About Gapstars
At Gapstars, we partner with some of Europe’s most ambitious tech companies, from disruptive startups to fast-scaling scaleups, helping them build high-performing remote engineering teams. Headquartered in the Netherlands, with talent hubs in Sri Lanka and Portugal, we are home to 275+ engineers who thrive on solving real-world challenges with modern technologies. Our teams work across domains, from networking and marketplaces to SaaS and AI, delivering scalable solutions that drive meaningful outcomes. If you’re looking for a company that combines technical excellence, a strong culture, and room to grow, welcome to Gapstars.
About the Role
Client is looking for a hands-on Senior Java Developer (ATL/TL level) to take ownership of a complex, legacy Java application landscape running across ~20 servers. The environment uses an older version of GlassFish and has limited documentation. The main challenge is to understand, document, and maintain application-level integrations (how services connect and interact), stabilize the platform, and prepare the ground for future modernization/migrations.
This is not an operations-first system role; it is a development + integration ownership role with strong emphasis on technical discovery, documentation, and legacy platform stewardship.
Key Responsibilities
Take ownership of a legacy Java platform from an application + integration perspective.
Discover, map, and document:
application dependencies, integration points, data flows, interfaces, deployment topology (as relevant), and key runtime/config assumptions
Analyze and resolve complex production issues related to:
Java application behavior, performance bottlenecks, runtime issues, integration failures, and stability concerns
Work with (and gradually build confidence in) the legacy runtime environment, including GlassFish configuration and deployments.
Improve maintainability through:
clear technical documentation, diagrams, runbooks (where useful), better logging/observability recommendations, and incremental refactoring when appropriate
Support and guide engineering standards as an ATL/TL profile:
code reviews, mentoring, technical guidance on integration design and legacy-safe improvements
Collaborate closely with stakeholders to create a shared understanding of “how the platform works” and support migration readiness.
Required Experience & Skills (Must-have)
8–10+ years of strong Java development experience (senior level; legacy experience is a big advantage).
Proven experience working with complex integration landscapes (multiple services/apps, interdependencies, unclear documentation).
Strong debugging and root cause analysis skills: logs, runtime behavior, performance investigation.
Ability to work effectively in ambiguous/legacy contexts and turn it into structured documentation and reliable delivery.
Solid communication skills: ability to explain complex systems clearly to technical and non-technical stakeholders.
Important (Strong preference)
Experience with application servers/enterprise Java runtime concepts (deployments, configuration, resources, runtime tuning).
GlassFish experience is highly valued (but not mandatory if the candidate can ramp up fast).
Experience with cloud environments (either AWS or Azure).
Nice-to-have
Experience with modernization readiness work: documenting legacy platforms for migration, incremental refactoring, improving observability, and reducing coupling.
Prior experience in a lead/ATL/TL capacity: mentoring, owning technical direction for a domain, guiding best practices.
