How to continue program if catch JsonParse error - json

Question

First of all - sorry for stupid question.
I got some Json string from DB and want to parse all of them with json4s:
val df = sqlContext.sql("SELECT * FROM analytic.test").repartition(22)
val df_base = df.map(f => {
implicit val formats = DefaultFormats
val jsonString = f(5).toString
val tempJSON = parse(jsonString)
val mainJsonArray = tempJSON \ "events"
(
f(2).toString,
makeEventArray(mainJsonArray)
)
}).cache()
All good, i got Json's, but sometimes in DB occurs some failed Json, that take me to error :
com.fasterxml.jackson.core.JsonParseException: Unexpected end-of-input: was expecting closing '"' for name
First question - How can I evade this row with corrupt Json and continue my program?
I trying surround parse with try\catch, but in this case:
var tempJSON = json4s.JsonAST.JValue
try {
tempJSON = parse(f(5).toString)
} catch {
case e: Exception => println("Error on JSON parser. " + e )
}
But taking error:
Error:(51, 25) type mismatch;
found: org.json4s.JValue (which expands to) org.json4s.JsonAST.JValue
required: org.json4s.JsonAST.JValue.type tempJSON = parse(f(5).toString)
^
Second question - How to declare tempJson right?
Or I must validate Json before parse? How?

Answer 1

You can use Try for it:
val tempJSON = Try(parse(f(5).toString))
So now, you can match it:
tempJSON match {
case Success(yourValue) => ???
case Failure(exception) => println(exception.getMessage)
}
Or, if you don't need the exception, you would convert it to Option:
tempJSON.toOption
You'll get None or Some(value).

Answer 2

I don't know json4s but it probably exists, like in Play Json, a validate function returning something like a JsError or a JsSuccess.
Otherwise, an other way to go is to return an Option[JValue] (if you don't want to deal with exceptions), i.e. :
def function: Option[JValue] = {
try {
Option(parse(f(5).toString))
} catch {
case e: Exception => None
}
}

Answer 3

If you want to catch all parsing errors and silently skip them, which is risky and ill advised in most cases.
You can simply do:
df.flatMap(f => Try(do something).toOption)
You may however prefer, earlier validation preventing this to begin with, catching a more specific error only, logging errors etc.