Modernizing Legacy Systems with Spring Boot Microservices: A Unified Framework for Capital Markets, Travel Logistics, and Financial Services

Abstract

Legacy enterprise platforms in capital markets, travel logistics, and financial services often combine valuable domain logic with tightly coupled deployment, aging integration protocols, and constrained release practices. This article proposes a unified, incremental modernization framework using Spring Boot microservices, domain-driven design, API facades, event-driven integration, automated delivery, and production observability. The framework separates business capabilities while preserving transaction controls, auditability, and compatibility with existing systems. It combines six stages: discovery, domain decomposition, façade-based coexistence, data and event migration, progressive release, and operational optimization. A quantitative assessment model is defined through 15 equations covering service cohesion, coupling, migration priority, risk, latency, availability, recovery, cost, and weighted quality. Two architecture/method figures and five multicolour charts illustrate how the framework can be evaluated. The charts use explicitly hypothetical values rather than measurements from a deployed organization: in the illustrative scenario, p95 latency declines from 420 ms to 245 ms, deployment lead time from 72 to 6 hours, and recovery time from 95 to 22 minutes; change-failure rate decreases from 18% to 8%, while critical-path test coverage rises from 52% to 86%. These values demonstrate a measurement template, not a claim of empirical validation. The contribution is a domain-neutral but control-aware blueprint for staged modernization, with measurable gates for business continuity, security, and service quality. Adoption should be driven by validated baselines, bounded contexts, reversible releases, and evidence-based decisions rather than by microservice count alone.