When looking for the best vendor for Java banking software development evaluate fintech domain knowledge first, Java seniority second. Ask for specific examples of PCI DSS v4.0 compliance work, open banking API implementations, and payment scheme integrations. Assess their DevSecOps maturity: CI/CD pipelines, security scanning, container hardening, and incident response documentation. Start with a discovery or technical audit engagement before committing to full development. This reveals both their technical capability and their working style.