Java Engineer – Application / Database Modernization (Freelancer)

Mactores is looking for a Software Engineer with proficiency in Java, Spring, and Hibernate to participate in the migration project from Oracle to PostgreSQL. The ideal candidate should possess a robust understanding of Java, Spring, and Hibernate, with hands-on experience in developing large-scale Java web applications.

What you will do?

• Analyze and remediate large enterprise Java codebases to replace legacy or database-specific SQL constructs with modern, standards-compliant SQL.
• Convert embedded SQL within Java services and MyBatis XML mappers, including rewriting constructs such as vendor-specific functions, sequences, pagination logic, dynamic SQL, and error-handling patterns.
• Collaborate closely with schema and database migration engineers to ensure application-layer SQL aligns with the modernized target schema.
• Refactor Java transaction logic, error-handling, drivers, and ORM/DAO layers to support the behavior of modern databases.
• Participate in unit, integration, and performance testing to confirm functional parity and ensure applications meet performance SLAs post-modernization.
• Support application cutover activities for production environments, including validation, monitoring setup, rollback planning, and stabilization.
• Produce engineering documentation: SQL remediation guides, code-migration runbooks, troubleshooting guides, and knowledge-transfer material for customer teams.
• Work across distributed teams (US & India) and collaborate with customer SMEs to ensure business logic alignment and successful modernization outcomes.

What are we looking for?

• Bachelor’s degree in Computer Science, Engineering, or related field.
• 3+ years of professional Java development experience (Spring, JDBC, MyBatis/Hibernate or equivalent).
• Experience with application modernization, database migrations, or large-scale refactoring initiatives.
• Strong SQL expertise and the ability to analyze, interpret, optimize, and rewrite complex SQL used within Java applications.
• Deep understanding of JDBC, ORMs, Java transaction patterns, and database-driven application flows.
• Experience working on enterprise-grade, high-performance applications with complex data interactions.
• Strong communication skills and ability to work with global distributed teams in US time-zones.

You will be preferred if

• Experience with PostgreSQL, Aurora PostgreSQL, or modernization from legacy databases such as Oracle, SQL Server, or DB2.
• Exposure to automated code-refactoring tools or GenAI-assisted remediation workflows.
• Familiarity with CI/CD environments, performance testing tools, and observability stacks.
• Consulting or professional services experience delivering fixed-timeline modernization projects.