Scala "constructor DCAwareRoundRobinPolicy in class DCAwareRoundRobinPolicy cannot be accessed in object CassandraConnector"

Question

I am a scala newbie and really need help with an issue I've been experiencing with some code. I have set up the following code to create cassandra connections:

package some.package

import java.net.InetAddress
import java.util

import com.datastax.driver.core._
import com.datastax.driver.core.policies.{DCAwareRoundRobinPolicy, TokenAwarePolicy}

import scala.collection.JavaConversions._

object CassandraConnector {

  def getCluster(contactPointIpString: String, preferred_dc: String): Cluster = {

    val contactPointIpStrings = contactPointIpString.split(",").toList

    val contactPointIpList = contactPointIpStrings.flatMap { ipAddress: String => InetAddress.getAllByName(ipAddress) }
    println(s"Building Cluster w/ Contact Points: $contactPointIpList")

    Cluster.builder()
      .addContactPoints(contactPointIpList)
      .withClusterName("multi_dc_user_data")
      .withLoadBalancingPolicy(new TokenAwarePolicy(new DCAwareRoundRobinPolicy(preferred_dc)))
      .withQueryOptions(new QueryOptions().setConsistencyLevel(ConsistencyLevel.LOCAL_ONE))
      .build()
  }

}

While building the project in IntelliJ, the following error happens:

constructor DCAwareRoundRobinPolicy in class DCAwareRoundRobinPolicy cannot be accessed in object CassandraConnector
      .withLoadBalancingPolicy(new TokenAwarePolicy(new DCAwareRoundRobinPolicy(preferred_dc)))

Found something similar to my problem here, and tried to change my code to the following:

val dcAwareRoundRobinPolicyBuilder = new DCAwareRoundRobinPolicy.Builder
val dcAwareRoundRobinPolicy = dcAwareRoundRobinPolicyBuilder.withLocalDc(preferred_dc)

Cluster.builder()
  .addContactPoints(contactPointIpList)
  .withClusterName("multi_dc_user_data")
  .withLoadBalancingPolicy(new TokenAwarePolicy(dcAwareRoundRobinPolicy.build()))
  .withQueryOptions(new QueryOptions().setConsistencyLevel(ConsistencyLevel.LOCAL_ONE))
  .build()

This resolved the issue and now the build finishes successfully but I am not so sure if what I've done is necessarily correct, so I'd really appreciate any help in this regard.

score 0 · Answer 1 · answered Aug 20 '20 at 03:41

DCAwareRoundRobinPolicy uses the Builder Pattern to decouple the public API for instance creation from the particular implementation of the constructors for the instances. This is accomplished by not exposing a public constructor and instead only allowing DCAwareRoundRobinPolicy.Builder to construct instances of DCAwareRoundRobinPolicy.

You're using it as it's intended (assuming that you're passing options which match what you're expecting).

Scala "constructor DCAwareRoundRobinPolicy in class DCAwareRoundRobinPolicy cannot be accessed in object CassandraConnector"

1 Answers1