mongodb - How to serialize a Scala Collection List into json using Gson lib -


i have class named inbox contains int , list of messages. message class.

the problem want store objects of inbox class in mongodb. have serialize these objects using gson, throws exception on deserialization.

java.lang.runtimeexception: failed invoke public scala.collection.immutable.list() no args

here inbox class :

@serialversionuid(1) class inbox(val uuid: int, var messagelist: listbuffer[message]) extends serializable {   adduuidtolist(uuid)          /*    * auxiliary constructor    */   def this() {     this(0, listbuffer[message]())   }    def addtomessagelist(addmessage: message) = {     messagelist += addmessage   }    var idlist = new mutablelist[int]()    def adduuidtolist(uuid : int)  = {     idlist += uuid      }    /*    * getters    */   def getuuid: int = uuid    /*    * returns sorted list based on datetime attribute of message class    */   def getmessagelist : listbuffer[message] = {     //var sortedlist = messagelist.sorted     messagelist   }    def getuuidslist: mutablelist[int] = idlist }

and message class :

class message(   val uuid: int,   val subject: string,   val body: string,    var artworkuuid: int,   val datetime: localdatetime = localdatetime.now() ) extends ordered[message] serializable

my test application :

object test extends app {   val inbox = new inbox(333,messagelist)    val gson = new gson()   val g = gson.tojson(inbox)   println(g + " converting json")   var inboxobj = gson.fromjson(g, classof[inbox])   println("message object returned " + inboxobj)    }

the output printed on console :

{"uuid":333,"messagelist":{"scala$collection$mutable$listbuffer$$start":{},"last0":{"head":{"uuid":321,"subject":"subject1","body":"bodytext1","artworkuuid":101,"datetime":{"date":{"year":2015,"month":7,"day":14},"time":{"hour":11,"minute":6,"second":51,"nano":579000000}},"readstatusint":0,"delete":{"deletestatusint":1,"deletereasonint":1}},"tl":{}},"exported":false,"len":2},"idlist":{"first0":{"elem":333,"next":{}},"last0":{"elem":333,"next":{}},"len":1}}converting  json [error] (run-main-0) java.lang.runtimeexception: failed invoke public scala.collection.immutable.list() no args java.lang.runtimeexception: failed invoke public scala.collection.immutable.list() no args     @ com.google.gson.internal.constructorconstructor$3.construct(constructorconstructor.java:107)     @ com.google.gson.internal.bind.reflectivetypeadapterfactory$adapter.read(reflectivetypeadapterfactory.java:186)     @ com.google.gson.internal.bind.reflectivetypeadapterfactory$1.read(reflectivetypeadapterfactory.java:103)     @ com.google.gson.internal.bind.reflectivetypeadapterfactory$adapter.read(reflectivetypeadapterfactory.java:196)     @ com.google.gson.internal.bind.reflectivetypeadapterfactory$1.read(reflectivetypeadapterfactory.java:103)     @ com.google.gson.internal.bind.reflectivetypeadapterfactory$adapter.read(reflectivetypeadapterfactory.java:196)     @ com.google.gson.gson.fromjson(gson.java:810)     @ com.google.gson.gson.fromjson(gson.java:775)     @ com.google.gson.gson.fromjson(gson.java:724)     @ com.google.gson.gson.fromjson(gson.java:696)     @ testactor$.delayedendpoint$testactor$1(testactor.scala:307)     @ testactor$delayedinit$body.apply(testactor.scala:54)     @ scala.function0$class.apply$mcv$sp(function0.scala:40)     @ scala.runtime.abstractfunction0.apply$mcv$sp(abstractfunction0.scala:12)     @ scala.app$$anonfun$main$1.apply(app.scala:76)     @ scala.app$$anonfun$main$1.apply(app.scala:76)     @ scala.collection.immutable.list.foreach(list.scala:383)     @ scala.collection.generic.traversableforwarder$class.foreach(traversableforwarder.scala:35)     @ scala.app$class.main(app.scala:76)     @ testactor$.main(testactor.scala:54)     @ testactor.main(testactor.scala)     @ sun.reflect.nativemethodaccessorimpl.invoke0(native method)     @ sun.reflect.nativemethodaccessorimpl.invoke(nativemethodaccessorimpl.java:62)     @ sun.reflect.delegatingmethodaccessorimpl.invoke(delegatingmethodaccessorimpl.java:43)     @ java.lang.reflect.method.invoke(method.java:497) caused by: java.lang.instantiationexception     @ sun.reflect.instantiationexceptionconstructoraccessorimpl.newinstance(instantiationexceptionconstructoraccessorimpl.java:48)     @ java.lang.reflect.constructor.newinstance(constructor.java:422)     @ com.google.gson.internal.constructorconstructor$3.construct(constructorconstructor.java:104)     @ com.google.gson.internal.bind.reflectivetypeadapterfactory$adapter.read(reflectivetypeadapterfactory.java:186)     @ com.google.gson.internal.bind.reflectivetypeadapterfactory$1.read(reflectivetypeadapterfactory.java:103)     @ com.google.gson.internal.bind.reflectivetypeadapterfactory$adapter.read(reflectivetypeadapterfactory.java:196)     @ com.google.gson.internal.bind.reflectivetypeadapterfactory$1.read(reflectivetypeadapterfactory.java:103)     @ com.google.gson.internal.bind.reflectivetypeadapterfactory$adapter.read(reflectivetypeadapterfactory.java:196)     @ com.google.gson.gson.fromjson(gson.java:810)     @ com.google.gson.gson.fromjson(gson.java:775)     @ com.google.gson.gson.fromjson(gson.java:724)     @ com.google.gson.gson.fromjson(gson.java:696)

maybe problem listbuffer convert before java.util list, try code:

import scala.collection.javaconverters._ import scala.collection.mutable.listbuffer import com.google.gson.gson import java.util.arraylist import java.lang.reflect.type import com.google.gson.reflect.typetoken   object gsoninscala extends app {     var id=4    var fruits = new listbuffer[string]()    fruits += "apple"   fruits += "banana"   fruits += "orange"     val tmp : inbox = inbox(id, fruits)    val json = tmp.tojson()    println("object2json: " + json)  }  import scala.collection.javaconversions._ import scala.collection.mutable.listbuffer import com.google.gson.gson import java.util.arraylist import com.google.gson.annotations.expose; import java.util.{list => javalist}  case class inbox(uuid:int,@expose(deserialize = false) messagelist:listbuffer[string]) {    val msglist:javalist[string] = messagelist    def tojson() = new gson().tojson(this)  }

i output

[info] running gsoninscala  object2json: {"uuid":4,"messagelist":{"scala$collection$mutable$listbuffer$$start":{},"last0":{"head":"orange","tl":{}},"exported":false,"len":3},"msglist":["apple","banana","orange"]} [success] total time: 2 s, completed 14-jul-2015 11:07:16

i hope helps you


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