OpenRewrite — Automated Mass Refactoring for Source Code

Introduction

OpenRewrite is an automated refactoring engine that applies deterministic transformations to source code at scale. It parses code into a lossless semantic tree (LST) preserving formatting and whitespace, then applies composable recipes to migrate frameworks, fix vulnerabilities, or upgrade language versions.

What OpenRewrite Does

• Migrates Java applications between major versions (Java 8 to 17, 17 to 21)
• Upgrades framework dependencies such as Spring Boot, JUnit, and Jakarta EE
• Applies security patches by replacing vulnerable API calls and dependencies
• Enforces coding standards and style rules across repositories
• Transforms build files (Maven POM, Gradle) alongside source code

Architecture Overview

OpenRewrite operates on a Lossless Semantic Tree (LST) that retains every character of the original file. Parsers convert source into LSTs, then recipes — composed of visitors — traverse and modify the tree. The printer serializes the LST back to text with minimal diff. Recipes are distributed as Maven artifacts and can be composed into migration plans.

Self-Hosting & Configuration

• Runs as a Maven or Gradle build plugin with no separate server required
• Configure active recipes and styles in pom.xml or build.gradle
• Recipe modules are pulled from Maven Central as regular dependencies
• The rewrite.yml file allows custom recipe composition and parameter overrides
• Moderne CLI provides optional commercial multi-repo orchestration

Key Features

• Lossless Semantic Tree preserves original formatting after transformations
• Pre-built recipes covering Java, Kotlin, Groovy, XML, YAML, and properties files
• Composable recipes — combine visitors into large migration plans
• Dry-run mode previews changes as diffs before applying
• Type-aware refactoring resolves method signatures, imports, and class hierarchies

Comparison with Similar Tools

• Error Prone — Catches bugs at compile time; OpenRewrite applies fixes across entire repos
• Refaster — Template-based refactoring in a single build; OpenRewrite supports cross-repo distribution
• Semgrep — Pattern-based linting; OpenRewrite uses a full semantic tree for type-aware transforms
• jscodeshift — JavaScript AST transforms; OpenRewrite targets JVM languages with format preservation

FAQ

Q: Does OpenRewrite modify code in place? A: Yes, rewriteRun applies changes directly. Use rewriteDryRun to generate a diff report first.

Q: Can I write custom recipes? A: Yes. Recipes are Java classes extending visitor patterns on the LST. You can also compose existing recipes in YAML.

Q: Does it support languages beyond Java? A: It has parsers for Kotlin, Groovy, XML, YAML, JSON, and properties files.

Q: Will it break my formatting? A: The LST preserves original formatting. Transformations only change targeted code.

Sources

• https://github.com/openrewrite/rewrite
• https://docs.openrewrite.org