How to fix NullpointerException error scala - scala

Question

So when i receive message from rabbitmq i want to send it to actor, but when i'm trying to match message i'm getting nullpointerexception. As it appears trouble occurs when i'm matching "msg" and trying send it to actor. Without this part " msg match {
case _ => drawer ! Drawer.Data(msg)
}" All works. How to fix it?
import java.util.UUID
import Client.{GameBullet, GameTank}
import akka.actor.{Actor, ActorLogging, ActorRef}
import com.rabbitmq.client.AMQP.BasicProperties
import com.rabbitmq.client.{AMQP, ConnectionFactory, DefaultConsumer, Envelope}
import org.json4s._
import org.json4s.jackson.JsonMethods._
import org.json4s.jackson.Serialization
import org.json4s.native.Serialization.{read, write}
object MessageSender {
case object Left
case object Right
case object Up
case object Down
case object StartGame
case object MakeShot
case object Start
}
case class Message(id:String,content:String)
class MessageSender(drawer:ActorRef) extends Actor with ActorLogging{
import MessageSender._
val factory = new ConnectionFactory()
factory.setHost("localhost")
val connection = factory.newConnection()
val channel = connection.createChannel()
val replyQueueName: String = channel.queueDeclare().getQueue
val corrId = UUID.randomUUID().toString
channel.queueBind(replyQueueName, "myDirect", replyQueueName)
val props = new BasicProperties.Builder().correlationId(corrId).replyTo(replyQueueName).build()
var currentId = 0
var message = ""
implicit val formats = Serialization.formats(ShortTypeHints(List(classOf[Message])))
override def receive: Receive = {
case StartGame =>
message="startGame"
var response: String = null
var msg:String =""
val code = pretty(render(Extraction.decompose(Message(currentId.toString,message))))
println(code)
channel.basicPublish("myDirect", "service", props, code.getBytes("UTF-8"))
println(replyQueueName)
println(corrId)
while(response == null){
val consumer = new DefaultConsumer(channel) {
override def handleDelivery(consumerTag: String,
envelope: Envelope,
properties: AMQP.BasicProperties,
body: Array[Byte]) {
msg = new String(body, "UTF-8")
println(properties.getCorrelationId)
println(s"message is $msg")
if(properties.getCorrelationId == corrId){
response = new String(body, "UTF-8")
}
}
}
channel.basicConsume(replyQueueName, true, consumer)
}
currentId=response.toInt
log.info(s"Session started [$currentId]")
msg match {
case _ => drawer ! Drawer.Data(msg)
}
self ! Start
}
}
Error:
This i get when i try match msg

Answer 1

According to the attached screenshot, the exception occurs on line 83 of this class.
The problem is therefore that the drawer member is null, so drawer ! Drawer.Data(msg) throws NPE.
I would guess that the initialization of the actor (using props) is done with a variable that is defined later in the same scope resulting with a "froward reference".
See my example in your other related question (Scala Akka NullPointerException error)