Built a robust core booking module to handle complex, multi-step flight reservation workflows. The service ensures strict data integrity across multiple relational database tables using transactional boundaries. Key responsibilities Atomic transactions: Applied @Transactional to guarantee that parent booking records (BookingMaster), child entity details (BookingFlight), and payment states succeed or fail as a single unit, preventing orphaned data. Data validation: Implemented rigorous pre-checks for crucial business inputs (flight numbers, PNR codes, routing, and pricing) before any database operations occur. Clean code: Leveraged the Builder design pattern for clean, readable entity construction and maintained strict relational mapping between core operational tables. Tech Stack: Java, Spring Boot, JPA/Hibernate, Relational Database.