[JVM-Package] How I can get eval value for each iteration

Hi~I using xgboost4j-spark version0.82 in spark scala.
I use setCustomEval and fit my **classification model** successfully, and I can see the eval value for each iteration in console.
But I want to save the Eval Value for each iteration into file, hwo can I do?

Start by tracing the xgboost4j-spark setCustomEval and fit entry points that produce evaluation values in the console. Check how per-iteration values are currently exposed and whether the classification workflow has a documented output path. Done means identifying or documenting a supported way to persist each iteration's evaluation value.

Written by the indexing model from the issue text.