Spring Data JPA Experts in Germany

Design and implementation of a compact ERP, CRM, accounting, and production-planning platform for a German food manufacturer. The system replaces Rechnung11, self-built Excel sheets, and manual processes for fewer than 10 internal users.

• Designed and implemented the full platform architecture as sole architect and developer.
• Built modules for customer management, B2B order handling, invoicing, production planning, and accounting support.
• Implemented DATEV export, ZUGFeRD/XRechnung e-invoicing, FinTS bank statement synchronization, and GoBD audit trail concepts.
• Used AI-supported workflows for prototyping, test support, and implementation acceleration while retaining full architecture, review, testing strategy, and technical ownership.

Technology: Java 23, Spring Boot 3, Spring Data JPA, Spring Security, Vue 3, TypeScript, PostgreSQL, Flyway, REST, OpenAPI, JWT, TOTP, RBAC, DATEV, FinTS, ZUGFeRD, XRechnung, GoBD, JUnit, Mockito, Testcontainers, Playwright, Docker, GitLab CI/CD

PLANT-MY-TREE®-per-order

The application enables Shopify merchants to automatically place tree-planting orders for every incoming order. By integrating ecological contributions directly into the purchase process, the manual effort for tracking and billing reforestation initiatives is eliminated. The system increases transparency for end customers through real-time visualizations of the ecological impact directly in the storefront. The architecture is based on a modular monolith with Spring Boot in the backend and an integrated React app inside the Shopify admin area. The solution uses webhooks to capture order data in an event-driven way and integrates the weclapp ERP system for automated monthly invoicing. An app proxy mechanism provides dynamic statistics such as CO2 compensation and planted trees without any performance loss for the merchant shop.

Tasks:

• Design of the modular software architecture based on Spring Modulith to ensure high maintainability
• Development of the event-driven business logic for evaluating Shopify orders via webhooks
• Implementation of automated invoicing by connecting the weclapp REST API
• Building the frontend using React Router and Shopify App Bridge for native integration
• Design of the database model and implementation of the persistence layer with JPA/Hibernate and Prisma
• Integration of internationalization processes for global use in the frontend and email communication
• Automation of deployment processes using Docker and GitLab CI/CD

Project skills: Java 25, Spring Boot, Spring Security, Spring Modulith, Hibernate, JPA, REST API, PostgreSQL, Maven, Liquibase, React, TypeScript, React Router, Vite, Node.js, Prisma, Zod, Docker, Docker Compose, GitLab CI/CD, Shopify CLI, Shopify App Bridge, Polaris, weclapp, i18next, Lombok, Vitest

• The goal of BIENE is to provide a uniform program for tax collection for all states.

• In tax collection, the aim is to collect the assessed taxes. This includes handling due dates, documenting incoming and outgoing payments, triggering reminders or refunds. Statute of limitations and payment reminders also play an important role. All payment transactions with banks and accounting are mapped in BIENE.

• Setting up the architecture and coordinating the provisioning of development and test environments at the Hanover location

• Installing and configuring environments on Linux servers (Apache Kafka, PostgreSQL)

• Interface tasks: coordinating and aligning the integration of software products from other departments and their test data

• Upgrading application server, JDK, Maven project structure

• Environment coordination and build management

• Implementing external interfaces

• Implementing business requirements

• Designing and implementing RESTful APIs and OpenAPI specifications

• Designing and implementing microservice architecture

• Setting up and maintaining CI/CD pipelines

• Deploying applications on OpenShift

• Creating technical documentation and diagrams

• Working with SQL databases (Oracle and PostgreSQL)

• Setting up authentication and authorization for the application and users

• Containerizing the application (automated deployment via CI/CD pipeline)

• Client: UOB Bank

• Projects: Web Server Management; Online Account Opening; Online Account Lending

• Develop and support enterprise-grade backend services for banking/insurance workflows using Java 17 and Spring Boot.

• Design REST APIs, platform integrations and backend services for customer onboarding, account workflows and lending journeys.

• Modernize legacy services into scalable microservices while improving reliability, maintainability, CI/CD and production delivery.

• Optimize PostgreSQL/MongoDB data access patterns and collaborate with Agile teams through reviews and technical guidance.

• Environment: Java 17, Spring Boot, REST APIs, Microservices, PostgreSQL, MongoDB, Docker, Jenkins, GitLab, SonarQube, Agile

(Maternity/Parental Leave: July 2023 – Aug 2024)

• Domain: Payment Domain | Client: Telefonica Germany
• Project: General Payment Service

The General Payment Service is responsible for processing of online payments via external payment service provider like Safer pay and PayPal

• Developed Design of Use (DOU) and interface contract documentation, ensuring clarity and compliance across system integrations
• Designed and delivered REST/SOAP web services with Spring Boot and Spring Data JPA, publishing Swagger contracts through WSO2 API Gateway to improve accessibility and governance.
• Spearheaded the on-premises to AWS Cloud migration, re-platforming from Oracle to PostgreSQL on AWS RDS and deploying services on EC2, improving scalability and cost efficiency.
• Containerized microservices using Docker and orchestrated deployments with Kubernetes, streamlining deployment pipelines and improving system reliability.
• Implemented proactive monitoring and logging via AWS CloudWatch and Kibana, ensuring stability and performance during cutover.
• Enhanced collaboration through code reviews and peer reviews, promoting maintainability and clean coding standards.
• Strengthened quality by writing comprehensive JUnit tests and preparing detailed test cases enabling early defect detection
• Delivered automated API testing with Ready API, Postman, and SOAPUI, and conducted performance testing with JMeter, ensuring reliability in high-transaction environments.

Project: SCS (Settlement / Clearing Services)

Settlement platform serving multiple trading and clearing venues — counterparty risk safeguarding, settlement volume reduction, central risk management, and post-trade anonymity.

Technologies: Java 17, Spring Boot 3, Microservices, Spring Data JPA, SonarQube, Fortify (SCST), Mockito, Jenkins, OpenShift, Maven, Podman, GitHub, JIRA, Liquibase, Swagger, AMQP, Apache Camel, Terraform, PostgreSQL, Instana, Graylog.

• Identified and remediated CVEs in third-party libraries using SCA tooling, strengthening the security posture of production components.
• Maintained 90% code coverage with SonarQube, improving code quality and reducing production defects.
• Enabled mTLS for database authentication and message broker connections, enforcing encrypted, certificate-validated communication.
• Designed and deployed microservices with asynchronous, REST-based communication between components.
• Optimized a high-volume REST API (~200K requests) by reducing response time from 3s to 2s (33% improvement), boosting throughput and reliability under production load.
• Automated build and continuous integration pipelines using Maven and Jenkins.
• Orchestrated containerized workloads on Podman/OpenShift and governed schema evolution with Liquibase, ensuring reliable, repeatable deployments across all environments.
• Optimized Java code and implemented EHCache-based caching, improving application performance.
• Streamlined release management by governing application images, JAR versions, and dependencies through DBAG Artifactory, ensuring version consistency and audit traceability across environments

• Contributed to the development of an advanced RAG AI Chat application that integrates multiple LLM models, enabling users to seamlessly switch between models based on specific tasks. This improved the user experience by providing tailored, efficient solutions for various use cases, such as event scheduling, booking systems, and complex task management.
• Participated in designing and implementing a robust backend architecture using Spring AI, enabling advanced AI-driven capabilities like intelligent task automation, language processing, and contextual recommendations. Leveraged Spring AI Tools and Advisors to enhance the performance and decision-making of the AI models.
• Collaborated on the integration of vector databases to support embeddings, enhancing the app's ability to understand user queries and perform actions based on complex, real-time data inputs.
• Contributed to the development of a seamless, user-friendly front-end interface using React with TypeScript support, ensuring a modern, responsive, and scalable user experience across platforms.
• Assisted in implementing state management with Redux RTK for efficient data flow and real-time updates, optimizing the overall user experience in dynamic scenarios such as scheduling and task management.
• Partnered with stakeholders to define feature requirements, helping ensure that the app could scale to meet evolving business needs and integrate with other systems like calendar and email services. Worked alongside cross-functional teams, including data scientists and UI/UX designers, to fine-tune AI models and ensure alignment with project goals.
• Contributed to ensuring end-to-end system performance, security, and compliance by helping integrate authentication mechanisms, role-based access control, and secure communication protocols in both backend and frontend layers.

Technology Stack and Key Contributions:

• Java / Spring Boot / Spring AI: Developed backend services leveraging Spring AI for intelligent responses, task automation, and complex workflows.
• React / TypeScript: Built intuitive user interfaces with React and TypeScript, ensuring a smooth and scalable frontend.
• Redux RTK: Managed application state with Redux RTK for optimized state management, enabling dynamic, real-time data updates.
• Vector Databases: Integrated vector databases (pgVector) for embedding support, improving AI model performance in handling complex queries.
• PostgreSQL / Redis: Managed persistent and temporary data with relational and in-memory data stores, ensuring data integrity and speed.
• Kafka: Utilized Apache Kafka for event-driven communication and seamless integration between microservices.
• Spring Security: Ensured the security of backend services with robust authentication and authorization mechanisms.
• CI/CD & DevOps: Integrated continuous integration and deployment pipelines to ensure rapid and secure deployment of features and updates.

• Designing and developing a web application for the public sector
• Setting up and executing software tests, mainly unit tests
• Technical design and implementation of requirements
• Uploading and displaying CSV files
• Communicating with business units regarding development and test support
• Technologies used: Java, Spring Boot, Spring Security, Spring Batch, Spring Cloud, Spring Data JPA and Hibernate, RESTful, JSON, React, Oracle, JUnit, Mockito, CI/CD, GitLab, Docker, Keycloak, Liquibase, BIRT, Swagger, Microservices

• Developed Java 21 / Spring Boot 3.2 microservices with REST and GraphQL APIs for GDPR-compliant consent workflows using Hexagonal Architecture
• Enhanced Backend-for-Frontend (BFF) performance using AI-assisted tools for code refactoring and optimization
• Built event-driven workflows with Kafka, RabbitMQ, AWS SQS, and integrated Salesforce Marketing Cloud for real-time consent tracking
• Implemented OAuth2 and Keycloak security, automated CI/CD with Jenkins, GitHub Actions, and Gradle, and deployed containerized services on Docker and Kubernetes with AWS and Azure
• Executed unit, integration, and contract testing with JUnit 5, TestNG, Mockito, and TestContainers; monitored performance via Grafana, Kibana, and AWS CloudWatch
• Developed microservices for digital identity verification and e-signature management with Hexagonal Architecture
• Integrated Keycloak 24.x with OAuth2.1 and OpenID Connect for SSO and RBAC, ensuring EU eIDAS compliance
• Designed API-first microservices with OpenAPI 3.1, Swagger, and GraphQL for improved interoperability
• Automated CI/CD pipelines with Jenkins, GitHub Actions, and Gradle; deployed containerized services on AWS EKS and Azure; monitored with Grafana, Kibana, CloudWatch, and TestContainers

• Visualization, search, and maintenance of various types of master data, providing them via a REST API, and implementing a variety of import and export formats.

• Implementation, architecture, project management.

• Technologies and tools: Angular (Signals, Signal Store, swagger-codegen, standalone components), Java, PostgreSQL, ActiveMQ, JavaScript, Spring Boot (Spring Core, Spring MVC, Spring Data/JPA via Hibernate, Spring Security, Spring Modulith), JUnit, Flyway, QueryDSL, GraphQL, REST API, Node, npm, Maven, SonarQube, GitLab CI/CD pipelines, Docker, Nexus, OpenAPI + Swagger UI, Keycloak, OAuth2, OpenID Connect, IntelliJ IDEA, Jira, Confluence.

• Backend development work for appointment and doctor services, including the implementation of various requirements for managing doctor appointments.
• SCRUM/Kanban
• Java 21
• IntelliJ Idea
• SpringBoot (MVC, Data JPA, …)
• GIT
• Confluence
• JIRA
• Maven
• CI: Jenkins
• Docker
• ActiveMQ
• MariaDB
• Solr
• Liquibase
• Testcontainer
• JUnit5
• Mockito

• Provide end-to-end software and architecture support to clients across finance, manufacturing, energy, and insurance sectors
• Collaborate with customers to understand complex business requirements and deliver scalable, future-proof solutions
• Design, implement, operate, and continuously improve software systems using modern technologies and cloud platforms
• Support the full solution lifecycle – from technical conception, system architecture, and development to deployment and operational readiness
• Act as a trusted technical advisor, bridging business and engineering teams to deliver high-impact solutions
• Lead architectural decisions with a focus on maintainability, cost-efficiency, security, and scalability across both cloud-native and on-premises environments

• Developed Skalman’s Food & Sleep Clock web app with a digital assistant that reminds users about medication intake, meals, movement breaks, and other daily routines.

• Implemented personalized meal suggestions and simple recipes with support for allergies and special diets, integrating AI to generate tailored meal ideas.

• Built Flight Booking App using React and Axios for the front end, Spring Boot with JPA and MySQL for the back end, and implemented user authentication, form validation, and booking logic.

• Designed and built a chatbot that accepts natural language queries and generates intelligent responses using OpenAI’s language model.

• Developed MarketPlace_AP with React and Axios on the front end, Spring Boot with JPA and MySQL on the back end, enabling users to discover services or products, with authentication and form validation.

• Created a Meeting Calendar page allowing users to schedule, view, and manage meetings using React, Axios, Spring Boot, JPA, MySQL, and authentication with validation.

• Created a Todo List Manager: built a REST API with Node.js, Express, and MongoDB; developed a React front end featuring status toggling and filtering; deployed on Heroku and integrated with GitHub for CI/CD.