最近新入职公司，所在项目组使用hadoop较多，基本都在使用spark做计算，为了更好的操作spark最近也在学习scala这门语言（原因：spark源码是scala）。

新遇问题：众所周知，java 和scala是可以相互调用的，在调用的时候，集合类的相互转化会有问题。也就是说，java的List和scala的List是不一样的，解决后以此记录。

以下为官方可直接转换列表(单向 =>, 双向<=>)：

scala.collection.Iterable <=> .java.lang.Iterable

scala.collection.Iterable <=> java.util.Collection

scala.collection.Iterator <=> java.util.{ Iterator, Enumeration }

scala.collection.mutable.Buffer <=> java.util.List

scala.collection.mutable.Set <=> java.util.Set

scala.collection.mutable.Map <=> java.util.{ Map, Dictionary }

scala.collection.mutable.ConcurrentMap <=> java.util.concurrent.ConcurrentMap

scala.collection.Seq         => java.util.List

scala.collection.mutable.Seq => java.util.List

scala.collection.Set         => java.util.Set

scala.collection.Map         => java.util.Map

java.util.Properties         => scala.collection.mutable.Map[String, String]

转换的关键在于:   scala.collection.JavaConverters   这个工具类包含了基本的转换情景

话不多说上代码:

· Scala代码:

/**
 * Map 互相转换
 **/
def convert2JavaMap(scalaMap: Map[String, String]): Unit = {
  //scala Map ==> java Map
  val javaMap: util.Map[String, String] = scalaMap.asJava
  //java Map ==> scala Map
  import scala.collection.JavaConversions.mapAsScalaMap
  val scalaMap1: scala.collection.mutable.Map[String, String] = javaMap
}

/**
  * List 互相转换
  **/
def convert2JavaList(scalaList: List[String]): Unit = {
  //java List ==> scala List
  val javaList: java.util.List[String] = scalaList.asJava
  //scala List ==> java List
  val buffer: scala.collection.mutable.Buffer[String] = javaList.asScala
  val list: List[String] = buffer.toList
}

/** 
  * 略微复杂的结构
  **/
def convert2JavaMaps(scalaMapList: List[Map[String, String]]): java.util.List[java.util.Map[String, String]] = {
  val arrayBuffer = ArrayBuffer[util.Map[String, String]]()
  val javaList: util.List[Map[String, String]] = scalaMapList.asJava
  for (i <- 0 until javaList.size()) {
    val javaMap: util.Map[String, String] = javaList.get(i).asJava
    arrayBuffer += javaMap
  }
  val javaMapList: util.List[util.Map[String, String]] = arrayBuffer.toArray.toList.asJava
  javaMapList
}

· Java代码:

/**
 * List 互相转换
 **/
public static void convert2List(scala.collection.immutable.List<String> scalaList){
    //scala List ==> java List
    List<String> javaList = JavaConversions.seqAsJavaList(scalaList);
    //java List ==> scala List
    scalaList = JavaConversions.asScalaIterator(javaList.iterator()).toSeq().toList();
}
/**
  * Map 互相转换
 **/
public static void convert2Map(scala.collection.Map<String, String> scalaMap){
    //scala Map ==> java Map
    Map<String, String> javaMap = JavaConversions.mapAsJavaMap(scalaMap);
    //java List ==> scala List
    scalaMap= JavaConversions.mapAsScalaMap(javaMap);
}

如何选择这几种方法，取决于在哪边抽象成工具，统一处理。

初学者总结，如有不当请指教。