Java / Spring Boot · Web3

Hi, I'm Cem Ayyıldız

Computer Engineering student and software developer. Java 21 / Spring Boot in CrossQuery, plus production Web3: 40K+ users, a published npm package, Sui mainnet, and Stellar invoice tooling.

40K+
Active Users
6+
Projects
1
NPM Package
// Java 21 · Spring Boot · CrossQuery

public record Engineer(
  String name,
  List<String> focus
) {
  static Engineer me = new Engineer(
    "Cem Ayyıldız",
    List.of("Java", "Spring Boot", "REST")
  );
}
Java · Spring
40K+ Users

Professional Journey

Production Web3 at OverBlock, plus Java / Spring Boot in CrossQuery

Software Developer

OverBlock, İzmir | Jul 2025 – Present

Started as an intern, now shipping backend APIs and frontend for blockchain-integrated products, including production deployments.

Software Developer

CrossQuery

Java 21 / Spring Boot

Multi-model ideation panel: research, cross-examine, vote, scored Top-3. JPA, Flyway, validation, background runs, rate limit, SSRF guard, tests and CI.

Java Backend

Web3 Development

Somiverse & mantle-402

Smart contracts, production fixes on a live platform with 40K+ users, PWA for mobile, and an npm package for HTTP 402 payments on Mantle.

Web3

Featured Work

Java backend first, then the production Web3 work

Java / Spring

CrossQuery

Multi-model ideation panel. Models research, cross-examine, vote, and return a scored Top-3. JPA, Flyway, tests and CI.

Java 21 Spring Boot JPA Flyway
Stellar

Quittance

Invoice, pay link or QR on Stellar, Horizon verification (memo, amount, destination), downloadable payment proof.

TypeScript Next.js Stellar
40K+ Users

Somiverse

Smart contracts, production fixes on a live platform with 40K+ users, and a PWA conversion for mobile.

Web3 Smart Contracts PWA React
Mainnet

Mapmark

On-chain location bookmarking on Sui, shipped to mainnet.

Sui Move TypeScript React
npm

mantle-402

HTTP 402 payment flows on Mantle, published as an npm package.

npm Mantle TypeScript
Full-stack

order-system

Real-time restaurant order tracking. TypeScript, Node.js, PostgreSQL.

TypeScript Node.js PostgreSQL

Technical Expertise

Java 21 / Spring Boot, plus the stack I ship in production

Java / backend

Java 21 Spring Boot JPA Flyway REST PostgreSQL SQL

Also ships

TypeScript Node.js React Next.js Express

Blockchain

Stellar Move Solidity Sui EVM

Tools

Git Docker Maven npm

Milestones

Key moments in my professional journey

Jul 2025 – Present

OverBlock: intern to Software Developer

Backend APIs and frontend for blockchain-integrated products, including production deployments.

Current Position
2026

CrossQuery: Java 21 / Spring Boot

Open-source multi-model ideation panel with JPA, Flyway, tests and CI.

Public Repo
2025

Somiverse: 40K+ Active Users

Contributed to a platform with 40,000+ active users. Resolved critical system issues and improved mobile experience by converting the app into a PWA.

40K+ Users
2025

mantle-402: npm package published

Developed a 402 Payment Required-based payment system on Mantle network and published it as an npm package for developer integration.

Published Package
2024 – Present

B.Sc. in Computer Engineering

Currently pursuing Computer Engineering degree at Manisa Celal Bayar University.

2023

Associate Degree in Computer Programming

Graduated from Ege University with a degree in Computer Programming.

Graduate
University

Student Representative, Quality Representative

Served as Student Representative at Manisa Celal Bayar University. Facilitated communication between students and administration, managed feedback processes, and actively participated in organizational and representation duties.

Leadership

Let's Build the Future Together

Focused on Java / Spring Boot, with production Web3 behind me. Open to internships and junior backend roles.

CA