How can I convert a nested HashMap, nested with hashmaps, to json in Scala?

Question

My current hashmap looks like this:

val h1 = HashMap[String,Object]()
val h2 = ListBuffer[HashMap[String,String]]()
val h3 = HashMap[String,Object]()
val h4 = ListBuffer[HashMap[String,String]]()

Basically h1 is my main hash, with keys to h2 and h3 and other strings. h3 has keys to h4 and other strings.

Because scala doesn't support hash to json of string->object type, I've seen I had to write my old write/read methods

How can I write the write and read methods such that it detects the inner maps,lists?

I've been following this so far: Scala to JSON in Play Framework 2.1

From Dima's suggestion on using Jackson, getting error when tying it in with Play

play.api.UnexpectedException: Unexpected exception[RuntimeException: java.lang.VerifyError: class com.fasterxml.jackson.module.scala.ser.ScalaIteratorSerializer overrides final method withResolved.(Lcom/fasterxml/jackson/databind/BeanProperty;Lcom/fasterxml/jackson/databind/jsontype/TypeSerializer;Lcom/fasterxml/jackson/databind/JsonSerializer;)Lcom/fasterxml/jackson/databind/ser/std/AsArraySerializerBase;]
at play.api.http.HttpErrorHandlerExceptions$.throwableToUsefulException(HttpErrorHandler.scala:276)
at play.api.http.DefaultHttpErrorHandler.onServerError(HttpErrorHandler.scala:206)
at play.api.GlobalSettings$class.onError(GlobalSettings.scala:160)
at play.api.DefaultGlobal$.onError(GlobalSettings.scala:188)
at play.api.http.GlobalSettingsHttpErrorHandler.onServerError(HttpErrorHandler.scala:98)
at play.core.server.netty.PlayRequestHandler$$anonfun$2$$anonfun$apply$1.applyOrElse(PlayRequestHandler.scala:100)
at play.core.server.netty.PlayRequestHandler$$anonfun$2$$anonfun$apply$1.applyOrElse(PlayRequestHandler.scala:99)
at scala.concurrent.Future$$anonfun$recoverWith$1.apply(Future.scala:344)
at scala.concurrent.Future$$anonfun$recoverWith$1.apply(Future.scala:343)
at scala.concurrent.impl.CallbackRunnable.run(Promise.scala:32)

Caused by: java.lang.RuntimeException: java.lang.VerifyError: class com.fasterxml.jackson.module.scala.ser.ScalaIteratorSerializer overrides final method withResolved.(Lcom/fasterxml/jackson/databind/BeanProperty;Lcom/fasterxml/jackson/databind/jsontype/TypeSerializer;Lcom/fasterxml/jackson/databind/JsonSerializer;)Lcom/fasterxml/jackson/databind/ser/std/AsArraySerializerBase;
at play.api.mvc.ActionBuilder$$anon$2.apply(Action.scala:463)
at play.api.mvc.Action$$anonfun$apply$2$$anonfun$apply$5$$anonfun$apply$6.apply(Action.scala:112)
at play.api.mvc.Action$$anonfun$apply$2$$anonfun$apply$5$$anonfun$apply$6.apply(Action.scala:112)
at play.utils.Threads$.withContextClassLoader(Threads.scala:21)
at play.api.mvc.Action$$anonfun$apply$2$$anonfun$apply$5.apply(Action.scala:111)
at play.api.mvc.Action$$anonfun$apply$2$$anonfun$apply$5.apply(Action.scala:110)
at scala.Option.map(Option.scala:146)
at play.api.mvc.Action$$anonfun$apply$2.apply(Action.scala:110)
at play.api.mvc.Action$$anonfun$apply$2.apply(Action.scala:103)
at scala.concurrent.Future$$anonfun$flatMap$1.apply(Future.scala:251)

Caused by: java.lang.VerifyError: class com.fasterxml.jackson.module.scala.ser.ScalaIteratorSerializer overrides final method withResolved.(Lcom/fasterxml/jackson/databind/BeanProperty;Lcom/fasterxml/jackson/databind/jsontype/TypeSerializer;Lcom/fasterxml/jackson/databind/JsonSerializer;)Lcom/fasterxml/jackson/databind/ser/std/AsArraySerializerBase;
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClass(ClassLoader.java:763)
at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
at java.net.URLClassLoader.defineClass(URLClassLoader.java:467)
at java.net.URLClassLoader.access$100(URLClassLoader.java:73)
at java.net.URLClassLoader$1.run(URLClassLoader.java:368)
at java.net.URLClassLoader$1.run(URLClassLoader.java:362)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:361)
at java.lang.ClassLoader.loadClass(ClassLoader.java:424)

My dependencies:

libraryDependencies += "com.fasterxml.jackson.core" % "jackson-databind" % "2.4.4"
libraryDependencies += "com.fasterxml.jackson.module" %% "jackson-module-scala" % "2.5.1"

Answer 1

Who told you scala does not support it? There are different kinds of libraries ... for example, if you use Jackson, you'd just need to do something like this:

 val mapper = new ObjectMapper()
   .registerModule(DefaultScalaModule)

 val h1 = mapper.readObject(input, classOf[Map[String,_]])