss Life, I migrated mortgage financing from EJB to microservices, with direct REST interfaces to external partners instead of manual email processes, reducing the incident rate from around 100 to 2 to 5 per week. I have a total of nine years of experience in the Swiss financial sector, including seven years as an architect and lead developer at Swiss Life, redesigning several EJB monoliths into scalable REST services, including schema and framework decisions.
Java, Spring Boot, microservices, and REST APIs are my daily tools, as is PostgreSQL: my own project busik.ch runs with PostgreSQL and Flyway. I designed, developed, and operate it independently, including CI/CD via GitHub Actions with OIDC federation without static credentials, running in my own AWS account. Test automation (JUnit, Mockito, Testcontainers) and cloud migration (Kubernetes, Azure AKS) are just as much part of my standard toolkit as code reviews and a strong focus on code quality.
AI-supported development is part of my daily practice: busik.ch was developed entirely with Claude Code, including custom skills and project-specific memory in the repository. At Swiss Life, I also connected an MCP server and automated recurring tasks with custom Copilot skills.
I am available for the project from 15 September 2026 and am flexible regarding the remote share with occasional on-site presence in Frankfurt. I look forward to being introduced to the client and to a conversation.
Skills
Java
Architecture
Pl
Frameworks / Middleware: Spring Boot, Spring Batch, Quarkus, J2ee/Ejb, Cdi, Osgi, Jsf/Primefaces, Icefaces, Activiti Bpmn, Camunda, Apache Camel, Hibernate, Jpa, Openapi, Graphql, Jakarta Ee, Enterprise Beans
Frontend: React, Angular, Typescript, Jsf, Html5, Css3, Freemarker, Gwt
Search & Data: Elasticsearch, Apache Lucene, Kafka, Activemq, Tibco, Jdbc, Odata
Devops / Cloud: Docker, Kubernetes, Argo Cd, Azure Devops, Jenkins, Github, Git, Sonarqube, Shell Script
Databases: Oracle, Postgresql, Mysql, Ms Sql Server, H2, Oraclenosql, Mongodb, Redis
Programming Languages: Java 8/17/21 (+++), Kotlin, Typescript, Python, C++, C#, Bash/Kshell
Operating Systems: Linux, Macos, Unix, Windows
Methods: Scrum +++, Tdd +++, Clean Code ++, Design Patterns ++, Domain-Driven Design +, Pair Programming
Version Control: Git +++, Subversion ++, Clearcase ++
Application Server: Jboss 4/5/6/7 +++, Wildfly 10 +++, Glassfish 4 ++, Apache Tomcat +++
Test Frameworks: Junit +++, Mockito +++, Mockmvc +++, Powermock +, Arquillian +++
Build Tools: Maven Including Nexus +++, Gradle +, Ant ++
Mobile: Android ++, Ios ++
Ai / Automation: Claude Code Cli, Ai-Supported Development, Agentic Ai Squad
Languages
Education
University of Applied Sciences for Business
Diploma in Computer Science (University of Applied Sciences) · Business Information Systems · Paderborn, Germany
University of Applied Sciences for Computer Science
Computer Science Assistant · Programming and Robot Programming · Siegen, Germany
Statistics
Experience
Global experience
Expertise
Qualifications
Profile
Frequently asked questions
Have questions? Find more information here.
Sabahattin is based in Diedorf, Germany and can operate in on-site, hybrid, and remote work models.
Sabahattin speaks the following languages: German (Native), Turkish (Native), English (Advanced).
Sabahattin has at least 23 years of experience. During this time, Sabahattin has worked in at least 14 different roles and for 13 different companies. The average length of individual experience is 2 years and 7 months. Note that Sabahattin may not have shared all experience and actually has more experience.
Based on recent experience, Sabahattin would be well-suited for roles such as: Sole responsibility (design, development, infrastructure, operations), Backend, frontend & IoT integration software developer, Full-stack developer.
Sabahattin's most recent position is Sole responsibility (design, development, infrastructure, operations) at Own project busik.ch.
In recent years, Sabahattin has worked for Own project busik.ch, Pars Scooter, and Swisslife.
Sabahattin is most experienced in industries like Information Technology, Banking and Finance, and Transportation. Sabahattin also has some experience in Insurance, Healthcare, and Energy.
Sabahattin is most experienced in business areas like Information Technology, Product Development, and Project Management. Sabahattin also has some experience in Investments and M&A, Quality Assurance, and Operations.
Sabahattin has recently worked in industries like Information Technology, Banking and Finance, and Insurance.
Sabahattin has recently worked in business areas like Information Technology, Product Development, and Investments and M&A.
Sabahattin holds a Bachelor in Business Information Systems from University of Applied Sciences for Business.
Sabahattin will be available full-time from October 2026.
Daily rate distribution
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Average rates for similar positions
Rates are based on recent contracts and do not include FRATCH margin.
The average daily rate is the mean of all daily rates from recent contracts of comparable freelancers on our platform.
The median daily rate is the middle value of all daily rates — half of comparable freelancers charge less, half charge more. Unlike the average, it is barely affected by outliers.
Calculated based on our freelancers’ daily rates as of 16 Sep 2026. Actual rates may vary depending on seniority level, experience, skill specialization, project complexity, and engagement length.
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