Sometimes it becomes necessary to write your implementation of controllers using Spring Boot. For example, if you are not using REST, requests come to you from a non-standard communication channel. This article will describe how to create your custom annotation for request routing. I will be using Kotlin to demonstrate the use of functions in controllers. But nothing prevents you from using exactly the same approach in Java. suspend Creating an annotation ) @Target(AnnotationTarget.FUNCTION) @Retention(AnnotationRetention.RUNTIME) annotation class Route ( val value: RouteCommand, You can use an Enum or a REST-like string as a value, then use for parsing. AntPathMatcher Methods registration To register methods, we need to implement and scan all beans containing our annotation. Then put the parsed methods into a map. BeanPostProcessor instance = bean,
                    function = function,
                    inputType = inputType,
                    returnType = returnType,
                )
            }
        } } } MethodIntrospector.selectMethods<Route>(targetType) { } }
} ) @Component class RouteMethodRegistry : BeanPostProcessor { private val registry: MutableMap<RouteCommand, RouteMethod> = ConcurrentHashMap() fun resolveMethod (command: RouteCommand ) : RouteMethod = registry[command] ?: throw IllegalStateException( "No registered method for $command command" ) override fun postProcessAfterInitialization (bean: Any , beanName: String ) : Any { val targetClass = AopProxyUtils.ultimateTargetClass(bean) if (AnnotationUtils.isCandidateClass(targetClass, Route:: class .java)) { val methodAnnotations: Map<Method, Route> = getMethodsWithRouteAnnotation(targetClass) for ((method, annotation ) in methodAnnotations) { validateNoRegisteredMethods( annotation .value) val function = method.kotlinFunction ?: throw IllegalStateException( "Kotlin function for ${method.name} method is null" ) val (inputType, returnType) = parseTypes(function) registry[ annotation .value] = RouteMethod( return bean private fun parseTypes (function: KFunction <*>) : Pair<KClass<*>?, KClass<*>> { // The first element is the instance itself val inputParams = function.parameters.drop( 1 ) if (inputParams.size > 1 ) throw IllegalStateException( "Found ${inputParams.size} parameters for function $function . Please use 1 parameter" ) val inputType = inputParams.map { it.type.classifier as KClass<*>}.firstOrNull() val returnType = function.returnType.classifier!! as KClass<*> return inputType to returnType private fun getMethodsWithRouteAnnotation (targetType: Class <*>) : Map<Method, Route> = method -> AnnotatedElementUtils.getMergedAnnotation(method, Route:: class .java) private fun validateNoRegisteredMethods (command: RouteCommand ) { if (registry.containsKey(command)) throw IllegalStateException( "More than 1 methods use the same route ${command.name} " ) data class RouteMethod ( val instance: Any, val function: KFunction<*>, val inputType: KClass<*>?, val returnType: KClass<*>, In the method, the input and output parameters are extracted to then convert the data into them using the . parseTypes() objectMapper The method will be used later for routing requests. resolveMethod() Requests routing Then we need to implement the routing itself. In this example, when the method completes, we invoke the callback function. ) { callback.success(output) }
    } method.function.callSuspend(method.instance) method.function.callSuspend(method.instance, input) } }
} @Component class QueryRouter ( private val objectMapper: ObjectMapper, private val routeMethodRegistry: RouteMethodRegistry, fun route (query: String , callback: Callback ) = CoroutineScope(Dispatchers.Default).launch { try { val output = route(query) } catch (e: Exception) { callback.failure( 500 , e.message) private suspend fun route (query: String ) : String { val (command, input) = parseRouteParams(query) val method = routeMethodRegistry.resolveMethod(command) val output = if (method.inputType == null ) else return objectMapper.writeValueAsString(output) private fun parseRouteParams (query: String ) : Pair<RouteCommand, Any?> { TODO( "Implement according to your data format" ) In order for controller methods to be marked with the suspend keyword, we call functions via . callSuspend() You can use the standard to convert input and output data. The implementation of the method depends on the data format used. objectMapper parseRouteParams() Using annotations in controllers }
} @Controller class TestController { @Route(RouteCommand.TEST_CONTROLLER) suspend fun someMethod (request: MyRequest ) : MyResponse { delay( 1000 ) return MyResponse(request. data ) Now we can freely create methods in controllers that accept usable classes as input and return a response. All routing work will be done by our . QueryRouter

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