Java developer Jobs in Green Bay, WI

Mercor is partnering with a **frontier AI research lab** to engage experienced software engineers with deep expertise in **legacy codebase migration and modernisation**. We are looking for engineers who have personally executed complex migrations across **large, production-grade systems**, particularly in **financial services, fintech/payments, insurance, healthcare, telecom, large technology companies, and other mission-critical enterprises**. Strong hands-on experience with production migrations is the primary qualification. ## What You'll Do - Design, implement, review, and evaluate complex **codebase migration and modernisation tasks**. - Analyse legacy code, dependencies, APIs, databases, build systems, and infrastructure to determine safe migration approaches. - Preserve **functionality, backwards compatibility, data integrity, security, and performance** during migrations. - Develop tests and validation strategies to identify migration regressions and behavioural differences. - Evaluate AI-generated migration solutions for **correctness, completeness, maintainability, and production readiness**. ## Relevant Migration Experience Candidates should have deep expertise in **one or more** of the following: - **Language/version:** Java 8 → 17/21, legacy .NET → modern .NET, Python 2 → 3, PHP 7 → 8 - **Language rewrites:** COBOL → Java/Python, JavaScript → TypeScript - **Frameworks:** Angular, Rails, Django, Spring/Spring Boot, , Next.js/Astro, and other major framework upgrades/replacements - **Databases & ORMs:** Oracle/MySQL → PostgreSQL, SQL → NoSQL, Hibernate → jOOQ, Sequelize → Prisma, raw SQL → ORM - **Infrastructure:** VMs/bare metal → containers, Docker/Kubernetes, cloud-native architectures - **CI/CD:** Jenkins/Travis → GitHub Actions, GitLab CI, or modern deployment pipelines - **Build/package tooling:** Maven → Gradle, Webpack → Vite, CRA → Next.js, npm → pnpm - **APIs:** REST → GraphQL, HTTP/REST → gRPC, SOAP/legacy APIs → modern interfaces - **Authentication:** Legacy auth → OAuth/OIDC, SAML/SSO, modern identity and authorisation systems - **Repositories:** Polyrepo → monorepo using Bazel, Nx, Turborepo, or similar - **Testing:** Migration of unit, integration, browser, and E2E testing frameworks - **Dependencies/SDKs:** Replacement of deprecated or EOL libraries, APIs, runtimes, and vendor SDKs ## Ideal Background - **5+ years of professional software engineering experience**, ideally Senior, Staff, Principal, or equivalent. - Personally owned or made substantial technical contributions to **large-scale production migrations**. - Experience working with mature systems involving technical debt, complex dependencies, legacy integrations, and significant regression risk. - Strong knowledge of **compatibility, testing, observability, staged rollouts, rollback strategies, and behavioural equivalence**. - Ability to reason deeply about unfamiliar codebases and diagnose subtle migration failures. - **Especially valuable:** engineers who have modernised **core banking, payments, trading, insurance, healthcare, telecom, or other high-reliability systems**. - For **COBOL/mainframe modernisation, experience with technologies such as z/OS, CICS, JCL, DB2, VSAM, batch processing, and COBOL-to-Java/Python migrations** is particularly valuable. ## Why Join - Apply your migration expertise to help shape how **frontier AI models understand and execute complex software modernisation**. - Work on technically challenging problems modelled after **real-world, production-scale legacy systems**. - Contribute expertise developed from large enterprise migrations without needing an open-source maintainer background. - Opportunity for **ongoing work** as the research program expands.