E. Deniz Toktay, Developer in Istanbul, Turkey
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E. Deniz Toktay

Verified Expert  in Engineering

Software Developer

Istanbul, Turkey
Toptal Member Since
February 9, 2022

Deniz is a Java architect, technical team leader, and software developer who has worked on complex projects for multinational companies like Amadeus, Turkcell, Vodafone, Tav Technologies, and others. Having worked in various industries, such as foreign exchange, insurance, travel, and communication, Deniz feels most comfortable solving challenging problems, liaising with multiple teams, mentoring professionals, and solving conflicts in different teams.


Ziiware Inc
Spring Boot, Java, Java 17, Firebase, Cloud Firestore...
Envoy Technology Ltd
Python, Java, Node.js, AWS Lambda, Amazon Web Services (AWS), Architecture...
Kotlin, PostgreSQL, Hasura, GraphQL, JOOQ, MJML, Nylas API, Docker, Jira, Git...




Preferred Environment

Linux, Windows, Eclipse IDE, Android Studio, Visual Studio Code (VS Code), Git

The most amazing...

...thing I've developed is a real-time resource allocation platform, which allocates ground services in Europe's biggest airport.

Work Experience

Spring Boot 3.0 Developer

2023 - 2023
Ziiware Inc
  • Developed security modules to use Firebase tokens for stateless role-based access control (RBAC) for Spring Boot 3.0 and Hilla (Vaadin Confluence).
  • Used JetBrains Space as code repository and tracing tool.
  • Created web security modules for a newly started project to use further developments.
Technologies: Spring Boot, Java, Java 17, Firebase, Cloud Firestore, Role-based Access Control (RBAC), Vaadin, Spring Security, React, JavaScript, TypeScript 3, Frameworks, APIs, REST, REST APIs

Senior Python and Java Developer

2022 - 2022
Envoy Technology Ltd
  • Examined and redesigned the project architecture. Found project defects and security defects. Created reports for the current project and future improvements.
  • Used AWS Lambda to provide a serverless architecture. Used Miro and other tools to provide architectural design and existing defect flows.
  • Redesigned the startup's architecture and roadmap to provide a new pathway to its internal developers, which they had tried to do before but couldn't tackle the development and architectural challenges.
Technologies: Python, Java, Node.js, AWS Lambda, Amazon Web Services (AWS), Architecture, Back-end, Back-end Performance, Back-end Development, APIs

Senior Freelance Developer

2022 - 2022
  • Developed applications to create scheduling between providers and clients.
  • Tracked and fixed bugs using Jira as a reporting tool.
  • Created Datadog dashboards and monitors for the application's health metrics and alarms.
Technologies: Kotlin, PostgreSQL, Hasura, GraphQL, JOOQ, MJML, Nylas API, Docker, Jira, Git, Datadog, Amazon Web Services (AWS), Okta, JUnit, Docker Compose, Spring Boot, SendGrid, Thymeleaf, Testcontainers, Scheduling, Task Scheduling, Amazon Simple Queue Service (SQS), GitHub, Java 11, APIs

Technical Team Lead

2021 - 2022
Vodafone Group
  • Developed and led back-end modules for IoT projects, including registration, billing, and more.
  • Integrated Camunda business process management with the WSO2 authentication system.
  • Defined proof of concept for Camunda business process management's dynamic generation of user tasks.
  • Developed the complex Camunda business process model and notation (BPMN) processes and related actions.
  • Managed a development team and supported other teams as a technical lead.
Technologies: Spring Boot, PostgreSQL, Apache Kafka, MongoDB, Git, Jira, Scrum, Java, Databases, JUnit, Docker, Testcontainers, Docker Compose, SonarQube, Spring, Spring Integration, Spring Batch, WebFlux, Hibernate, Spring Data JPA, Apache Maven, Web Services, SQL, Back-end Development, Back-end Performance, OAuth, OAuth 2, Secure Web Development, Amazon Web Services (AWS), GraphQL, REST, REST APIs, GitHub, Java EE 8, Spring Data MongoDB, Back-end, Back-end Architecture, APIs, Java EE

Freelance Developer

2021 - 2021
Web Help Turkey
  • Converted the existing .NET legacy codes to .NET Core using NuGet.
  • Reviewed and refactored .NET codes to improve Genesys Intelligent Interaction Server communication.
  • Improved the existing development and team development experience. Provided stability to the legacy codebase.
Technologies: .NET, Microsoft SQL Server, Genesys, NuGet, .NET Core, Back-end Development, Back-end Performance

Freelance Developer

2020 - 2021
Web Help Turkey
  • Developed a custom alarm manager to control the scheduled database task completion, emit rest calls to manage scheduled service status, and send notifications via a phone call or email using a custom rule engine.
  • Developed monitoring dashboards and generated reports emailed to managerial users.
  • Completed more than 200 database tasks, emitted more than 50 different service rest calls daily, and generated notifications according to the rules.
Technologies: Java, Microsoft SQL Server, Spring Boot, Windows Server, JUnit, Docker Compose, Docker, SonarQube, Spring Data, Spring Data JPA, Hibernate, Apache Maven, SQL, Back-end Development, Secure Web Development, CI/CD Pipelines, PrimeFaces, REST, REST APIs, Job Schedulers, Scheduling, Java 11

Software Architect Consultant

2020 - 2021
Anadolu Sigorta
  • Developed the architectural design concept for the biggest Turkish insurance company's digital channels using microservices and cloud technologies.
  • Built abstraction and infrastructure libraries to use in microservices.
  • Created third-party connections, such as other internal or external platforms and libraries.
  • Developed common authentication and authorization modules using JSON Web Token technologies.
  • Headed three projects simultaneously to complete their revamp using common architectural principles and standard libraries.
  • Developed the architecture and libraries still used by three mobile and one web project.
Technologies: Java, Oracle, Spring Boot, Jenkins, Spring Cloud, Apache Kafka, Graylog, Hazelcast, Git, Jira, Scrum, DevOps, Databases, Software Architecture, JUnit, Spring, Spring Batch, React Native, React, RxJava 2, Hibernate, WebFlux, Apache Maven, Web Services, SQL, Back-end Development, Back-end Performance, Security, OAuth, OAuth 2, Web Security, Secure Web Development, Java Security, CI/CD Pipelines, Architecture, Microservices Architecture, Domain-driven Design (DDD), Message Queues, REST, REST APIs, Python 3, Java 11, MongoDB, Back-end, Back-end Architecture, Back-end Admin Systems, Mobile Back-end, APIs, Java EE

Senior Software Engineering Consultant

2018 - 2020
TAV IT Services
  • Participated in developing the new Istanbul airport's ground service allocation platform as a technical lead and software architect.
  • Built an abstraction library for microservices, such as security, data source connection, messaging, and more.
  • Developed messaging and other orchestration modules.
  • Integrated platform health tools, such as Grafana and Prometheus, into all developed modules.
  • Used Python to develop custom deployment tools compatible with the Bamboo platform and distributed them to remote restricted Windows servers.
  • Developed integration modules to obtain real-time data from aircraft and ground handling units, such as flight data rosters.
  • Contributed to developing the sorting algorithm to match tasks and resources using predefined rules.
  • Tracked and fixed bugs using Jira as a reporting tool.
  • Activated the platform before the start of the pandemic. It handled more than 1,500 flights per day using real-time data from aircraft.
Technologies: Java, Microsoft SQL Server, Python 3, Git, Spring Boot, Prometheus, RabbitMQ, Jira, Scrum, DevOps, Databases, Software Architecture, JUnit, Apache Kafka, Elastic, SonarQube, Spring, Spring Integration, Spring Batch, Keycloak, REST APIs, Hibernate, Apache Maven, Web Services, SQL, Back-end Development, Back-end Performance, Back-end, Security, OAuth, OAuth 2, Web Security, Secure Web Development, Java Security, CI/CD Pipelines, Microservices Architecture, Spring Microservice, Domain-driven Design (DDD), Message Queues, OpenShift, REST, Scheduling, Job Schedulers, Task Scheduling, GraphQL, Java 11, MongoDB

Senior Software Engineering Consultant

2018 - 2018
  • Developed the payment integration for the BiP messaging platform and end-to-end testing suite.
  • Created proof of concept for the existing BiP platform and their business services.
  • Developed basic image-creating tools to send daily notifications to subscribed users.
Technologies: Oracle, MongoDB, Apache Kafka, Docker, Python 3, Git, Scrum, Java, Spring Boot, Databases, JUnit, Docker Compose, Spring, Spring Batch, Hibernate, RxJava 2, Akka, Apache Tomcat, Gradle, Web Services, SQL, Back-end Development, Back-end Performance, Secure Web Development, Message Queues, Kubernetes, Helm, APIs, REST, REST APIs, SOAP, Java EE 8, Java EE

Master Software Development Engineer

2014 - 2018
  • Participated in developing and headed the airline loyalty platforms, client contact center platform, mail parsing and assignment platform, and reporting tools as a technical lead.
  • Tracked and fixed bugs using Jira as a reporting tool. Became the first point of contact for clients with security issues as a white hat developer.
  • Prepared and conducted secure development lifecycle and defensive programming training sessions within the company, which significantly reduced security-oriented bugs.
  • Released the new platforms enabling Amadeus to sell them to major airlines in the Middle East, Eastern European, and Central American regions.
Technologies: Secure Web Development, JSF, Jakarta Server Pages (JSP), Oracle, PrimeFaces, Git, Scrum, Java, Spring Boot, Databases, Oracle PL/SQL, SonarQube, JUnit, Spring, Spring Integration, Spring Batch, EclipseLink, Hibernate, Apache Tomcat, JBoss AS, WebSphere, Apache Maven, Web Services, SQL, Back-end Development, Back-end Performance, Security, Back-end, OAuth, OAuth 2, Web Security, Java Security, REST, PL/SQL, SQL Stored Procedures, APIs, REST APIs, SOAP, Java EE

Senior Software Engineering Consultant

2012 - 2013
Destek Menkul Değerler
  • Developed real-time news feed, recommendation, and price servers for FX users.
  • Created a web push comet server for HTML4 standard using Python and Twisted framework.
  • Developed JavaScript to get web push records in HTML4 web pages.
Technologies: Python 2, Twisted, MySQL, PyQt 4, JavaScript, REST APIs, Apache HTTP Server, Web Services Description Language (WSDL), Web Services, SQL, Back-end Development, REST

New Generation Insurance App Juno

Juno is a mobile application that allows users to buy different types of insurance. I worked on it as a technical architect and back-end engineer. The application was awarded a silver prize in the Turkish Customer Experience Awards.

Asenta Agent Portal | Mobile App

I worked as a technical architect and back-end developer on the revamp project of the Asenta agent portal and insurance API platform. More than 3,000 agents use the Asenta platform daily to handle all insurance operations. It uses the same back-end servers as the Ofisim Cepte mobile app. A custom rule-based authorization service has been implemented to cover flexible authorization changes based on user type, platform, IP definitions, etc.

Sigortam Cepte Insurance | Mobile Application

The Sigortam Cepte mobile application enables Anadolu Sigorta's clients to handle all their insurance-related operations, such as renewing and claiming premiums, reporting damage, buying health insurance, and more. I worked as a technical architect and technical lead on this application.

Ground Handling Suite

I contributed to the project's architecture and development phases by creating proof of concept and drafting architectural designs. Also, I developed a project skeleton and abstraction tools for the microservices, third-party integration, and a real-time data consumption and orchestration module. A custom Python-based distributed deployment module for Windows servers was developed.

Elemy Main Suite

Elemy is a VC-funded startup that provides home care for children who have autism. The main functionality is to match children with a suitable child psychologist and create their appointments automatically.

I participated in the design and development of matching and scheduling back-end modules. New modules and several integrations, such as AWS, Nylas, Twilo, and so on, were developed using Kotlin and Spring Boot.
2005 - 2010

Bachelor's Degree in Computer Science

Macquarie University - Sydney, Australia


AI for Trading



Deep Learning



REST APIs, Java Security, React, RxJava 2, JOOQ, Nylas API, PyQt 4, Node.js, Natural Language Toolkit (NLTK)


RabbitMQ, Docker Compose, Apache Maven, Git, Jenkins, SonarQube, Apache Tomcat, Jira, SendGrid, GitHub, NuGet, Graylog, OneSignal, Grafana, Elastic, Keycloak, Apache HTTP Server, Gradle, Helm, Amazon Simple Queue Service (SQS)


Spring Boot, JSON Web Tokens (JWT), JUnit, Spring, Spring Batch, Hibernate, OAuth 2, PrimeFaces, Jakarta Server Pages (JSP), Spring Microservice, Flutter, Spring Integration, WebFlux, JSF, .NET, .NET Core, React Native, Akka, Twisted, MJML, Thymeleaf, Vaadin, Spring Security


Java, Python, Web Services Description Language (WSDL), SQL, Kotlin, Python 3, Python 2, JavaScript, GraphQL, Dart, Java 11, Java EE 8, Scala, TypeScript 3


Microservices Architecture, REST, Back-end Architecture, Scrum, DevOps, Role-based Access Control (RBAC)


Oracle, Docker, Apache Kafka, Amazon Web Services (AWS), Windows Server, WebSphere, Kubernetes, OpenShift, AWS Lambda, JVM, Blockchain, Firebase, Java EE


Oracle PL/SQL, Spring Data JPA, Spring Data, MySQL, PL/SQL, SQL Stored Procedures, Databases, Hazelcast, PostgreSQL, Hasura, Microsoft SQL Server, Couchbase, Spring Data Elasticsearch, JBoss AS, Datadog, Spring Data MongoDB, MongoDB, Cloud Firestore


Software Architecture, Distributed Systems, Spring Cloud, LDAP, Testcontainers, EclipseLink, Web Services, Back-end Development, Back-end Performance, OAuth, Secure Web Development, Web Security, Architecture, Domain-driven Design (DDD), Message Queues, Scheduling, Back-end, Back-end Admin Systems, Mobile Back-end, Security, Prometheus, CI/CD Pipelines, Deep Learning, Genesys, AS400, Okta, Job Schedulers, Task Scheduling, Java 17, Frameworks, APIs, SOAP, Natural Language Processing (NLP), Trading, Stock Market, Stock Exchange, Stock Price Analysis, Bonds, Fintech

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