Java Developer · Backend Engineer

Building robust
systems with Java.

Backend development specialist with Java, Spring Framework, REST APIs and scalable architectures. Focused on clean code, performance and long-lasting solutions.

View projects Get in touch
// overview
Experience +9 yrs
Projects delivered +12
Companies served 3
APIs built +30
// core stack
Java 17+ Spring Boot REST SOAP PostgreSQL Docker
// 00 — ABOUT

Java backend developer with over 9 years of experience (2009–2019), specialised in the Spring ecosystem and the development of high-complexity systems for government and enterprise sectors.

My journey includes contributions to real-impact projects — from electronic tax systems for the Government of the State of Goiás (PAT-e), to an R&D project funded by a non-reimbursable federal grant from FINEP/Tecnova, where I developed SOAP integrations with government services and a Multitenancy SaaS login module. I also have a scientific publication accepted at the XV Brazilian Congress on Health Informatics (CBIS 2016).

Technically, I master Java (8–17), Spring Boot, Spring MVC, Spring Security, REST and SOAP APIs, Hibernate/JPA, Oracle and PostgreSQL, with solid CI/CD practices via GitHub Actions, Docker and testing with JUnit and Mockito.

Currently based in Sint-Niklaas, Belgium, I speak Portuguese natively, English (A2) and advanced French (C1), and I am actively reintegrating into the IT market after a period in civil construction.

📍
Location Sint-Niklaas, Belgium
🎓
Education Systems Analysis & Development — SENAI (2015–2017)
🌐
Languages Portuguese (native) · French C1 · English A2
📄
Publication CBIS 2016 — Kyklos Recycling Cooperative Management System
🏆
R&D Grant FINEP / Tecnova 2013 — Federal non-reimbursable subsidy
// 01 — STACK
CORE
Java Platform
Java 8–21 Java EE Jakarta EE Maven Gradle JUnit
FRAMEWORK
Spring Ecosystem
Spring Boot Spring MVC Spring Security Spring Data JPA Spring Cloud
API
Integration & APIs
REST RESTful SOAP / WSDL Swagger OpenAPI JWT / OAuth2
DATA
Database
PostgreSQL MySQL Oracle DB Hibernate Redis MongoDB
// 02 — PROJECTS

Projects developed

Backend solutions built in personal and professional projects — solid architectures, clean code, and APIs that scale.

001 — Featured ● Live

Financial Management System

Full RESTful API for enterprise financial control. JWT authentication, real-time reports, legacy system integration via SOAP and microservices architecture with Spring Cloud.

Java 17 Spring Boot 3 Spring Security PostgreSQL SOAP Docker REST API
View project
@Controller
@RequestMapping("/pat")
public class ProcessoCtrl {
 
  @Autowired
  private ProcessoService svc;
 
  @GetMapping("/contribuinte")
  public String
  painel(Model model) {
    model.addAttribute(
     "processos",
     svc.findAll());
    return "painel";
  }
}
002 ● FINEP / Tecnova Grant

Intelligent Social Network for Tax Management

R&D project awarded a non-reimbursable federal grant (FINEP/Tecnova 2013). Developed SOAP integrations with government services, Multitenancy SaaS login module, technical specifications and new module development. @ Ambient Informática.

Java SOAP / WSDL Web Services Multitenancy SaaS FINEP Grant
View details →
003 ◐ In development

Centralized Auth API

Centralized authentication and authorization service with OAuth2, OpenID Connect and JWT token management for multiple applications.

Spring Security OAuth2 JWT Redis
View details →
004 ● Live

Personal Portfolio

Full-stack portfolio with Node.js backend, multi-container Docker setup with Traefik reverse proxy, automated SSL, CI/CD via GitHub Actions and transactional email via Resend.

Node.js Docker Nginx Traefik Resend GitHub Actions
View details → + Case study
✅ Positives
  • Complete end-to-end ownership — from design to production deployment
  • CI/CD pipeline fully automated via GitHub Actions on every push
  • Multi-container architecture with clean separation of concerns
  • SSL certificate managed automatically by Traefik + Let's Encrypt
  • Transactional email with verified domain via Resend
  • Multi-language support (EN, PT-BR, FR-BE, NL-BE)
❌ Challenges
  • Traefik routing with multiple Docker networks caused hours of debugging
  • Git conflicts between local VPS edits and GitHub Actions deploy workflow
  • Resend DNS propagation required patience to verify records
  • Separating HTML/CSS/JS required Dockerfile updates not initially committed
🔧 Technical difficulties
  • Traefik v3 picks the wrong network IP when container has multiple networks — fixed with traefik.docker.network label
  • Nginx SPA fallback masked missing JS/CSS files — showed as syntax error in browser console
  • Docker build cache ignored new folders because COPY instructions were missing from Dockerfile
  • GitHub Actions git pull aborted due to local VPS changes — solved with git reset --hard
💡 Learnings
  • Always add traefik.docker.network when a container is on multiple Docker networks
  • Never edit files directly on VPS without committing — always go through Git
  • Traefik debug logs (--log.level=DEBUG) are essential to diagnose proxy issues
  • Resend is far superior to Gmail SMTP for domain-based transactional email
  • Separating HTML/CSS/JS from the start saves refactoring time later
+
Add project
// 03 — EXPERIENCE

Professional journey

Building backend solutions across different industries and contexts.

2017
—
2019

Java Developer

// Engesoftware Tecnologia S.A.

Development of solutions for government systems in the tax area. Analysis, development and maintenance of systems for electronic tax administrative processes. Implementation using Java and corporate frameworks.

2016
—
2017

Systems Analyst Programmer

// B2Br Consultancy

Maintenance and evolution of corporate systems. Systems development, bug fixing and application performance improvement. Technical support and incident analysis.

2015
—
2016

R&D Analyst

// Ambient Informática LTDA

Development of solutions focused on system integration. Gathering functional and non-functional requirements. Implementation of Web Services for communication between platforms. Active participation in the complete development cycle.

2015
—
2015

Software Developer

// Indra Software Labs

Experience with the WEB-LICENÇAS system (Environmental Licensing). Gathering and analyzing user requirements. Developing and implementing functionalities. Ensuring quality and adherence to business rules.

2013
—
2015

Technical Solutions Analyst

// Tax Administrative Council (CAT)

User support, Java development and maintenance of corporate systems. Support for applications developed with Visual Basic Access.

2011
—
2013

Technical Solutions Analyst

// PA Arquivos LTDA

Implementation of GED system and operational training. Responsible for defining software, hardware and technological support processes. Selecting and supervising the technical team for system administration.

2009
—
2011

IT Support

// Agência Goiâna de Esporte e Lazer

Development of operational workflow for athlete registration system. IT solutions for processing and directing registration data. Integration with label printers and badges (Zebra).

+5 yrs
Building Java systems in production environments
+30
APIs designed and documented with Swagger / OpenAPI
3
Legacy system migrations to modern architecture
CBIS 2016
Published research in Health Informatics (CBIS 2016)
SENAI
Associate Degree in Systems Analysis and Development (2015–2017)
// 04 — CONTACT

Let's build something solid together.

Open to opportunities as a senior Java developer, freelance projects and technical consulting. If you need a robust backend, we're on the same page.

LinkedIn linkedin.com/in/gustavo-simoes
→
GitHub github.com/gustavo-as
→
Resume Download PDF
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