在Scala中使用包？

我有一个使用akka的scala项目。我希望执行上下文在整个项目中都可用。我创建了一个包对象，如下所示：

import akka.actor.ActorSystem
import akka.stream.ActorMaterializer
import com.datastax.driver.core.Cluster

package object connector {

  implicit val system = ActorSystem()
  implicit val mat = ActorMaterializer()

  implicit val executionContext = executionContext

    implicit val session = Cluster
    .builder
      .addContactPoints("localhost")
      .withPort(9042)
      .build()
      .connect()


}

在同一个包中，我有以下文件：

import akka.stream.alpakka.cassandra.scaladsl.CassandraSource
import akka.stream.scaladsl.Sink
import com.datastax.driver.core.{Row, Session, SimpleStatement}

import scala.collection.immutable
import scala.concurrent.Future

object CassandraService {

    def selectFromCassandra()() = {

      val statement = new SimpleStatement(s"SELECT * FROM animals.alpakka").setFetchSize(20)
      val rows: Future[immutable.Seq[Row]] = CassandraSource(statement).runWith(Sink.seq)

      rows.map{item =>
       print(item)

      }
    }
}

---

然而，我得到的编译器错误，没有执行上下文或会话可以找到。我对package关键字的理解是，该对象中的所有内容都将在整个包中可用。但这似乎不起作用。如果能向我解释一下，我将不胜感激

您的实现必须是这样的，希望能有所帮助

package.scala

package com.app.akka

package object connector {
  // Do some codes here..
}

package com.app.akka
import com.app.akka.connector._

object CassandraService {
  def selectFromCassandra() = {
    // Do some codes here..
  }
}

CassandraService.scala

package com.app.akka

package object connector {
  // Do some codes here..
}

package com.app.akka
import com.app.akka.connector._

object CassandraService {
  def selectFromCassandra() = {
    // Do some codes here..
  }
}

---

您的实现必须是这样的，希望它能有所帮助

package.scala

package com.app.akka

package object connector {
  // Do some codes here..
}

package com.app.akka
import com.app.akka.connector._

object CassandraService {
  def selectFromCassandra() = {
    // Do some codes here..
  }
}

CassandraService.scala

package com.app.akka

package object connector {
  // Do some codes here..
}

package com.app.akka
import com.app.akka.connector._

object CassandraService {
  def selectFromCassandra() = {
    // Do some codes here..
  }
}

---

您当前的代码有两个问题

编译包对象连接器时，会抛出以下错误

错误：（14，35）递归值executionContext需要类型 隐式val executionContext=executionContext 问题在于隐式val executionContext=executionContext行 此问题的解决方案如下所示

隐式val executionContext=executionContext

当我们编译CassandraService时，它会抛出如下错误

错误：（17，13）找不到隐式ExecutionContext。你可以通过 方法的（隐式ec:ExecutionContext）参数 或导入scala.concurrent.ExecutionContext.Implicits.global。 rows.map{item=>

错误明确指出，要么我们需要将ExecutionContext作为隐式参数传递，要么导入scala.concurrent.ExecutionContext.Implicits.global。在我的系统中，这两个问题都得到了解决，并且编译成功。我附上了代码供您参考

package com.apache.scala

import akka.actor.ActorSystem
import akka.stream.ActorMaterializer
import com.datastax.driver.core.Cluster
import scala.concurrent.ExecutionContext


package object connector {

  implicit val system = ActorSystem()
  implicit val mat = ActorMaterializer()

  implicit val executionContext = ExecutionContext

  implicit val session = Cluster
    .builder
    .addContactPoints("localhost")
    .withPort(9042)
    .build()
    .connect()

}

package com.apache.scala.connector

import akka.stream.alpakka.cassandra.scaladsl.CassandraSource
import akka.stream.scaladsl.Sink
import com.datastax.driver.core.{Row, SimpleStatement}

import scala.collection.immutable
import scala.concurrent.ExecutionContext.Implicits.global
import scala.concurrent.Future

object CassandraService {

  def selectFromCassandra() = {

    val statement = new SimpleStatement(s"SELECT * FROM animals.alpakka").setFetchSize(20)
    val rows: Future[immutable.Seq[Row]] = CassandraSource(statement).runWith(Sink.seq)

    rows.map{item =>
      print(item)

    }
  }

}

---

您当前的代码有两个问题

编译包对象连接器时，会抛出以下错误

错误：（14，35）递归值executionContext需要类型 隐式val executionContext=executionContext 问题在于隐式val executionContext=executionContext行 此问题的解决方案如下所示

隐式val executionContext=executionContext

当我们编译CassandraService时，它会抛出如下错误

错误：（17，13）找不到隐式ExecutionContext。您可能会通过 方法的（隐式ec:ExecutionContext）参数 或导入scala.concurrent.ExecutionContext.Implicits.global。 rows.map{item=>

错误明确指出，要么我们需要将ExecutionContext作为隐式参数传递，要么导入scala.concurrent.ExecutionContext.Implicits.global。在我的系统中，这两个问题都得到了解决，并且编译成功。我附上了代码供您参考

package com.apache.scala

import akka.actor.ActorSystem
import akka.stream.ActorMaterializer
import com.datastax.driver.core.Cluster
import scala.concurrent.ExecutionContext


package object connector {

  implicit val system = ActorSystem()
  implicit val mat = ActorMaterializer()

  implicit val executionContext = ExecutionContext

  implicit val session = Cluster
    .builder
    .addContactPoints("localhost")
    .withPort(9042)
    .build()
    .connect()

}

package com.apache.scala.connector

import akka.stream.alpakka.cassandra.scaladsl.CassandraSource
import akka.stream.scaladsl.Sink
import com.datastax.driver.core.{Row, SimpleStatement}

import scala.collection.immutable
import scala.concurrent.ExecutionContext.Implicits.global
import scala.concurrent.Future

object CassandraService {

  def selectFromCassandra() = {

    val statement = new SimpleStatement(s"SELECT * FROM animals.alpakka").setFetchSize(20)
    val rows: Future[immutable.Seq[Row]] = CassandraSource(statement).runWith(Sink.seq)

    rows.map{item =>
      print(item)

    }
  }

}

---

您的文件是否包含

包

声明？您的文件是否包含

包

声明？