Give this a shot:
val person = Person("fred", 25)
val mapper = new ObjectMapper()
mapper.registerModule(DefaultScalaModule)
val out = new StringWriter
mapper.writeValue(out, person)
val json = out.toString()
println(json)
val person2 = mapper.readValue(json, classOf[Person])
println(person2)
EDIT
Just be sure to declare the Person
class as top level as it will not work otherwise.