Sven Woltmann

(Dipl.-Inf.)
Java Scalability and Performance Specialist
Freelancer – Coach – Author of HappyCoders.eu
I’ll help your teams design and implement highly scalable,
stable, reliable, and maintainable Java backend solutions.

Profile

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.

This Is What I Can Do For You

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.

Main Areas of Expertise

Advanced Java

  • New language features (currently Java 16: Pattern Matching for instanceof, Records)
  • Streams, Lambdas
  • Collections Framework incl. queues, deques, concurrent collections
  • Advanced topics: Concurrency, Performance, Reflection, Java Memory Model, Garbage Collection

Microservices and Enterprise Applications

  • 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

Code Quality

  • Clean Code (SOLID principle)
  • Design Patterns
  • Test-driven development (JUnit, TestNG, Hamcrest, Mockito, RestAssured, WireMock, Testcontainers)
  • Static code analysis with PMD, FindBugs / SpotBugs, Checkstyle, SonarQube / SonarCloud / SonarLint, sshgit, Trivy

Let’s Get in Touch!

Have I caught your interest? Then I would like to learn more about your business and challenges. I look forward to hearing from you and a personal dialog to discuss how I can support you.

My daily rate is 1,200 € (plus VAT where applicable).

Contact me at [email protected].

Work

August 2019 – Today
Freelancer

1&1 IONOS
  • 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 2.0, Java 16, 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.
Technologies:
Java EE, Glassfish, Payara, MicroProfile, Quarkus, JPA, Hibernate, EclipseLink, PostgreSQL, Redis, Infinispan, JWT RBAC Security (MP-JWT), Docker, Kubernetes, Kustomize, Helm, Traefik
Performance Improvements
August 2019 – Today
Freelancer

NextPit GmbH
(formerly AndroidPIT)
  • 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.
Technologies:
Java 11, Spring Boot, Spring Cloud, RxJava, JPA, Hibernate, MySQL, Elasticsearch, Filebeat, Kibana, Tomcat, Kubernetes, Docker
NextPit Webseite
2009 – 2019
Founder & CTO

Fonpit AG

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.
Technologies:
Java 11, Spring Boot, Spring Cloud, RxJava, JPA, Hibernate, MySQL, Elasticsearch, Filebeat, Kibana, Tomcat, HAProxy, Kubernetes, Docker, GlusterFS, Ansible
Fonpit-Webseite
Fonpit Webseite
AndroidPIT website
AndroidPIT Website
AndroidPIT App Center
AndroidPIT App Center
2004 – 2009
Founder & CTO

eleisure AG

A holding company for online gaming.
  • 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”.
Technologies:
Java, Spring Framework, Hibernate, Tomcat, MySQL
2002 – 2004
Team Leader Windows Client Development

1&1 Internet AG

In 2002, 1&1 acquired W+R Software GmbH, a software development company founded by my business partner and me.
  • 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.
Technologies:
Java, JMS, JBoss (jetzt WildFly), Borland C++ Builder
Two girls with game console controllers
GameAbo Webseite
Screenshot of the game "Feenix - The Age Of Pirates"
Feenix – The Age Of Pirates
Screenshot of the 3D online community "Bailamo"
3D Community “Bailamo”
2000 – 2002
Founder & CTO

W+R Software GmbH

  • Developed the Windows application "GMX SMS Manager", the
    first paid online messaging service in Germany.
  • Acquired by 1&1 Internet AG in October 2002.
Technologies:
Java, JDO, Tomcat, Oracle DB, Borland C++ Builder
GMX SMS Manager
GMX SMS Manager
1999 – 2000
Lead Software Developer

jfax.de GmbH

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.
Technologies:
Java, JSP, JRun, Oracle DB
jfax.de website
jfax.de Homepage
1999
Founder & CTO

Cleverlearn Inc.

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

  • Development of the Windows application “Clicktionary”
  • Development of the backend software
Technologies:
Java, JRun, Oracle DB, Visual C++
Cleverlearn Clicktionary
Cleverlearn Clicktionary

Education

1994 – 1999
Technical University of Ilmenau

Diplom-Informatiker (corresponds to a Master of Science)

Studied Computer Science with a focus on practical computer science, algorithms and data structures, and database systems.

Graduated with distinction after nine semesters.

1997 – 1999
Amazon.com

Intern and Graduate Student

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

I’m Passionate About

… complex problem solving with attention to detail.

… surprising other developers with new approaches to solutions, inspiring and enabling them to create elegant, intuitive, efficient, and maintainable code themselves.

… the continuous expansion of my boundaries, knowledge, and skills – also in other areas of life like entrepreneurship, marketing, productivity, health, and personality development.

Let’s Get in Touch!

Have I caught your interest? Then I would like to learn more about your business and challenges. I look forward to hearing from you and a personal dialog to discuss how I can support you.

My daily rate is 1,200 € (plus VAT where applicable).

Contact me at [email protected].