Looking for a good example of deserializing polymorphic serialization using jackson with scala

Question

Looking for a good example of polymorphic serialization deserialization using jackson with scala

got an exception:

Exception in the stream "main" Blockquote org.codehaus.jackson.map.exc.UnrecognizedPropertyException: Unidentified field "animals" (zoo class) not marked as ignorant

by trying the following code:

import org.codehaus.jackson.annotate.{ JsonTypeInfo, JsonSubTypes } import org.codehaus.jackson.annotate.JsonSubTypes.Type @JsonTypeInfo( use = JsonTypeInfo.Id.NAME, include= JsonTypeInfo.As.PROPERTY, property = "type" ) @JsonSubTypes(Array( new Type(value= classOf[Cat] , name = "cat"), new Type(value= classOf[Dog] , name = "dog") ) ) abstract class Animal { val name:String = "NoName" } class Cat extends Animal{ val favoriteToy = "edi" } class Dog extends Animal{ val breed = "German Shepherd" val color = "brown" } class Zoo { val animals = new scala.collection.mutable.ListBuffer[Animal] } import org.codehaus.jackson.map.ObjectMapper object Foo { def main (args:Array[String]) { val mapper = new ObjectMapper() mapper.setPropertyNamingStrategy(CamelCaseNamingStrategy ) val source = scala.io.Source.fromFile("input.json" ) val input = source.mkString source.close val zoo = mapper.readValue(input,classOf[Zoo]) println(mapper.writeValueAsString(zoo)) } import org.codehaus.jackson.map.introspect.{AnnotatedField, AnnotatedMethod} import org.codehaus.jackson.map.{MapperConfig, PropertyNamingStrategy} object CamelCaseNamingStrategy extends PropertyNamingStrategy{ override def nameForGetterMethod (config: MapperConfig[_], method: AnnotatedMethod, defaultName: String) = { translate(defaultName) } override def nameForSetterMethod (config: MapperConfig[_], method: AnnotatedMethod, defaultName: String) = { translate(defaultName) } override def nameForField (config: MapperConfig[_], field: AnnotatedField, defaultName: String) = { translate(defaultName) } def translate(defaultName:String) = { val nameChars = defaultName.toCharArray val nameTranslated = new StringBuilder(nameChars.length*2) for ( c <- nameChars){ if (Character.isUpperCase(c)){ nameTranslated.append("_") } nameTranslated.append( Character.toLowerCase(c)) } nameTranslated.toString } } 

file input.json

 { "animals": [ {"type":"dog","name":"Spike","breed":"mutt","color":"red"}, {"type":"cat","name":"Fluffy","favoriteToy":"spider ring"} ] } 

Answer 1

If you are doing polymorphic deserialization in Scala, I highly recommend using the case classes and the Jackson Scala module.

 object Test { import com.fasterxml.jackson.annotation.JsonSubTypes.Type import com.fasterxml.jackson.annotation.{JsonSubTypes, JsonTypeInfo} import com.fasterxml.jackson.databind.ObjectMapper import com.fasterxml.jackson.module.scala.DefaultScalaModule import com.fasterxml.jackson.module.scala.experimental.ScalaObjectMapper @JsonTypeInfo( use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.PROPERTY, property = "type" ) @JsonSubTypes(Array( new Type(value = classOf[Cat], name = "cat"), new Type(value = classOf[Dog], name = "dog") )) trait Animal case class Dog(name: String, breed: String, leash_color: String) extends Animal case class Cat(name: String, favorite_toy: String) extends Animal case class Zoo(animals: Iterable[Animal]) def main(args: Array[String]): Unit = { val objectMapper = new ObjectMapper with ScalaObjectMapper objectMapper.registerModule(DefaultScalaModule) val dogStr = """{"type": "dog", "name": "Spike", "breed": "mutt", "leash_color": "red"}""" val catStr = """{"type": "cat", "name": "Fluffy", "favorite_toy": "spider ring"}""" val zooStr = s"""{"animals":[$dogStr, $catStr]}""" val zoo = objectMapper.readValue[Zoo](zooStr) println(zoo) // Prints: Zoo(List(Dog(Spike,mutt,red), Cat(Fluffy,spider ring))) } } 

Answer 2

Ok, here's a working example with scala based on Deserialize JSON with Jackson in Polymorphism by programmer Bruce :

 import org.codehaus.jackson.annotate.JsonSubTypes.Type import org.codehaus.jackson.annotate.{JsonSubTypes, JsonTypeInfo} @JsonTypeInfo( use = JsonTypeInfo.Id.NAME, include= JsonTypeInfo.As.PROPERTY, property = "type" ) @JsonSubTypes(Array( new Type(value= classOf[Cat] , name = "cat"), new Type(value= classOf[Dog] , name = "dog") ) ) abstract class Animal { var name:String ="" } class Dog extends Animal{ var breed= "German Shepherd" var color = "brown" } class Cat extends Animal{ var favoriteToy:String = "nothing" } class Zoo { var animals = new Array[Animal](5) } import org.codehaus.jackson.annotate.JsonAutoDetect.Visibility import org.codehaus.jackson.annotate.JsonMethod import org.codehaus.jackson.map.{DeserializationConfig, ObjectMapper} object Foo { def main (args:Array[String]) { val mapper = new ObjectMapper().setVisibility(JsonMethod.FIELD,Visibility.ANY) mapper.configure(DeserializationConfig.Feature.FAIL_ON_UNKNOWN_PROPERTIES,false) val source = scala.io.Source.fromFile("/input.json" ) val input = source.mkString println("input " + input) source.close val zoo = mapper.readValue(input,classOf[Zoo]) println(mapper.writeValueAsString(zoo)) } } 

file: input.json {"animals": [{"Type": "dog", "name": "Spike", "breed": "Fool", "color": "red"}, {"type": "cat", "name": "Fluffy", "favoriteToy": "spider ring"}]}