Java 8 → Spring Boot 3
A logistics company was running a 15-year-old Java 8 system: barely maintainable, new features took weeks, and nobody dared to change anything. In 6 weeks the core was modernized – while the system stayed live.
The problem
The monolith had grown over 15 years: Java 8, outdated libraries, no automated test coverage, no CI/CD. Every change to a core module was a risk, releases were manual work, and new features took weeks instead of days. A "big bang" rewrite would not have been acceptable for live operations.
The solution
Instead of rewriting everything, the system was modernized module by module. One core module per week: migration path to Spring Boot 3 and Java 21, tests added, deployment automated. That way the application stayed in production throughout the migration – and the team could sign off each step individually.
Step-by-step approach
- Codebase analysisDependencies, risks and candidates for the core modules identified and prioritized.
- Migration strategyOrder, rollback paths and test coverage defined per module – including a written migration plan.
- Module-by-module migrationOne core module per week onto Spring Boot 3 with Java 21, Hibernate/JPA upgrade and clean REST interfaces.
- Tests & CI/CDUnit and integration tests added, build pipeline automated, deployment standardized.
- Operations & handoverMonitoring, logging and documentation handed over – development and operations started together.
The result
Development time for new features dropped by around 60 %, the code is testable, documented and on a current stack. The team can ship changes again without spending weekends in the office. And most importantly: the migration ran without any downtime in production.
Who this approach is for
- Companies running Java 8/11 applications that still need to work for years
- Teams without test and deployment automation that dread every release
- Live systems where downtime is simply not acceptable
- Budgets where a complete rewrite is not an option
Further references
Two more projects from related fields.
PHP monolith → React/Next.js
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AI-generated code made production-ready
An AI-generated prototype without auth and tests became a stable, secure application in 4 weeks.
Get rid of Java legacy – without downtime?
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I have been developing Java applications for over 10 years – from Java 5 to Java 21. I know the pitfalls of legacy migrations and ensure a smooth transition while the system keeps running.
Stack: Java 8–21, Spring Boot 3, Hibernate/JPA, React • Approach: pragmatic, transparent, production-focused.