Scala

Question

我是Scala和SBT的新手。我正在找NullPointerException，请帮帮忙。

.profile

export LC_ALL=en_US.UTF-8
export LANG=en_US.UTF-8
export PYSPARK_PYTHON=/Library/Frameworks/Python.framework/Versions/3.5/bin/python3
export SPARK_HOME=/Softwares/spark
export R="/Library/Frameworks/R.framework/Resources"
export PATH=$PATH:$PYSPARK_PYTHON:$SPARK_HOME:$R

哪个scala

/usr/local/bin/scala

scala -version

cat: /release: No such file or directory
Scala code runner version 2.12.1 -- Copyright 2002-2016, LAMP/EPFL and Lightbend, Inc.

哪个sbt

/usr/local/bin/sbt

sbt关于这是sbt 0.13.13

我创建了一个包含以下内容的文件夹FirstScala/src/main/First/First.scala

object First
{
    def main(args:Array[String]) {
        println("First Scala Hello World");
    }
}

build.sbt

name := "first_scala"

version := "1.0"

scalaVersion := "2.12.1"

现在，在FirstScala文件夹中，我运行sbt包。生成.jar文件。但当我跑

scala target/scala-2.12/first_scala_2.12-1.0.jar 

我得到以下错误

java.lang.NullPointerException
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java:348)
at scala.reflect.internal.util.ScalaClassLoader.$anonfun$tryClass$1(ScalaClassLoader.scala:44)
at scala.util.control.Exception$Catch.$anonfun$opt$1(Exception.scala:242)
at scala.util.control.Exception$Catch.apply(Exception.scala:224)
at scala.util.control.Exception$Catch.opt(Exception.scala:242)
at scala.reflect.internal.util.ScalaClassLoader.tryClass(ScalaClassLoader.scala:44)
at scala.reflect.internal.util.ScalaClassLoader.tryToInitializeClass(ScalaClassLoader.scala:40)
at scala.reflect.internal.util.ScalaClassLoader.tryToInitializeClass$(ScalaClassLoader.scala:40)
at scala.reflect.internal.util.ScalaClassLoader$URLClassLoader.tryToInitializeClass(ScalaClassLoader.scala:129)
at scala.reflect.internal.util.ScalaClassLoader.run(ScalaClassLoader.scala:91)
at scala.reflect.internal.util.ScalaClassLoader.run$(ScalaClassLoader.scala:90)
at scala.reflect.internal.util.ScalaClassLoader$URLClassLoader.run(ScalaClassLoader.scala:129)
at scala.tools.nsc.CommonRunner.run(ObjectRunner.scala:22)
at scala.tools.nsc.CommonRunner.run$(ObjectRunner.scala:21)
at scala.tools.nsc.JarRunner$.run(MainGenericRunner.scala:13)
at scala.tools.nsc.CommonRunner.runAndCatch(ObjectRunner.scala:29)
at scala.tools.nsc.CommonRunner.runAndCatch$(ObjectRunner.scala:28)
at scala.tools.nsc.JarRunner$.runAndCatch(MainGenericRunner.scala:13)
at scala.tools.nsc.JarRunner$.runJar(MainGenericRunner.scala:25)
at scala.tools.nsc.MainGenericRunner.runTarget$1(MainGenericRunner.scala:65)
at scala.tools.nsc.MainGenericRunner.run$1(MainGenericRunner.scala:88)
at scala.tools.nsc.MainGenericRunner.process(MainGenericRunner.scala:99)
at scala.tools.nsc.MainGenericRunner$.main(MainGenericRunner.scala:104)
at scala.tools.nsc.MainGenericRunner.main(MainGenericRunner.scala)

提前谢谢。

Answer 1

1. 更改目录结构，使您拥有src/main/scala/First.scala，因为默认情况下，sbt需要此目录结构。
2. 您需要指定类路径和要运行的对象(First)的名称。
3. 使用sbt运行项目： 从/dev/ sbt /.sbt/0.13/ plugins信息中加载全局插件到first_scala (在构建文件中:/dev/FirstScala/)运行第一个Scala Hello成功总时间:0,2017年3月21日2:33:29 PM

参见在http://alvinalexander.com/scala/how-to-run-scala-sbt-packaged-jar-file-with-java-command上使用Java运行JAR的示例

您也可以使用Scala运行JAR，但是仍然需要指定类路径和对象名：http://alvinalexander.com/scala/how-to-run-scala-application-jar-files-set-classpath。

Answer 2

导出JAVA_HOME="$(/usr/libexec/java_home -v 1.8)“