Strangler Fig Pattern — Context-based Migration (Java)

This project demonstrates a context-based migration strategy using the Strangler Fig Pattern in Java with Gradle.

Instead of replacing the entire legacy codebase at once, this approach wraps existing code with a context-aware facade and incrementally routes new functionality into separate, isolated action classes.

---

Core Idea

• Context-aware class routing
• Legacy functionality remains untouched
• New functionality implemented as Action classes
• ContextFactory dynamically provides the correct implementation

---

Project Structure

src/java/
│
├── MyClass.java               → Legacy Entry Point
├── MyClassContext.java        → Context Interface for Routing
├── MyClassContextFactory.java → Factory for Context Decision
│
├── Action/
│   ├── Method1Action.java     → New Implementation of Method1
│   └── Method2Action.java     → New Implementation of Method2
│
├── Value.java / ValueMap.java → Supporting Data Objects
└── Main.java                  → Application Entry Point

---

How it works

// Example inside MyClass.java

MyClassContext context = MyClassContextFactory.create(valueMap);

context.method1();
context.method2();

• Old logic stays in MyClass
• New logic grows in Action classes
• Context Factory decides dynamically which implementation to use

---

Build & Run

Build

./gradlew build

Run

./gradlew run

Test

./gradlew test

---

Benefits of this Approach

• Minimal risk during migration
• Legacy & New Code co-exist
• Easy to test new features independently
• Clean separation of concerns
• Scalable migration strategy

---

License

Apache License, Version 2.0 [https://www.apache.org/licenses/LICENSE-2.0.txt]

Author

Matthis Burger — [info@burger-it.de]