Leonid K.

Is your Java backend difficult to maintain, slow to change, or struggling with complex integrations? I help teams stabilize, extend, and modernize existing applications—without losing sight of production reliability. I'm a senior Java backend engineer working in software development since 2017. My experience includes enterprise applications, complex business rules, REST APIs, database persistence, automated testing, and legacy codebases. I've also held Team Lead responsibilities, including architectural work, managing a 10-person team, and interviewing Java developer candidates. What I can help with: • Troubleshooting difficult backend bugs, Hibernate/JPA issues, and performance problems • Building and improving REST APIs and third-party integrations • Maintaining and modernizing Spring, Struts, JSP, and other Java applications • Reviewing architecture, improving code quality, and adding automated tests • Supporting backend features from investigation through delivery Core technologies: Java, Spring Framework / Spring Boot, Spring Security, Spring Data, Hibernate/JPA, JDBC, SQL, PostgreSQL, MySQL, REST APIs, Struts, JSP, and automated testing. I also have WebRTC/VoIP and cloud-environment experience. My previous Upwork clients gave me five-star reviews, highlighting Java expertise, architectural thinking, testing practices, self-management, and teamwork. If you need an engineer who can understand an existing system, communicate trade-offs clearly, and take ownership of a backend problem, let's discuss the scope and a practical way forward.