Sven Woltmann

When systems grow from thousands to millions (or billions) of users and transactions, they often reach their scalability limits.

Even experienced developers find it challenging to eliminate the resulting performance bottlenecks. Constant demands for new features and limited time don’t leave room for building the skills required to design architecture and code for massive growth.

This is where I have my field of expertise – as a developer and coach.

Having over two decades of experience in scalable Java enterprise applications – from monoliths to complex microservice architectures – and with a focus on advanced topics such as concurrency, reflection, the Java memory model, and garbage collection – I will support and coach your teams to push them beyond their limits.

With my background as founder and CTO of several start-ups and SMEs, I always strive to understand requirements from a business perspective. As a team lead and freelancer, I have also led and supported large corporation teams working on enterprise-level applications.

Development

• I will help you find solutions where others are stuck.
• I work with your developer teams, supporting them in solving performance and scalability issues.
• If you wish, I get a picture of your developers’ skills in pair programming and prepare coaching and training tailored to your organization.

Coaching

• I will coach your teams individually and on target.
• In one-on-one sessions or small groups, I analyze your teams’ strengths and weaknesses in light of your company’s tasks.
• Together we turn the weaknesses into strengths.
• Optionally, I prepare training courses for your entire organization.

Courses

• I will bring your employees up to date on the latest Java technology.
• Let me teach your teams how to work efficiently with streams and lambdas and how to do concurrency the right way.
• I’ll train your teams on the new language features released every six months, allowing them to code even faster.
• Choose from my course program, or let me design customized training for your teams.

Advanced Java

• New language features (switch expressions, pattern matching, sealed classes, records, virtual threads, ...)
• Streams, Lambdas
• Collections Framework incl. queues, deques, concurrent collections
• Advanced topics: Concurrency, Performance, Reflection, Java Memory Model, Garbage Collection

Scalable Enterprise Applications + Microservices

• Java EE / Jakarta EE / MicroProfile (Glassfish, Payara, Quarkus)
• Spring Framework (Spring Boot, Spring Cloud, Spring Data)
• Providing and connecting to REST APIs (+ GraphQL)
• Integration with relational database systems such as MySQL or PostgreSQL with JPA, Hibernate, Panache, EclipseLink
• CI/CD

Software Craftsmanship

• Domain-driven design
• Clean Code (SOLID principle)
• Clean / hexagonal architecture
• Test-driven development (JUnit, TestNG, AssertJ, Hamcrest, Mockito, RestAssured, WireMock, Testcontainers, Cucumber)
• Static code analysis withPMD, FindBugs / SpotBugs, Checkstyle, SonarQube / SonarCloud / SonarLint, sshgit, Trivy
• Pair + ensemble programming

• Migration of a DynamoDB database of several TB to PostgreSQL.
• Migration of the data access layer with its own DSL from DynamoDB and OpenSearch to PostgreSQL.
• Improved query performance by up to a factor of 1,000.
• Implementation of bulk updates, the updating of data, e.g. of an artist or publisher, for thousands of music works in batch.
• Fixed intertwining synchronous and asynchronous Mutiny code to make it purely asynchronous (virtual threads were unfortunately not an option).
• Consolidation of the dependencies of almost one hundred Java repositories.

• Coaching and training for scalability and performance optimization of Java EE backends and REST APIs for provisioning of virtual IaaS infrastructure.
• Under my guidance, the performance under load was improved by factor 50.
• Guided the teams conceptualizing the migration to a microservice architecture.
• Supporting the implementation of microservices with Quarkus 2.x, Java 17, and GitHub actions for build automation.
• Designed the next evolutionary stage of the company’s public REST API (”IONOS Cloud API”).
• Planned and implemented zero downtime deployment for the legacy monolith.

• Migration of the website from androidpit.com to nextpit.com.
• Adoption of the content management system to changed SEO requirements and updated third-party APIs.
• Implementing new features for the portal.
• Moving the build automation from Jenkins to GitHub Actions.

Fonpit was, as the predecessor of NextPit GmbH, the operator of the world’s largest multilingual Android community, AndroidPIT.

• Setting up the agile IT team; responsibility for 15 employees.
• Development of a highly scalable, maintainable, and customizable content management system.
• Continuous codebase upgrades 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 an advertising infrastructure as a microservice architecture with Spring Boot, Spring Cloud, Netflix OSS, Elasticsearch and RxJava, operated in a Kubernetes cluster.
• Development of the AndroidPIT App Center, a Google- independent app store with various payment options and the ability for developers to offer discounts and promotions – pre-installed on devices of many manufacturers.
• Development of the first web directory of Android apps in 2009 – before the Google Play Store existed as a website – by reverse-engineering the Android App Store.

• Development of the website and the logistics and payment backend for the game rental platform “GameAbo”.
• Development of the browser-based MMOG “Feenix – The Age of Pirates”, voted “Browser Game of the Year 2005” by 50,000 readers of the online magazine “Galaxy News”.
• Development of the backend for the browser-based 3D community “Bailamo”.

• Built a development team for various Windows projects.
• Continued development of the “GMX SMS Manager”.
• Re-implemented the entire SMS backbone of the UI Group.

• Developed the Windows application "GMX SMS Manager", the
  first paid online messaging service in Germany.
• Acquired by 1&1 Internet AG in October 2002.

Local branch of J2 Global, a unified messaging platform provider.

• Built up the German portal “jfax.de”.
• In 2000, business was handed over to the parent company.

Provider of an online language learning platform based in Los Angeles.

• Development of the Windows application “Clicktionary”
• Development of the backend software