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LegacyLift: Safe Java Modernization
PROBLEM Thousands of business-critical applications still run on Java 8 and Spring Boot 2, versions that no longer receive free security updates. Everyone knows they should upgrade, but teams keep postponing it: the original authors are gone, documentation is stale, tests are thin, and one small change can silently break behaviour in production. Migration work is slow, expensive and error-prone. SOLUTION LegacyLift is an agentic modernization workflow powered by IBM Bob in agent mode. It turns an upgrade into four verifiable steps: 1. Explain: Bob reads the whole repository and writes an architecture report: module map, dependency diagram, request flow, migration inventory, risk list and test gaps. 2. Protect: before any change, Bob writes characterization tests that lock in what the code does today. 3. Migrate: Bob upgrades the code on a separate branch under one strict rule: no test assertion may be changed. 4. Prove: all tests run again on the new version. Passing tests mean behaviour was preserved, not that tests were adjusted. RESULTS (Spring PetClinic, a real open-source app) - Java 8 to Java 21, Spring Boot 2.7.3 to 3.4.5 - Tests 41 to 71 (30 characterization tests written by Bob); branch coverage of the critical Owner and PetValidator classes raised to 100% - 14 files migrated from javax to jakarta - All 71 tests run on Java 21 with 0 failures - 1.7 hours end to end, versus an estimated 24 hours of manual work (about 93% less time) We verified independently that test logic is identical before and after migration. Human review also caught mistakes in Bob's first analysis (it missed 4 of 14 files); we fixed the prompt and documented the corrections. Trust the agent, verify with evidence. TARGET USERS AND HOW THEY USE IT Developers and teams maintaining legacy Java/Spring systems. They open their repository in IBM Bob and run the versioned prompts in order (PROMPTS.md for PetClinic, PROMPTS_TEMPLATE.md for any Java/Spring project), reviewing each report before the next step. A Streamlit dashboard shows the results: KPIs, coverage and effort charts, all reports, and a Bob Evidence tab with every Bob session. WHAT MAKES IT UNIQUE Most AI migration tools just rewrite code. LegacyLift makes the agent write the safety net first, forbids it from touching that safety net, and produces evidence (reports, coverage, test diff checks, metrics) that the result behaves like the original. It also keeps a human-in-the-loop checkpoint after every step. COMPANION TOOL We also packaged the mechanical steps into LegacyLift Converter: upload a legacy project zip and download it migrated with a test-verified report (OpenRewrite plus fixes learned in this project). For transparency, the converter was built with Claude Code, not IBM Bob; all analysis, tests, migration, reports and the dashboard were done with IBM Bob.
27 Sep 2026
