Denys

Denys S.
Java Full-Stack Developer

Profile

Full Stack Java Developer with nearly 8 years of experience in building high-volume, mission-critical
applications. Proficient in Java, Spring, Hibernate, and modern frontend (mainly React.js, Vue.js)
frameworks. Experienced with microservices architecture, Kubernetes deployments, and Azure
services as well as AWS (EC2, S3, Load Balancer). Confident in working with Apache Tomcat and
code quality tools like JetBrains Qodana. Strong background across multiple domains: healthcare
(document management, ECM), education, telecom, e-commerce/retail, lottery & gambling, and
information portals. Hands-on experience with legacy enterprise platforms such as Liferay,
comfortable working with Java EE, JSP/Servlets.

Skills

Java, J2EE, JSP/Servlets, Spring (Core, MVC, JavaScript, jQuery, Angular, Vue.js, React.js,
Security, Boot), Hibernate, JPA, REST, Apache Redux, NgRx, TypeScript, HTML, CSS, Webpack,
Tomcat, Gradle, Maven Npm, JSF, PrimeFaces, ICEfaces, AUI JS, YUI JS
SQL, MS SQL Server, Oracle, PostgreSQL, MySQL IntelliJ IDEA, Git (GitHub, GitLab), Jenkins, Jira,
Serenity, Cucumber, Balsamiq, Apache
Liferay (6, DXP), Alfresco, CMIS, Kafka, Subversion
Elasticsearch, Logstash, Kibana, OpenCMS,
Jasper Reports, OWASP ZAP, CKFinder, CKEditor, Linux, Agile, Scrum, JetBrains Qodana, LDAP
Tokbox, Azure, AWS (EC2, S3, Lambda) authentication
Claude Code, Codex, MCP, RAG Docker / Kubernetis

Languages

Ukrainian, russian English
Native Upper-Intermediate

Projects

09/2025 - Present BUSINESS TRAVEL & EXPENSE MANAGEMENT PLATFORM
Description: Enterprise platform for tracking and managing business travel
and employee expenses, including travel- and leave-related costs. The
project was an existing production system with a large legacy codebase. My
role was dedicated to technical modernization rather than feature
development: upgrading the application stack while preserving the original
business behavior, integrations, and production stability.
Responsibilities:
• Upgraded Java from 8 to 25 and migrated the application to Spring Boot 4
• Upgraded Hibernate to 7, JUnit to 5, Mockito to 5, and modernized the
Jackson stack
• Migrated AWS integrations from AWS SDK for Java v1 to AWS SDK for Java
v2

• Upgraded Elasticsearch and Drools to current versions, along with other
core dependencies
• Identified and remediated security vulnerabilities in legacy dependencies
by upgrading affected libraries and resolving compatibility issues
introduced by security fixes
• Adapted deprecated and incompatible APIs, configuration, persistence
code, and tests to the new library versions
• Resolved migration-related regressions and compatibility issues across
modules
• Preserved existing business logic and functional behavior throughout the
modernization process
• Maintained and updated automated tests to validate behavior after the
upgrades
Platform: Java 25
Technologies: Spring Boot 4, Hibernate 7, JUnit 5, Mockito 5, Jackson, AWS
SDK v2, Elasticsearch, Drools

03/2021 - 09/2025 EDUCATION PORTAL
Description: The product is a learning platform used by Canadian
universities, students, and employers. It’s a complex system composed of
multiple loosely coupled modules: each responsible for a specific part of the
platform (e.g., calendar, job board, course management). The architecture
evolved towards microservices to improve scalability and allow
independent deployment of modules. I was actively involved in supporting
and extending key modules on both frontend and backend. Role-based
access control was a core part of the system - depending on whether the
user is an admin, student, employer, or university representative, the
dashboard and available features changed accordingly. Students could
manage profiles, enroll in courses, apply to internships and jobs, and
organize their events in a built-in calendar, similar to Google Calendar.
Employers could publish job openings and internship opportunities.
Some services were containerized using Docker and deployed via
Kubernetes on AWS infrastructure. This setup allowed for scalable
deployment and streamlined CI/CD processes for different environments.
Responsibilities:
• Developed backend and frontend features for key modules
• Participated in architectural evolution towards microservices
• Containerized services using Docker and assisted with Kubernetes
deployments
• Collaborated with DevOps engineers on AWS-based deployment pipelines
• Conducted code reviews and ensured code quality standards
• Refactored legacy code and optimized existing logic
• Troubleshot and fixed production issues under tight deadlines
• Contributed to design discussions and long-term system improvements
• Worked closely with cross-functional teams to deliver scalable solutions
Platform: Java 11, Apache Tomcat
Architecture: Monolith evolving into Microservices
Deployment: Kubernetes, AWS
Databases: MS SQL Server
Technologies: Spring, Spring MVC, Hibernate, Elasticsearch, Apache Log4j,
Apache Subversion, jQuery, Vue.js, React.js
Third Parties: CKFinder, CKEditor, Tokbox
Tools: IntelliJ IDEA, GitHub, Docker

04/2019 - 03/2021 PLATFORM FOR MANAGING LOTTERY ACCOUNTS
Description: The platform is designed to allow managers to process lottery
games, and manage user accounts and their permissions to different
resources. The key features provide:

• lotteries creation and management
• accept users accounts, their payment data, and permissions
management
• envisage users ability to log in using either LDAP username or password
stored in the database, or both
Also migration from WildFly 18 to WildFly 26 was provided.
Responsibilities:
• Creating back-end and front-end
• Optimizing and refactoring of source code
• Implementing new features on back-end and front-end
• Managed deployment with Azure
• Resolve complex technical design issues
Platform: WildFly
Databases: Oracle, PostgreSQL
Technologies: Spring Frameworks, Hibernate, JPA, JSF, PrimeFaces, CDI (Java
EE), Azure, OpenCMS, ES6, HTML, Less
Tools: IntelliJ IDEA, Git, Maven

06/2020 - 03/2021 SELFCARE
Description: User’s account manager where user can manipulate with his
bills, mobile services (recharge sim cards, activate some new options,
review traffic details and so on), shipments.
Responsibilities:
• Creating back-end and front-end
• Optimizing and refactoring of source code
• Implementing new features on back-end and front-end
• Resolve complex technical design issues
Platform: Apache Tomcat
Technologies: Spring Boot, Spring Security, Angular, SOAP, Angular 5,
React, Redux, NgRx, Saga
Tools: IntelliJ IDEA, Git, Maven

01/2019 - 04/2019 TIMETRACKING
Description: This project involved the design and development of a custom
Liferay portlet aimed at streamlining and improving the process of
reporting working hours within an organization using Redmine as the issue
and project tracking system. The portlet serves as a user-friendly web
service that integrates seamlessly with Redmine to help employees
consistently log their working time, ensuring accurate project tracking and
resource management.
Responsibilities:
• Creating back-end and front-end
• Implementing new features on back-end and front-end
Platform: Java
Databases: MySQL
Technologies: Java, OWASP ZAP, Spring MVC, Hibernate, JPA, jQuery,
React.js, Redux
Third parties: Jasper Reports
Tools: IntelliJ IDEA, Git, Jenkins, Balsamiq, Serenity, Cucumber, Jenkins

02/2018 - 01/2019 INFORMATION PORTAL
Description: Informational site with multi-functional tools.
Responsibilities:
• Creating back-end
• Design and update software database
• Optimizing and refactoring of source code
• Implementing new features on back-end

Platform: Liferay 6
Databases: MS SQL
Technologies: Java, JSP, Spring, JavaScript
Tools: IntelliJ IDEA, Subversion

09/2017 - 02/2018 STORE TASK MANAGEMENT PORTAL
Description: The portal is designed to operate a chain of stores and their
franchises. The main task is the ability to create tasks for stores and track
the implementation of tasks.
Responsibilities:
• Creating back-end
• Design and update software database
• Optimizing and refactoring of source code
• Implementing new features on back-end
Platform: Liferay DXP
Databases: MySQL
Technologies: Liferay DXP/Portlets, JSF/ICEfaces, Hibernate, JPA, Java, JSP,
Spring, Solr, JavaScript, AUI JS, YUI JS
Tools: IntelliJ IDEA, Git

05/2016 - 09/2017 CONTACT MANAGEMENT SYSTEM
Description: Documents’ management system where users manipulate with
their documents (upload, download, exchange).
Responsibilities:
• Creating back-end
• Optimizing and refactoring of source code
• Implementing new features on back-end
• Resolve software errors accurately on time and provide required status
reports
Platform: Apache Tomcat
Technologies: Spring Boot, Spring Security, Angular 7
Tools: IntelliJ IDEA 18.x, Git, Gradle

Education

2012 - 2018 Master’s degree
Kharkiv, Ukraine Kharkiv National University of Radio Electronics