RE: Partition Key Cannot be Send Out by Producer

[Haoming Zhang]

Hi Harsha,

I just tried to hard code a string message, then convert the message to byte 
array, but no lucky...

The following is how my program works:

Create a hardcode key, which is String, then convert to byte array, iterate a 
network message, send the message one by one:
      networkelements foreach {
        case networkelement =>
          val bytes = Injection(networkelement)
          logger.info(s"Synchronously sending Tweet $networkelement to topic 
${producerApp.defaultTopic}")

          val hardKey = "2"
          val parkey = hardKey.getBytes("UTF8")
          val topic = producerApp.defaultTopic
          producerApp.send(parkey, bytes, topic)
      }


Here is how the networkelements created, where NetworkElement is a class that 
created by avro, I think you can ignore it:
val networkelements = fixture.messages

  val fixture = {
    val BeginningOfEpoch = 0.seconds
    val AnyTimestamp = 1234.seconds
    val now = System.currentTimeMillis().millis

    new {
      val t1 = new NetworkElement("ANY_USER_1", "ANY_TEXT_1", now.toSeconds)
      val t2 = new NetworkElement("ANY_USER_2", "ANY_TEXT_2", 
BeginningOfEpoch.toSeconds)
      val t3 = new NetworkElement("ANY_USER_3", "ANY_TEXT_3", 
AnyTimestamp.toSeconds)

      val messages = Seq(t1, t2, t3)
    }
  }

BTW, I defined the Key and Val types as following:

  type Key = Array[Byte]
  type Val = Array[Byte]

Thanks,
Haoming

> From: ka...@harsha.io
> To: users@kafka.apache.org
> Subject: Re: Partition Key Cannot be Send Out by Producer
> Date: Thu, 20 Nov 2014 16:59:19 -0800
> 
> also the (key: Key, value: Val, topic: Option[String]) "value" should be
> a string converted to a byte array.
> Can you send a example of your key and value data.
> 
> 
> On Thu, Nov 20, 2014, at 04:53 PM, Haoming Zhang wrote:
> > Hi Harsha,
> > 
> > Thanks for suggestion!
> > 
> > I have checked this link before, and I tried to create the partition key
> > like the following:
> >           val hardKey = "2"
> >           val parkey = hardKey.getBytes("UTF8")
> > 
> > But I still get the same exception. I also tried set "UTF8" as "UTF-8",
> > but no luck...
> > 
> > Regards,
> > Haoming
> > 
> > > From: ka...@harsha.io
> > > To: users@kafka.apache.org
> > > Subject: Re: Partition Key Cannot be Send Out by Producer
> > > Date: Thu, 20 Nov 2014 16:43:11 -0800
> > > 
> > > Hi Haoming,
> > >           Take a look at the code here
> > >           
> > > https://github.com/stealthly/scala-kafka/blob/master/src/main/scala/KafkaProducer.scala
> > > for your partKey it should be string and when you converting it into
> > > byte array you can use partKey.getBytes("UTF8")
> > > -Harsha
> > > 
> > > On Thu, Nov 20, 2014, at 03:57 PM, Haoming Zhang wrote:
> > > > Hi all,
> > > > 
> > > > I'm a beginner of Kafka, currently I'm stuck by how to send out a
> > > > KeyedMessage by producer. I would like to design a partition
> > > > function to route the message based on the key, but the producer cannot
> > > > send the KeyedMessage and I got this exception:
> > > > java.lang.ClassCastException: [B cannot be cast to java.lang.String
> > > > 
> > > > What I tried is hardcode a partition key ( I tried String and Integer,
> > > > currently it is Integer ), then convert the partition key to Byte Array:
> > > >           val converter = new DataTypeConvertion
> > > >           val hardKey = 2
> > > >           val partkey = converter.intToByteArray(hardKey)
> > > > 
> > > >  Then create a KeyedMessage by the following function:
> > > > 
> > > >   private def toMessage(value: Val, key: Option[Key] = None, topic:
> > > >   Option[String] = None): KeyedMessage[Key, Val] = {
> > > >     val t = topic.get
> > > >     require(!t.isEmpty, "Topic must not be empty")
> > > >     key match {
> > > >       case Some(key) => new KeyedMessage(t, key, value)
> > > >       case _ => new KeyedMessage(t, value)
> > > >     }
> > > >   }
> > > > 
> > > > Then try to send the KeyedMessage by a Kafka producer:
> > > > 
> > > >   def send(key: Key, value: Val, topic: Option[String] = None) {
> > > >     val msg = toMessage(value, Option(key), topic)
> > > >     print(msg + "\n")
> > > >     print("msg.key" + msg.key + "\n")
> > > >     print("msg.message" + msg.message + "\n")
> > > >     print("msg.partKey" + msg.partKey + "\n")
> > > >     print("msg.topic" + msg.topic + "\n")
> > > >     try {
> > > >       p.send(msg) //P is an instance of producer, exception happens in
> > > >       this line
> > > >     } catch {
> > > >       case e: Exception =>
> > > >         e.printStackTrace()
> > > >         System.exit(1)
> > > >     }
> > > >   }
> > > > 
> > > > As you can see, I added many print statement in the above function, and
> > > > the following is the output of above function:
> > > > KeyedMessage(testingInput,[B@7ad40950,[B@7ad40950,[B@7ce18764)
> > > > msg.key: [B@7ad40950
> > > > msg.message: [B@7ce18764
> > > > msg.partKey: [B@7ad40950
> > > > msg.topic: testingInput
> > > > 
> > > > The key of KeyedMessage is displayed as [B@7ad40950 , I think it is a
> > > > memory address and the exception (java.lang.ClassCastException: [B 
> > > > cannot
> > > > be cast to java.lang.String) happens when "send" function try to convert
> > > > the Byte Array to String.
> > > > 
> > > > Am I wrong on creating a key in Byte Array type?
> > > > Some examples of how to use KeyedMessage will be great!
> > > > 
> > > > Regards,
> > > > Haoming
> > > > 
> > > >                                           
> >