Željko Kozina
Technical Architect, Api Designer, Security Enthusiast
Dublin, Ireland
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Željko has spent over 15 years in IT, mostly consulting for banks and insurance companies, with a focus on modernising legacy systems. Along the way, he developed deep expertise in JVM-based technologies and has become a go-to voice on topics such as API design. When he's not untangling someone else's technical debt, he's happily creating his own through a growing collection of personal projects he enthusiastically starts and occasionally finishes. Željko is passionate about sharing knowledge in a way that actually sticks, which usually means keeping things practical, a little entertaining, and free of unnecessary jargon.
He is a GraphQL Ambassador and a member of the GraphQL AI Working Group
Area of Expertise
Topics
JSON: The Lingua Franca of APIs (and Everything Else)
Every time you fire an API query, your beautifully crafted response comes back wrapped in JSON. But how well do you actually *know* JSON? Not "I can read it" know, I am talking about "I know exactly where the spec draws the line" know. Buckle up. We're going deep on the most successful data format the web has ever seen.
From Zero to Query: Build, Secure, and Deploy a Production-Ready GraphQL API in One Afternoon
In this hands-on workshop, you'll go from an empty project to a deployed, production-grade GraphQL API, no prior GraphQL experience required. Basic Spring Boot knowledge is desired. Starting with schema design fundamentals, we'll incrementally build a fully functional API using Spring for GraphQL (or your preferred JVM framework). Each module builds on the last: defining your schema and first resolvers, modelling relationships and solving the N+1 problem with DataLoaders, adding field-level authentication and input validation, writing integration tests with GraphQL-specific assertions, and deploying to a live environment. By the end, you'll have a running service you built yourself, a clear understanding of GraphQL's core concepts, and, just as importantly, the judgment to know when GraphQL is the right choice and when it isn't. Bring your laptop and your curiosity.
GraphQL in the Age of Agents: Why Your Next AI Client Speaks in Queries
LLM-powered agents require structured, discoverable, self-documenting APIs, and GraphQL fits perfectly with its introspectable schema and precise data fetching. This talk explores the emerging intersection of GraphQL and AI agents. We'll cover why GraphQL's type system gives agents a major advantage over REST for tool use, how to expose a GraphQL schema as an LLM tool with automatic argument construction from the schema, practical patterns for letting agents compose queries dynamically while keeping cost and complexity bounded, and real-world examples using function calling with OpenAI, Anthropic, and open-source models. We'll build a working agent live that discovers, queries, and mutates a GraphQL API, and discuss guardrails like query allow-lists, mutation scoping, and human-in-the-loop approval for destructive operations.
Trash Talk - Optimising Java Garbage Collection
Understanding how Java organizes memory is important for every Java professional, but this particular topic is a common knowledge gap for many software professionals. This talk will help you understand the different parts of Java memory and the various garbage collectors so you can select your preferred one.
Lets explore how memory management can help you effectively improve performance.
Netflix dropped REST, but should you? REST developers' Assessment of Spring GraphQL
GraphQL is undoubtedly one of the popular kids on the Development playground right now. Last year, Netflix announced that it was dropping REST completely in favour of GraphQL. GraphQL is a new way to build APIs, one that's easier, faster, better, and more flexible than the old RESTful API system, or at least that's the promise. In this session, we will cover the basics of Spring GraphQL, explore its strengths and weaknesses, and determine whether it is a better option for your company than a conventional REST API.
No Country For Old APIs. Wrapping legacy Java services as MCP tools without rewriting them.
Somewhere in your estate is a Java service old enough to vote. REST endpoints by the dozen, one SOAP relic nobody will admit to, session auth, and the person who understood it all has retired. It works, which is why nobody touches it. And now the business wants AI agents to use it.
Every enterprise is under pressure to connect AI agents to systems that were never designed for them, yet most MCP material assumes a greenfield project or a toy demo. This session addresses the situation attendees actually face: a brownfield estate of REST and SOAP services that cannot be rewritten. It is demo-driven, built on the official MCP Java SDK, Spring AI, and Spring for GraphQL, and it is honest about the failure modes: tool sprawl from auto-generation, auth translation, oversized responses, and unsafe retries against non-idempotent writes.
Attendees leave with a reusable pattern set (facade first, curation over generation, read-only first, approval gates) they can apply to their own estate the following week.
The Federation Strikes Back: GraphQL Beyond a Single Schema
Most engineering organisations decomposed their backends into microservices years ago. The client-facing API rarely kept pace: frontends still orchestrate calls across a dozen services, or lean on a gateway that has quietly become a monolith of its own. GraphQL has become a popular answer: a single, strongly typed schema through which clients request exactly the data they need, regardless of which service provides it.
That model carries a quiet assumption, however: one schema, and in practice one team that owns it.
Federated GraphQL removes the assumption. This session introduces federation from the ground up: dividing a graph into subgraphs aligned to existing service and team boundaries, then composing them into a supergraph that clients continue to see as one coherent schema. We will cover the mechanics in plain terms: entities and the @key directive, reference resolvers, how a router plans a single query across several services, and what composition validates at build time versus what still fails at runtime. We will also look at where the ecosystem is heading as the Composite Schemas working group standardises composition beyond any single vendor.
No production GraphQL experience is assumed: familiarity with APIs and microservices is enough.
Porto Tech Hub Conference 2026 Sessionize Event Upcoming
J On The Beach Upcoming
From Zero to Agentic Query in One Afternoon: Build a GraphQL API and Expose It to an LLM Agent via MCP
Dev2Next Upcoming
GraphQL in the Age of Agents: Why Your Next AI Client Speaks in Queries
Devoxx Belgium Upcoming
No Country For Old APIs. Wrapping legacy Java services as MCP tools without rewriting them.
API Days Upcoming
Houston, We Have a Partial Response: GraphQL Error Handling
JConf Dominicana
JConf Dominicana is an annual Java technologies conference organised by the Dominican Republic Java User Group (Aka JavaDominicano). It is created to discuss the latest about the Java ecosystem, including alternative JVM languages, Web, Mobile development, and the most trending Cloud technologies
MakeIT 2026 / JCON OpenBlend Slovenia 2026 Sessionize Event
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