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
>
>
