Reading YAML in Scala without 'case class' - scala

Question

I am trying to read YAML file from Scala and I am able to read the file using the code given below. One of the disadvantage I see here is the necessity for me to create case class to have a mapping with the YAML file I am using. Every time I change the content of YAML it becomes necessary for me to change the case class. Is there any way in Scala to read YAML with out the need for me to create the case class. (I have also used Python to read YAML ; where we do not have the constraint of mapping a Class with the YAML structure...and would like to do similar thing in Scala)
Note : When I add a new property in YAML and if my case class do not have a matching property I get UnrecognizedPropertyException
package yamlexamples
import com.fasterxml.jackson.dataformat.yaml.YAMLFactory
import com.fasterxml.jackson.databind.ObjectMapper
import com.fasterxml.jackson.module.scala.DefaultScalaModule
object YamlTest extends App{
case class Prop(country: String, state: List[String])
val mapper: ObjectMapper = new ObjectMapper(new YAMLFactory())
mapper.registerModule(DefaultScalaModule)
val fileStream = getClass.getResourceAsStream("/sample.yaml")
val prop:Prop = mapper.readValue(fileStream, classOf[Prop])
println(prop.country + ", " + prop.state)
}
sample.yaml(This works with code)
country: US
state:
- TX
- VA
sample.yaml (This throws Exception)
country: US
state:
- TX
- VA
continent: North America

Answer 1

You could parse the Yaml file and load it as a collections object instead of case case. But this comes at the cost of losing typesafety in your code. The Below code uses the load function supported by Yaml. Note that the load has overloaded methods to read from a inputstream/reader as well..
import scala.collection.JavaConverters._
val yaml = new Yaml()
val data = yaml.load(
"""
|country: US
|state:
| - TX
| - VA
|continent: North America
""".stripMargin).asInstanceOf[java.util.Map[String, Any]].asScala
Now data is a scala mutable collection instead of a case class
data: scala.collection.mutable.Map[String,Any] = Map(country -> US, state -> [TX, VA], continent -> North America)

Answer 2

You could parse the YAML file using Jackson or SnakeYaml. However, Jackson does not support references/anchors, while SnakeYaml does. So, it is better to parse the YAML file using SnakeYaml & access data elements with Jackson library
import java.io.{File, FileInputStream, FileReader}
import com.fasterxml.jackson.dataformat.yaml.YAMLFactory
import com.fasterxml.jackson.module.scala.DefaultScalaModule
import com.fasterxml.jackson.databind.{JsonNode, ObjectMapper}
import org.yaml.snakeyaml.Yaml
// Parsing the YAML file with SnakeYAML - since Jackson Parser does not support Anchors and references
val ios = new FileInputStream(new File(yamlFilePath))
val yaml = new Yaml()
val mapper = new ObjectMapper().registerModules(DefaultScalaModule)
val yamlObj = yaml.loadAs(ios, classOf[Any])
// Converting the YAML to Jackson YAML - since it has more flexibility
val jsonString = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(yamlObj) // Formats YAML to a pretty printed JSON string - easy to read
val jsonObj = mapper.readTree(jsonString)
Finally, you get the JsonNode object, which enables us to convert to other datatypes.