CODESAMPLE
Chain of Responsibility - Kotlin
The Chain of Responsibility is a behavioral pattern that allows you to pass a request along a chain of handlers. Each handler decides either to process the request or to pass it to the next handler in the chain. This decouples the sender of a request from its receivers, giving multiple objects the opportunity to handle it without the sender explicitly knowing who’s handling it.
My Kotlin implementation uses an abstract Handler class with a nextHandler property. Concrete handlers (like AuthHandler, LoggingHandler, and BusinessLogicHandler) inherit from this, and either process the request if they can, or call nextHandler?.handle(request) to pass it along. An explicit chain is built in the main function. This approach leverages Kotlin’s concise syntax, class delegation, and nullable types for a clean and type-safe implementation.
abstract class Handler {
protected var nextHandler: Handler? = null
abstract fun handle(request: String): String
fun setNext(handler: Handler): Handler {
nextHandler = handler
return handler
}
}
class AuthHandler : Handler() {
override fun handle(request: String): String {
if (request == "invalid") {
return "Authentication failed"
}
return nextHandler?.handle(request) ?: request
}
}
class LoggingHandler : Handler() {
override fun handle(request: String): String {
println("Logging request: $request")
return nextHandler?.handle(request) ?: request
}
}
class BusinessLogicHandler : Handler() {
override fun handle(request: String): String {
if (request.startsWith("process")) {
return "Business logic processed: $request"
}
return nextHandler?.handle(request) ?: request
}
}
fun main() {
val chain = AuthHandler()
.setNext(LoggingHandler())
.setNext(BusinessLogicHandler())
println(chain.handle("valid request"))
println(chain.handle("invalid"))
println(chain.handle("process data"))
println(chain.handle("other request"))
}