java generics in scala sometimes fail with cast exception - scala

Question

So this is a pretty specific problem, but might be related to issues other may have experience, though I could not find a good solution.
in our specific case, we are using Elasticsearch. the problematic piece of code is this:
val hit: org.elasticsearch.search.SearchHit = {...}
val innerSystemField: Option[Long] =
Try(hit.field("system.innerField").getValue) match {
case Success(x) => Some(x.asInstanceOf[Long])
case Failure(e) => {
logger.error("exception during innerField retrieval", e)
None
}
}
so, it doesn't really matters we are using Elasticsearch, what matter, is the library API. so, here's the SearchHit interface's field method which returns an instance of SearchHitField. and here's the SearchHitField interface's getValue method. the method is declared as:
<V> V getValue();
and this is where the problem lies. the mapping which we defined Elasticsearch with, guarantee that the returned value will always be a Long. but every once in a while we get a Failure containing a java.lang.ClassCastException: java.lang.Long cannot be cast to scala.runtime.Nothing$. The thing is, that if I explicitly write the type, it won't compile:
[error] /home/me/projects/my-project/src/main/scala/com/org/project/MyElasticsearchCode.scala:123: polymorphic expression cannot be instantiated to expected type;
[error] found : [V]()V
[error] required: Long
[error] Try[Long](hit.field("system.innerField").getValue) match {
[error] ^
[error] one error found
[error] (project/compile:compileIncremental) Compilation failed
[error] Total time: 4 s, completed Jul 27, 2015 4:16:41 PM
So how do I get around this problem?

Answer 1

I find the message of the ClassCastException a bit confusing. Maybe you could try this:
val innerSystemField: Option[Long] =
Try[Any](hit.field("system.innerField").getValue) match {
case Success(x: java.lang.Long) => Some(x.asInstanceOf[Long])
case Failure(e) => {
logger.error("exception during innerField retrieval", e)
None
}
}