Sajjad Khan

Senior Java Backend Engineer

Zone Delivery Service • Tiempo completo

Mar 2021 - Present • 5 yrs 2 mos

As a Senior Java Backend Engineer at Zone Delivery Service, I have been responsible for designing, developing, and maintaining scalable, secure, and high-performance backend systems that power the core delivery operations platform from the ground up. My key contributions and responsibilities over 5 years include: Architected and developed production-grade RESTful APIs using Java and Spring Boot, enabling seamless and secure communication between mobile apps, web clients, and internal backend services. Designed and implemented microservices-based architecture, improving system modularity, independent deployability, fault isolation, and overall application reliability under high traffic conditions. Designed and optimized complex MySQL and PostgreSQL database schemas, writing efficient queries and reducing execution time by up to 70% through proper indexing strategies, query tuning, and connection pool optimization. Built asynchronous order and delivery processing pipelines using RabbitMQ with producer/consumer patterns, dead-letter queues, and retry mechanisms, ensuring reliable and fault-tolerant service communication. Integrated multiple third-party APIs including payment gateways, SMS and push notification providers, and real-time logistics tracking services into the core platform. Implemented robust security using Spring Security, JWT-based authentication, and OAuth2 authorization for fully protected API access across all services. Mentored junior developers, led code reviews, enforced clean code standards, and ensured all deliverables followed SOLID principles and industry best practices. Collaborated closely with frontend teams, mobile developers, and product managers to deliver features on schedule with clear and detailed API documentation using Swagger and OpenAPI.