Hello,

Welcome to Development Site

Freelance Java developer

DEVSITE is Constantin Lungu - a freelance senior Java developer. I design and build scalable Spring Boot backends, microservices and distributed systems, from SEPA payment rails at Revolut to aviation data platforms at EUROCONTROL. Available remotely, worldwide.

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Our stack

Java
Kotlin
Spring
Dart
Flutter
React
Next.js
TypeScript
PostgreSQL
MySQL
MongoDB
Kafka
Google Cloud
Azure
Docker
Kubernetes
Git
Gradle
Maven
TeamCity
Vercel
Grafana
Kibana
New Relic
IntelliJ IDEA
Jira
Confluence
Claude

Java
Kotlin
Spring
Dart
Flutter
React
Next.js
TypeScript
PostgreSQL
MySQL
MongoDB
Kafka
Google Cloud
Azure
Docker
Kubernetes
Git
Gradle
Maven
TeamCity
Vercel
Grafana
Kibana
New Relic
IntelliJ IDEA
Jira
Confluence
Claude

Services

How I can help

One senior engineer, end to end - from architecture and backend to the web front ends that bring it all together. No hand-offs, no middlemen.

Custom Backend Development

Need a senior engineer to turn your idea into a production backend? I design and build bespoke Spring Boot services and microservices from scratch - clean, well-tested code you can keep building on.

springjavagit

API Development & Integration

I build robust REST and GraphQL APIs and connect your systems to third-party and payment providers - including event-driven integrations with Kafka, up to regulated, high-throughput production traffic.

rest-apikafkateamcity

Refactoring & Modernisation

Slow, brittle or ageing backend? I rebuild it in place, leaving your front end intact - upgrading to current Java and Spring, cutting technical debt and making the codebase safe to change again.

integration-testunit-test

Mobile App Backend

I build fault-tolerant back ends for native and cross-platform apps - plus the Flutter/Dart client when you need it - with secure auth, clean APIs and reliable data sync across devices.

dartfluttergradlejava

Web Applications

I design and ship fast, high-performance sites and portals with Next.js and TypeScript, backed by a solid Spring or serverless backend - from marketing sites to data-heavy web apps.

next.jstypescriptspringmaven

Cloud & DevOps

I containerise your services, automate delivery pipelines and run resilient workloads on Azure and Google Cloud - with monitoring, logging and alerts wired in so you know it stays healthy.

dockerkubernetesazuregcp

Timeline