Scala : Retry with try/catch for exception handling - json

Question

I am trying to add a retry logic for JSON conversion. When converting an object to json, I am retrying for 3 times if there is any exception. I am doing :
var mapper = new ObjectMapper() with ScalaObjectMapper
intializeMapper( )
def intializeMapper() = {
// jackson library does not support seralization and deserialization of
// of scala classes like List and Map, this is needed to support it
mapper.registerModule( DefaultScalaModule )
// enables parsing of NaN. Enabling it here as JsonUtil class currently in
// use supports it.
mapper.configure(JsonParser.Feature.ALLOW_NON_NUMERIC_NUMBERS, true )
mapper.setSerializationInclusion(Include.NON_NULL)
mapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false)
}
def getPersonRDD(result: DataFrame): RDD[(String, String)] = {
val finalValue = result.rdd.map({
r =>
val customerId = r.getAs[String](CUSTOMER_ID)
val itemId = r.getAs[Map[String, Int]](ITEM_ID)
val itemName = r.getAs[Map[String, Int]](ITEM_NAME)
val person = Person(itemId, itemName)
val jsonString = toJson(person)
(customerId, jsonString)
})
return finalValue
}
def fromJson(json: String, clazz: Class[_]) = {
mapper.readValue(json, clazz)
}
def toJson(value: Any): String = {
var jsonString: String = " "
jsonString = mapper.writeValueAsString(value)
try {
fromJson(jsonString, clazz)
return jsonString
} catch {
case Exception => {
publishMetrics(PARSING_EXCEPTION, 1.0)
val result = util.Try(retry() {
jsonString = mapper.writeValueAsString(value)
val features = fromJson(jsonString, clazz)
})
result match {
case util.Success(value) => jsonString
case util.Failure(error) => {
log.error("Error while parsing JSON " + jsonString)
return jsonString
}
}
}
}
}
// Returning T, throwing the exception on failure
#annotation.tailrec
def retry[T](n: Int = 3)(fn: => T): T = {
util.Try {
fn
} match {
case util.Success(x) => x
case _ if n > 1 => retry(n - 1)(fn)
case util.Failure(e) => throw e
}
}
case class Person(itemId: Map[String, Int], itemName: Map[String, Int]) extends Serializable
Is this correct ? I am new to Scala. Can someone suggest me if there is any better way for achieving this ? Is there predefined retry logic available in Scala ? The reason I am trying to add retry logic for JSON conversion is due to Jackson version I use(which I can't change for now), sometimes my writeValueAsString results in incomplete JSON.

Answer 1

You retry function seems correct. The only flaw I can think of is that if you expect something would fail it's better just make the return type Try[T], so you can handle it outside in the scala way.
Here is one of my implementation:
def retry[T](n: Int)(block: => T): Try[T] = {
val stream = Stream.fill(n)(Try(block))
stream find (_.isSuccess) getOrElse stream.head
}