Building Rule-Validator: Why I Built a Java Annotation-Based Rule Engine After 3 Years of Fighting Business Rules

Building Rule-Validator: Why I Built a Java Annotation-Based Rule Engine After 3 Years of Fighting Business Rules Let me tell you a story. For three years, I've been fighting the same battle in enterprise Java development: business rule validation . Honestly, every time a new requirement comes in like "this order must be approved if amount > 10000 AND user level > 3 AND discount < 0.1", I'd end up with a 500-line method full of if-else that nobody wants to touch. Sound familiar? I tried every existing solution: Drools: Too heavy, requires learning a new DSL, impossible to debug Spring Validation: Great for basic validation, but can't handle complex business rules nicely Hand-written if-else: Works, but becomes unreadable after 10 rules Expression engines like Aviator: Still externalized, breaks compile-time checking So here's the thing — I learned the hard way that what Java developers actually want is simple, annotation-based, compile-safe rule validation that lives right next to your code. That's why I built rule-validator . What is Rule-Validator? Rule-validator is a lightweight Java library that lets you define business rules using annotations directly on your classes . No DSL, no external files, no magic — just simple, testable, maintainable rules. The core idea is: Each rule is a method annotated with @Rule Rules can be grouped and ordered You get full Java compile-time checking Everything stays in your code, where it belongs Here's a quick example to show you how it works: import com.github.kevinten10.rulevalidator.annotation.Rule ; import com.github.kevinten10.rulevalidator.annotation.RuleGroup ; import com.github.kevinten10.rulevalidator.core.RuleExecutor ; import com.github.kevinten10.rulevalidator.result.RuleResult ; // Define your business object public class Order { private BigDecimal amount ; private Integer userLevel ; private BigDecimal discount ; // getters and setters public BigDecimal getAmount () { return amount ; } public Integer getUserLevel ()