Sven Woltmann – About me

Programming has been my passion since I was eight years old. Via Basic, Turbo Pascal, Delphi, and C++, I came to Java in 1996.

My focus is on highly scalable Java backend solutions, especially on the technologies and frameworks mentioned below.

I completed my computer science studies at the TU Ilmenau in 1999 as a graduate computer scientist with distinction. I have been a member of Mensa Deutschland e. V. since 2002.

I have founded several startups, and, from 2009 to July 2019, I was a board member and CTO of AndroidPIT, the world’s largest multilingual Android community, with responsibility for the IT team with up to 15 developers and always as part of the development team.

Since August 2019, I am working as Java Backend Specialist Freelancer.

• Focused on complex problem solving and – in constant dialogue with stakeholders, with love for detail, and yet, in an adequate time – creating elegant, intuitive, efficient, scalable, secure and maintainable solutions – and then seeing how users interact with them
• Planning and implementing complex systems – and then observing how their parts and subsystems interact successfully with each other.
• The freedom to use technologies that can solve the task most efficiently – taking the macro architecture into account.
• The continuous expansion of my boundaries through new challenges and learning new technologies, principles, patterns, and practices as a result.
• Discovering how complex tasks have been solved by other developers, thereby expanding my knowledge and skills.
• Surprising other developers with new approaches to solutions, encouraging and inspiring them to create elegant, intuitive, efficient, and maintainable code themselves

• Java (Streams, Collections, Lambdas; advanced topics: Reflection, Concurrency, Performance, Java Memory Model)
• Spring Framework (Spring Boot, Spring Cloud, Spring Data)
• J2EE / Java EE / Jakarta EE / MicroProfile (Glassfish, Payara, Quarkus)
• Microservices with Spring oder MicroProfile, Kubernetes and Docker
• Relational database management systems, MySQL, JPA, Hibernate, EclipseLink
• Elasticsearch, Logstash / Filebeat, Kibana (ELK)
• Design Patterns
• Clean code (SOLID principle)
• Code quality (PMD, FindBugs / SpotBugs, Checkstyle, Sonargraph, SonarQube, SonarLint)
• Test-driven development (JUnit, TestNG, Hamcrest, Mockito, Powermock, RestAssured, Testcontainers)
• DevOps (Ansible, Jenkins, Chef)

Since August 2019:

Freelance programmer and trainer.

An extract of my current projects:

• 1&1 IONOS: Optimizing the performance of the Java-based backend for provisioning of virtual IaaS infrastructure. Technology: Java EE, Glassfish, EclipseLink, PostgreSQL. Result: Improved the performance of the provisioning logic under load by factor 50.
• 1&1 IONOS: Improving the performance of multiple REST API endpoints by up to factor 35 by optimizing code and database queries and integrating caching logic.
• 1&1 IONOS: Planning the migration to a (micro-)service-oriented architecture with Quarkus and Eclipse MicroProfile; implemented several prototypes and MVPs based on Quarkus.
• 1&1 IONOS: Planning and implementation of an API gateway and authentication service with Traefik and Quarkus.
• 1&1 IONOS: Design of the next evolutionary stage of the company-wide REST-API (“IONOS Cloud API”).
• 1&1 IONOS: Conception of the adaptation of the Java backend to enable zero downtime deployment.
• 1&1 IONOS: Converting Groovy code, as well as unit and integration tests, to Java.
• AndroidPIT: Maintaining the infrastructure and implementing features for the portal. Technologies: Java 11, Spring Framework, Spring Cloud, Spring Boot, MySQL, Elasticsearch, Kubernetes.

2009 – 2019:

• Setting up the agile IT team (Scrum) and responsibility for up to 15 employees.
• Development of a high-performance, scalable and customizable content management system for AndroidPIT since 2009 – with the Spring Framework, Hibernate ORM, Tomcat, MySQL and Elasticsearch in the backend.
• Continuous codebase upgrades from Java 6, Spring Framework 2.5 and Hibernate 3.2 in 2009 to Java 11, Spring 5.1, Spring Boot 2.1, Spring Cloud Greenwich and Hibernate 5.3 in 2019.
• Adaptation of the entire IT infrastructure to the requirements of the EU-GDPR in 2018.
• Development of the native advertising format “NEAds – Native Engagement Ads” since 2016 – implemented them as a Microservice architecture with Spring Boot, Spring Cloud, Netflix OSS, Elasticsearch and RxJava – and operated in a Kubernetes cluster.
• Development of the AndroidPIT App Center, a Google-independent app store for Android apps with various payment methods and the ability for app developers to offer discounts and promotions, – pre-installed on devices of many manufacturers in 2010.
• Development of the first web directory of Android apps in 2009 – even before the Google Play Store existed as a website – by reverse-engineering the Android App Store.
• Setting up CI/CD pipelines with Jenkins and the Jenkins Job DSL.
• Automation of the configuration and administration of the IT infrastructure with Ansible.

2004 – 2009:

Founder, board member and CTO of eleisure AG in Karlsruhe, a holding company for online gaming.

2002 – 2004:

Team leader for Windows client development at 1&1 Internet AG in Karlsruhe.

Responsible for the further development of the SMS Manager and the re-implementation of the entire SMS backbone of the United Internet Group based on Java, JMS, and JBoss (now WildFly).

2000 – 2002:

Founder, Managing Director and head of software development of W+R Software GmbH in Regensburg, developer of GMX SMS Manager, the first paid online SMS service in Germany.

Implementation of the backend with Java, JDO, Tomcat, and Oracle DB. Development of the frontend with Borland C++ Builder.

Acquisition of the company by 1&1 Internet AG in October 2002.

1999 – 2000:

Head of software development at JFAX Germany in Regensburg, the local branch of J2 Communications, provider of a Unified Messaging platform.

Setup of the German portal “jfax.de” with Java, JSP, JRun, and Oracle DB.

In August 2000, the business was handed over to the parent company in the USA.

1999:

Founder and CTO of Cleverlearn Inc., provider of an online language learning platform based in Los Angeles.

Development of the backend functionality with Java, the servlet engine JRun and Oracle DB as database system. Implementation of the frontend with Visual C++.

1994 – 1999:

Studied Computer Science at the Technical University Ilmenau with a focus on practical computer science, algorithms and data structures, and database systems.

Diploma thesis with the title “Conception, comparison, and evaluation of different approaches for the data management of an adaptive agent, based on predictive data mining” at Amazon in Seattle, USA.

I graduated as Diplom-Informatiker (corresponds to Master of Science) with distinction after nine semesters.