Converting from scala.collection.immutable.List to a java.util.List in java

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英文:

Converting from scala.collection.immutable.List to a java.util.List in java

问题

I’m currently working within a java runtime google cloud dataflow. The scala sdk I'm using shows the property I'm working with as an immutable list: https://github.com/snowplow/snowplow-scala-analytics-sdk/blob/master/src/main/scala/com.snowplowanalytics.snowplow.analytics.scalasdk/Event.scala#L91

final List<SelfDescribingData> contexts

Does anyone have any pointers on how to properly cast / convert this to a Java list? Most of the examples I have found are doing this in the Scala runtime vs the Java runtime.

I had thought the JavaConverters package would help me here, however these methods don't seem to be expecting an immutable scala list.

Where e in the example below is an instance of the Event in the linked sdk.

List<SelfDescribingData> list = JavaConverters.asScalaBufferConverter(e.contexts()).asScala().toList();
for (SelfDescribingData t : list) {
LOG.info(t.toString());
}

英文:

I’m currently working within a java runtime google cloud dataflow. The scala sdk I'm using shows the property I'm working with as an immutable list: https://github.com/snowplow/snowplow-scala-analytics-sdk/blob/master/src/main/scala/com.snowplowanalytics.snowplow.analytics.scalasdk/Event.scala#L91

final List<SelfDescribingData<Json>> contexts

Does anyone have any pointers on how to properly cast / convert this to a Java list? Most of the examples I have found are doing this in the Scala runtime vs the Java runtime.

I had thought the JavaConverters package would help me here, however these methods don't seem to be expecting an immutable scala list.

Where e in the example below is an instance of the Event in the linked sdk.

List&lt;SelfDescribingData&lt;Json&gt;&gt; list = JavaConverters.asScalaBufferConverter(e.contexts()).asScala().toList();
for (SelfDescribingData&lt;Json&gt; t : list) {
    LOG.info(t.toString());
}

答案1

得分: 3

JavaConverters.asScalaBufferConverter

> 添加一个名为 asScala 的方法,隐式地将 Java List 转换为 Scala mutable Buffer

要将 scala.collection.immutable.List(它是 scala.collection.immutable.Seqscala.collection.Seq 的子类型)转换为 java.util.List,您可以调用 JavaConverters.asJava

java.util.List<SelfDescribingData<Json>> list = JavaConverters.asJava(e.contexts().data())

我发布的代码是在 Scala 2.13 集合重写之后的版本。对于较早版本的 Scala,等效函数是 JavaConverters.seqAsJavaList

英文:

JavaConverters.asScalaBufferConverter:

> Adds an asScala method that implicitly converts a Java List to a Scala mutable Buffer

To convert a scala.collection.immutable.List, which is a subtype of scala.collection.immutable.Seq and scala.collection.Seq to a java.util.List you would call JavaConverters.asJava:

java.util.List&lt;SelfDescribingData&lt;Json&gt;&gt; list = JavaConverters.asJava(e.contexts().data())

The code I've posted is after the Scala 2.13 collection rewrite. For older versions of Scala, the equivalent function is JavaConverters.seqAsJavaList

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  • 本文由 发表于 2020年8月5日 04:17:42
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