🧠 Product Filter – Specification Pattern in Java 21

This project demonstrates a clean and scalable implementation of the Specification Pattern in Java 21, applying the Open-Closed Principle (from the SOLID principles) to filter a dynamic product catalog of over 1500 items.

It’s built with Gradle, features functional composition (AND, NOT), and includes a dynamic, adaptive test suite using JUnit 5.

Post explaining patterns used

• Open/Closed - Specification Pattern

📦 Features

• ✅ Java 21 + Gradle
• ✅ Custom Specification<T> interface
• ✅ Dynamic filtering by:
  • Color
  • Size
  • Price thresholds
  • Stock availability
• ✅ Functional-style composition (AND / NOT)
• ✅ Fluent utility Specs builder
• ✅ 1500+ randomly generated products
• ✅ Adaptive and resilient unit tests with JUnit 5

---

📁 Project Structure

vendomita/
├── build.gradle
├── settings.gradle
├── README.md
├── src/
│   ├── main/
│   │   └── java/com/terabyte/specfilter/
│   │       ├── App.java
│   │       ├── model/
│   │       ├── spec/
│   │       └── util/
│   └── test/
│       └── java/com/terabyte/specfilter/
│           └── ProductFilterTest.java

---

🚀 How to Run

Requirements

• Java 21
• Gradle 8.x (or use the wrapper ./gradlew)

Build and Run

git clone https://github.com/darklatiz/vendomita.git
cd vendomita
./gradlew build
./gradlew test

The main app will generate 15000 random products and filter them using composed specifications (e.g., in stock AND price < 1000).

If you get a “no main class” error, make sure your build.gradle contains:

application {
    mainClass = 'com.terabyte.specfilter.App'
}

---

🧪 Running Tests

This project uses JUnit 5 with adaptive assertions (no hardcoded values) based on the generated data.

./gradlew test

All test cases will pass dynamically even as the dataset changes with every execution.

---

🧠 Why Specification Pattern?

This pattern helps you decouple business rules from filtering logic and supports:

• Composability (AND, OR, NOT)
• Testability (unit test each rule independently)
• Reusability (use rules in different contexts: APIs, batch, etc.)
• Extensibility (Open-Closed Principle in action)

Instead of writing dozens of filterByXAndYAndZ() methods, you can combine small specs dynamically.

---

📘 Example

Specification<Product> spec = Specs.and(
    new InStockSpecification(),
    new PriceLessThanSpecification(BigDecimal.valueOf(1000)),
    new SizeSpecification(Size.MEDIUM)
);

productFilter.filter(products, spec)
    .forEach(p -> System.out.println("MATCH: " + p.name()));

---

👨‍💻 Author

Laboratorios Terabyte Built with ❤️ by @darklatiz

---

📄 License

This project is licensed under the MIT License.