Case studies / Java & integrations

Systems that had to keep working.

Selected projects from banking, payments, and healthcare: the problem, what I did, and what changed. Client names are withheld to respect confidentiality.

US banking platform

Built a retail bank client-onboarding platform end to end

Problem
A retail bank needed a responsive client-onboarding flow and staff back office that could support multiple client paths while meeting KYC and regulatory requirements.
Approach
Owned the system from requirements gathering and architecture through release. Built Java and React features, integrated identity-verification, document-management, and Google Maps APIs, automated SFTP and email workflows, and added Cypress suites for every onboarding scenario.
Outcome
Replaced a manual intake process, automated recurring back-office work, and de-risked releases during a major platform overhaul.
  • Java
  • Spring Boot
  • React
  • Material UI
  • Cypress
  • REST APIs

Global payments platform

Moved critical payment flows from a monolith to services

Problem
A global payments product needed to evolve beyond a monolithic PHP application without disrupting payment operations across multiple regions.
Approach
Built React, Node.js, and Spring Boot services while maintaining the legacy PHP and Java systems in parallel. Helped teams find common ground during the migration, created internal libraries to speed up delivery, and added load balancing, health checks, and custom tracing across multi-application workflows.
Outcome
Helped move critical flows onto the new architecture while keeping the existing platform stable, making releases easier to verify, and improving visibility across distributed services.
  • Java
  • Spring Boot
  • Node.js
  • React
  • PHP
  • Sass

Healthcare communications platform

Strengthened reliability across critical clinical workflows

Problem
A doctor-patient messaging platform depended on reliable integrations and well-tested workflows while support issues created daily operational overhead.
Approach
Shipped backend features, integrated Twilio and DrChrono, maintained more than 800 unit and integration tests, and improved resilience with redundancy and circuit-breaker patterns.
Outcome
Improved platform reliability, enabled core clinical functionality, and automated reporting and support workflows that previously consumed staff time.
  • Java
  • Spring
  • Node.js
  • PostgreSQL
  • Kubernetes
  • Twilio
  1. Mar 2023—NowSenior Full Stack EngineerRetail Bank
  2. Jul 2022—Mar 2023Backend EngineerTrueNorth
  3. Jul 2021—Jul 2022Backend EngineerMedici
  4. Jun 2020—Apr 2021Software ConsultantIndependent Freelancer
  5. Mar 2020—Feb 2021Full Stack EngineerdLocal
  6. Jan 2018—Feb 2020Full Stack EngineerBlue Trail Software
  7. May 2016—Jan 2018Full Stack EngineerNetLabs
  8. Aug 2014—May 2016Java Software EngineerGEOCOM

Backend systems

  • Java
  • Spring Boot
  • Spring Data
  • Hibernate
  • Node.js
  • Go

Architecture and integration

  • Microservices
  • Third-party integrations
  • Payment integrations
  • Banking integrations
  • Healthcare integrations

Data and delivery

  • PostgreSQL
  • MySQL
  • Oracle
  • Kubernetes
  • CI/CD

Product interfaces

  • React
  • TypeScript
  • Angular

The best first message tells me what is broken, what you have already tried, and roughly when you need it fixed. I’ll tell you honestly whether I’m the right person — and if I’m not, I’ll usually know who is.

Email: me@gaabmarquez.com