samza-core/src/main/scala/org/apache/samza/util/ScalaJavaUtil.scala

/*
 *
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 *
 */

package org.apache.samza.util

import java.util
import java.util.{Optional, function}

import scala.collection.JavaConverters
import scala.collection.immutable.Map
import scala.collection.JavaConverters._
import scala.runtime.AbstractFunction0

object ScalaJavaUtil {

  /**
    * Convert a Java map to a Scala immutable Map
    * */
  def toScalaMap[K, V](javaMap: java.util.Map[K, V]): Map[K, V] = {
    javaMap.asScala.toMap
  }

  /**
    * Convert a scala iterable to a Java collection.
    */
  def toJavaCollection[T](iterable : Iterable[T]): util.Collection[T] = {
    JavaConverters.asJavaCollectionConverter(iterable).asJavaCollection
  }

  /**
    * Wraps the provided value in an Scala Function, e.g. for use in [[Option#getOrDefault]]
    *
    * @param value the value to be wrapped
    * @tparam T type of the value
    * @return an AbstractFunction0 that returns contained value when called
    */
  def defaultValue[T](value: T): AbstractFunction0[T] = {
    new AbstractFunction0[T] {
      override def apply(): T = value
    }
  }

  def toJavaFunction[T, R](scalaFunction: Function1[T, R]): java.util.function.Function[T, R] = {
    new function.Function[T, R] {
      override def apply(t: T): R = scalaFunction.apply(t)
    }
  }

  /**
    * Wraps the provided Java Supplier in an Scala Function, e.g. for use in [[Option#getOrDefault]]
    *
    * @param javaFunction the java Supplier function to be wrapped
    * @tparam T type of the value
    * @return an AbstractFunction0 that returns contained value when called
    */
  def toScalaFunction[T](javaFunction: java.util.function.Supplier[T]): AbstractFunction0[T] = {
    new AbstractFunction0[T] {
      override def apply(): T = javaFunction.get()
    }
  }

  def toScalaFunction[T, R](javaFunction: java.util.function.Function[T, R]): Function1[T, R] = {
    t => javaFunction.apply(t)
  }


  /**
    * Conversions between Scala Option and Java 8 Optional.
    */
  object JavaOptionals {
    implicit def toRichOption[T](opt: Option[T]): RichOption[T] = new RichOption[T](opt)
    implicit def toRichOptional[T](optional: Optional[T]): RichOptional[T] = new RichOptional[T](optional)
  }

  class RichOption[T] (opt: Option[T]) {

    /**
      * Transform this Option to an equivalent Java Optional
      */
    def toOptional: Optional[T] = Optional.ofNullable(opt.getOrElse(null).asInstanceOf[T])
  }

  class RichOptional[T] (opt: Optional[T]) {

    /**
      * Transform this Optional to an equivalent Scala Option
      */
    def toOption: Option[T] = if (opt.isPresent) Some(opt.get()) else None
  }

}