This is a basic currency exchange rate API that displays aspect oriented programming used for logging and data access operations.

• Logged - used to annotate the functions that will be intercepted by LogAspect
• DataAccess - used to annotate the functions that will be intercepted by DataAccessAspect

• LogAspect
  • Intercepts function calls to functions annotated with @Logged. These functions will trigger a log-call before and after function execution (provided function did not throw an exception) with the log level specified in the annotations field value logLevel.
• DataAccessAspect
  • Intercepts function calls to functions annotated with @DataAccess. These functions will wrap the function call in a try/catch, transforming the potential SQL-related exceptions to a custom one along with a KFunction<*> object. This object is used to find the relevant error message for the given function that failed in the error messages resource bundle.

Clone repository, start application from src/main/kotlin/no/esa/aop/application/AopApplication.main.

1. Build & run application in your IDE.
2. View the Swagger-UI in a browser
3. Try the requests in the exchange-rate-controller.
4. To see how errors are handled, throw a few Exceptions in functions annotated with @DataAccess.

This is called 'around' every function annotated with @DataAccess. joinPoint.proceed() calls the intercepted function. Any exception is immediately mapped to a DataAccess exception, which is picked up by /resource/ExceptionHandler.kt.

@Aspect
@Component
class DataAccessAspect {

	@Around("@annotation(no.esa.aop.annotation.DataAccess)")
	fun dataAccessOperation(joinPoint: ProceedingJoinPoint): Any? {
		val kFunction = getKFunction(joinPoint)

		return try {
			joinPoint.proceed()
		} catch (error: Exception) {
			getLogger(joinPoint).error(error.message)

			if (kFunction != null) {
				throw DataAccessException(kFunction, error)
			} else throw error
		}
	}
}

Abstracting away error handling from virtually identical functions improves readability.

@DataAccess
@Logged(APIType.DATA_ACCESS, LogLevel.INFO)
override fun getAll(): List<CurrencyEntity> {
	val query = QueryFileReader.readSqlFile(::getAll)

	return jdbcTemplate.query(query) { rs, _ ->
		CurrencyEntity(rs.getInt(PRIMARY_KEY), rs.getString(SYMBOL))
	}
}

This aspect inspects the function signature and return value and logs the events in a clean format to the console & to file. The log level and api type are optional parameters that can be defined per function.

@Target(AnnotationTarget.FUNCTION)
@Retention(AnnotationRetention.RUNTIME)
annotation class Logged(val apiType: APIType = APIType.INTERNAL,
			val logLevel: LogLevel = LogLevel.DEBUG)