Sven Woltmann

I am a Java Scalability and Performance Specialist with 20+ years of professional experience in designing, implementing, and optimizing high-performance, scalable, and maintainable Java backend systems based on Spring or Jakarta EE.

I help development teams build efficient architectures, analyze and resolve performance bottlenecks, and apply Clean Code principles – ensuring that their applications scale reliably while remaining well-structured and easy to maintain.

How I Can Help:

• Architectural Design & Implementation:
  Designing and optimizing Java backend solutions for performance, scalability, and maintainability.
• Performance & Scalability Tuning:
  Identifying and resolving performance bottlenecks using deep expertise in concurrency, memory management, garbage collection, and JVM internals.
• Development Support & Coaching:
  Helping teams refine their coding practices, troubleshoot complex issues, and apply Clean Code principles for maintainable and future-proof software.
• Training & Workshops:
  Delivering customized courses on Java performance tuning, modern language features, and best practices to keep teams up to date with the latest advancements.

My Background:

Having worked with engineering teams as a founder, CTO, and consultant, I combine technical expertise with a business mindset.

My work spans designing and implementing complex enterprise solutions from scratch, leading monolith-to-microservice transitions, and optimizing large-scale applications for performance and scalability.

I regularly share my knowledge on HappyCoders.eu and as a speaker at Java User Groups (JUGs) and conferences. You can find an overview of my past talks here.

Advanced Java

• Modern Java language features (switch expressions, pattern matching, sealed classes, records, virtual threads, structured concurrency, scoped values, stream gatherers, ...)
• Streams, Lambdas
• Java Collections Framework with its lists, maps, queues, deques, and concurrent collections
• Advanced topics: concurrency, performance, reflection, Java Memory Model, garbage collection, heap dump analyzes

Scalable Backend Solutions, Microservices, Cloud

• Spring Framework (Spring Boot, Spring REST, Spring Data, Spring Cloud)
• Java EE / Jakarta EE / MicroProfile (Glassfish, Payara, Quarkus)
• Providing and connecting to REST APIs (+ GraphQL)
• Integration with relational database systems such as MySQL or PostgreSQL with JPA, Hibernate, Panache, EclipseLink
• Integration with NoSQL systems such as Firestore, DynamoDB, or ElasticSearch
• Amazon Web Services (AWS), Google Cloud Platform (GCP)

Software Craftsmanship,
Software Architecture

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

As the Founder and Author of HappyCoders.eu, I have built a platform to support and inspire the Java development community. My mission is to bridge the gap between theory and practice, making complex programming concepts accessible through well-structured and in-depth educational content.

I regularly publish articles on Java programming, algorithms, and data structures – catering to both beginners and experienced developers.

Additionally, I produce high-quality video tutorials on advanced Java topics, enhancing community learning through engaging visual explanations on the HappyCoders YouTube channel.

Beyond online content, I am an active speaker at Java User Groups (JUGs) and conferences, sharing insights on Java development and best practices with the global developer community. You can find an overview of my previous talks here.

At ICE Services, a leading provider of financial and data services, my role is to optimize Java applications for scalability and performance in a large-scale distributed environment.

• Database Migration & Optimization:
  Led the migration of several terabytes of data from DynamoDB to PostgreSQL, ensuring data integrity and achieving query speedups of up to 1,000x.
• Bulk Update Mechanisms:
  Developed highly efficient bulk update functionalities, enabling seamless modifications across thousands of entity aggregates.
• Asynchronous Processing:
  Transitioned synchronous and asynchronous code to a purely asynchronous model using Mutiny, improving responsiveness and efficiency.
• UI Performance Optimization:
  Designed and implemented a cache layer leveraging Java 21 and virtual threads to enhance UI responsiveness.
• Dependency Consolidation:
  Streamlined dependencies across nearly 100 Java repositories, reducing maintenance overhead and enhancing maintainability.

At IONOS, I optimized Java EE backends and REST APIs within the company's IaaS infrastructure. My work focused on improving system performance, driving architectural modernization, and coaching development teams to tackle complex scalability challenges.

• Achieved a 50x performance improvement under load.
• Led the migration to a modern microservices architecture using Quarkus, ensuring long-term maintainability.
• Designed the next generation IONOS Cloud API for enhanced developer accessibility.
• Implemented zero-downtime deployments for monolithic legacy components.
• Coached developers on modern Java features and best practices in scalability and performance optimization

At NextPit (formerly AndroidPIT), I modernized their digital platform and optimized backend operations.

• Website Migration: Led the transition from androidpit.com to nextpit.com, ensuring a seamless user experience.
• SEO & API Optimization: Adapted the Java-based content management system (CMS) to align with evolving SEO requirements.
• Feature Development: Implemented new functionalities to improve user engagement and platform usability.
• CI/CD Automation: Migrated build automation from Jenkins to GitHub Actions, streamlining deployment workflows.

Fonpit AG, the predecessor of NextPit GmbH, operated AndroidPIT, the world’s largest multilingual Android community. I was responsible for defining and executing the company's technology strategy, ensuring scalability, security, and innovation in a rapidly evolving market.

Technology Leadership & Team Building

• Established and led an agile IT team of up to 15 engineers.

Scalable Infrastructure & Product Innovation

• Designed and built a highly scalable content management system (CMS) to accommodate a growing global user base.
• Transitioned the company's tech stack to modern technologies, including Java 11, Spring 5.1, and Spring Boot 2.1 by 2019.
• Led the GDPR compliance initiative in 2018, ensuring the entire IT infrastructure adhered to EU data protection regulations.
• Developed an advertising infrastructure based on a microservices architecture, leveraging Spring Boot, Spring Cloud, Netflix OSS, and Kubernetes.

Android App Ecosystem & Market Disruption

• Developed the AndroidPIT App Center, a Google-independent app store featuring multiple payment options, developer discounts, and exclusive promotions – pre-installed on devices from various manufacturers.
• Pioneered the first web directory for Android apps in 2009 to enable web-based app discovery – long before Google Play Store had a web presence.

As the Founder and CTO of eleisure AG, a holding company specializing in online gaming, I led the development of multiple innovative projects at the intersection of gaming and technology.

• Developed GameAbo, a game rental platform with integrated logistics and payment systems.
• Created the browser-based MMOG Feenix – The Age of Pirates, awarded “Browser Game of the Year 2005.”
• Built Bailamo, a browser-based 3D community platform.

At 1&1 Internet AG, a leading German Internet service provider that aquired W+R Software GmbH, I led the Windows client development team.

• Built and led a dedicated Windows development team.
• Drove the continued development of the GMX SMS Manager, refining its features for better user experience.
• Redesigned and re-implemented the SMS backbone for the United Internet Group, improving performance and reliability.

Founded W+R Software GmbH, focusing on innovative online messaging services and leading its acquisition by 1&1 Internet AG.

• Developed Germany’s first paid online messaging service, GMX SMS Manager.
• Led the full software development lifecycle, from concept to deployment.
• Managed the company’s acquisition by 1&1 Internet AG in 2002.

At jfax.de GmbH, a local branch of J2 Communications specializing in unified messaging platforms, I was responsible for building the German portal jfax.de. My responsibilities spanned software development, technical leadership, and ensuring a smooth transition of operations to the parent company.

• Led the development of core functionalities of the messaging platform while aligning with business and customer needs.
• Integrated enterprise messaging services.
• Managed the handover of operations to J2 Global in 2000, ensuring a seamless transition of business and technical processes.

Led the technological vision for Cleverlearn, Inc., an innovative provider of online language learning solutions.

• Developed Clicktionary, an interactive Windows-based language learning tool using Visual C++.
• Designed scalable backend infrastructure using Java, JRun, and Oracle DB.
• Led cross-functional software development teams.

During my tenure as a graduate student at amazon.com, I contributed to research and development in data-driven decision-making.

• Designed and developed a software that analyzed historical purchase behavior to generate personalized product recommendations.
• Conducted in-depth data analysis to identify purchasing patterns and trends.