[SpringIO2022] Major Migrations Made Easy with OpenRewrite
Tim te Beek’s Spring I/O 2022 session introduced OpenRewrite, a powerful tool for automating large-scale Java migrations. As a Java consultant at JDriven, Tim shared his passion for updating outdated technology stacks, using OpenRewrite to streamline upgrades across frameworks, libraries, and languages. His talk, delivered on his birthday, combined a compelling narrative with a live demo, showcasing how OpenRewrite transforms tedious migrations into quick, safe operations.
The Migration Challenge: Keeping Up with Open Source
Tim opened with a decade-long perspective on Java and Spring evolution, from Spring Framework 2.5 in 2009 to Java 17 and Spring Boot 2 in 2022. Each release—Java 8’s lambdas, Spring Boot’s reduced boilerplate, JUnit 5, or Java 11’s JAX-B dependencies—introduced valuable features but required manual upgrades across multiple services. Vulnerabilities like Log4Shell further necessitate rapid migrations, often under pressure. For large organizations with thousands of services, manual updates are impractical, making automation essential.
OpenRewrite addresses this by leveraging an abstract syntax tree (AST) to perform precise, safe refactorings. Unlike simple search-and-replace, it understands code context, preserving formatting and ensuring functional integrity. Tim emphasized its ability to handle migrations like JUnit 4 to 5, Log4j to SLF4J, or Spring Boot 1 to 2, reducing technical debt in minutes.
How OpenRewrite Works: Recipes and AST Magic
OpenRewrite’s core strength lies in its recipe-based approach. Recipes are modular, reusable transformations—implemented as Java visitors—that modify the AST. Tim explained how recipes range from simple (changing imports) to complex (converting JUnit 4’s expected exceptions to JUnit 5’s assertThrows). These can be combined into modules for tasks like framework upgrades or style enforcement. The tool supports Java, Groovy, YAML, and XML, enabling changes to Maven/Gradle builds and Spring configurations.
A key differentiator is OpenRewrite’s type attribution and format preservation, ensuring changes blend seamlessly with existing code. Tim’s demo illustrated this by migrating a Spring Pet Clinic project from Spring Boot 1.5 (Java 8) to Spring Boot 2.5 (Java 17). Using Maven’s OpenRewrite plugin, he applied recipes to update dependencies, imports, annotations, and properties, completing the migration in under 15 seconds per step, with only two minor test failures requiring manual fixes.
Spring Boot Migrator: Enhancing OpenRewrite
Tim introduced Spring Boot Migrator, an experimental Spring project built on OpenRewrite, designed to simplify migrations to Spring Boot. Initiated by VMware Labs in 2020 and led by Fabian Krüger, it offers an opinionated API for Spring-specific migrations, such as Java EE to Spring or NetWeaver to Spring Integration. Unlike OpenRewrite’s fully automated recipes, Spring Boot Migrator provides an interactive workflow, generating HTML reports to guide developers through component identification and transformation steps.
Looking ahead, Spring Boot Migrator aims to support Spring Framework 6 and Spring Boot 3, expected in November 2022, and facilitate cloud migrations to GraalVM. Tim encouraged community contributions, noting its role in easing enterprise migrations for VMware customers.
Impact and Community: Scaling Automation
OpenRewrite’s open-source model, backed by Moderne, ensures all recipes are Apache-licensed, fostering community-driven development. Tim highlighted its use in fixing static analysis issues (e.g., Checkstyle, Sonar), enforcing code style, and contributing to open-source projects like WireMock and Apache Maven. He shared his experience migrating thousands of unit tests, urging attendees to explore OpenRewrite’s web interface (app.moderne.io) and contribute recipes.
Tim’s talk inspired developers to embrace automation, reducing migration pain and enabling focus on innovation. His enthusiasm for OpenRewrite’s potential to transform development workflows resonated strongly with the audience.