Scala - Tips

1- 运行scala命令，提示报错

问题现象：

在Windows7系统中安装scala后(直接安装MSI包，或者解压zip包添加环境变量的方式)，执行scala命令报错，但可以执行scala -version

Microsoft Windows [Version 6.1.7601]
Copyright (c) 2009 Microsoft Corporation.  All rights reserved.

C:\Users\guowli>scala
Welcome to Scala 2.12.4 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_101).
Type in expressions for evaluation. Or try :help.

scala> java.lang.NullPointerException
        at java.util.Arrays.sort(Arrays.java:1438)
        at scala.tools.nsc.classpath.JFileDirectoryLookup.listChildren(DirectoryClassPath.scala:113)
        at scala.tools.nsc.classpath.JFileDirectoryLookup.listChildren$(DirectoryClassPath.scala:97)
        at scala.tools.nsc.classpath.DirectoryClassPath.listChildren(DirectoryClassPath.scala:202)
        at scala.tools.nsc.classpath.DirectoryClassPath.listChildren(DirectoryClassPath.scala:202)
        at scala.tools.nsc.classpath.DirectoryLookup.list(DirectoryClassPath.scala:73)
        at scala.tools.nsc.classpath.DirectoryLookup.list$(DirectoryClassPath.scala:69)
        at scala.tools.nsc.classpath.DirectoryClassPath.list(DirectoryClassPath.scala:202)
        at scala.tools.nsc.classpath.AggregateClassPath.$anonfun$list$1(AggregateClassPath.scala:76)
        at scala.collection.TraversableLike.$anonfun$map$1(TraversableLike.scala:234)
        at scala.collection.Iterator.foreach(Iterator.scala:929)
        at scala.collection.Iterator.foreach$(Iterator.scala:929)
        at scala.collection.AbstractIterator.foreach(Iterator.scala:1417)
        at scala.collection.IterableLike.foreach(IterableLike.scala:71)
        at scala.collection.IterableLike.foreach$(IterableLike.scala:70)
        at scala.collection.AbstractIterable.foreach(Iterable.scala:54)
        at scala.collection.TraversableLike.map(TraversableLike.scala:234)
        at scala.collection.TraversableLike.map$(TraversableLike.scala:227)
        at scala.collection.AbstractTraversable.map(Traversable.scala:104)
        at scala.tools.nsc.classpath.AggregateClassPath.list(AggregateClassPath.scala:74)
        at scala.tools.nsc.symtab.SymbolLoaders$PackageLoader.doComplete(SymbolLoaders.scala:271)
        at scala.tools.nsc.symtab.SymbolLoaders$SymbolLoader.complete(SymbolLoaders.scala:220)
        at scala.reflect.internal.Symbols$Symbol.info(Symbols.scala:1530)
        at scala.reflect.internal.Mirrors$RootsBase.init(Mirrors.scala:225)
        at scala.tools.nsc.Global.rootMirror$lzycompute(Global.scala:65)
        at scala.tools.nsc.Global.rootMirror(Global.scala:63)
        at scala.tools.nsc.Global.rootMirror(Global.scala:36)
        at scala.reflect.internal.Definitions$DefinitionsClass.ObjectClass$lzycompute(Definitions.scala:267)
        at scala.reflect.internal.Definitions$DefinitionsClass.ObjectClass(Definitions.scala:267)
        at scala.reflect.internal.Definitions$DefinitionsClass.init(Definitions.scala:1422)
        at scala.tools.nsc.Global$Run.<init>(Global.scala:1164)
        at scala.tools.nsc.interpreter.IMain._initialize(IMain.scala:125)
        at scala.tools.nsc.interpreter.IMain.initializeSynchronous(IMain.scala:147)
        at scala.tools.nsc.interpreter.ILoop.$anonfun$process$11(ILoop.scala:1030)
        at scala.tools.nsc.interpreter.ILoop.startup$1(ILoop.scala:1011)
        at scala.tools.nsc.interpreter.ILoop.process(ILoop.scala:1049)
        at scala.tools.nsc.MainGenericRunner.runTarget$1(MainGenericRunner.scala:82)
        at scala.tools.nsc.MainGenericRunner.run$1(MainGenericRunner.scala:85)
        at scala.tools.nsc.MainGenericRunner.process(MainGenericRunner.scala:96)
        at scala.tools.nsc.MainGenericRunner$.main(MainGenericRunner.scala:101)
        at scala.tools.nsc.MainGenericRunner.main(MainGenericRunner.scala)

C:\Users\guowli>

C:\Users\guowli>scala -version
Scala code runner version 2.12.4 -- Copyright 2002-2017, LAMP/EPFL and Lightbend, Inc.

C:\Users\guowli>

原因分析：

可以执行scala -version命令，说明scala的环境变量是正确的。

无法scala命令，可能是调用相关库失败，检查Java是否正确安装和Scala环境变量Classpath的配置

处理方法：

1- 检查java和javac的版本是否可用并一致

2- 检查环境变量

设置 Classpath 变量（也可能为CLASSPATH，不区分大小写）：找到找到系统变量下的"Classpath"，单击编辑，添加如下内容

;%SCALA_HOME%\bin;%SCALA_HOME%\lib\dt.jar;%SCALA_HOME%\lib\tools.jar.;

注意："变量值"最前面的 .; 不要漏掉。最后单击确定即可。

2- 在Win7 64bit系统cmd命令行下运行sbt命令，提示报错

在Windows7 64bit系统中安装sbt（未重启系统）后，在cmd命令行下执行sbt命令报错

Microsoft Windows [Version 6.1.7601]
Copyright (c) 2009 Microsoft Corporation.  All rights reserved.

C:\Users\guowli>sbt
"C:\Users\guowli\.sbt\preloaded\org.scala-sbt\sbt\"1.0.2"\jars\sbt.jar"
Java HotSpot(TM) 64-Bit Server VM warning: ignoring option MaxPermSize=256m; support was removed in 8.0
Getting org.fusesource.jansi jansi 1.11 ...

:: problems summary ::
:::: WARNINGS
                module not found: org.fusesource.jansi#jansi;1.11

        ==== local: tried

          C:\Users\guowli\.ivy2\local\org.fusesource.jansi\jansi\1.11\ivys\ivy.xml

          -- artifact org.fusesource.jansi#jansi;1.11!jansi.jar:

          C:\Users\guowli\.ivy2\local\org.fusesource.jansi\jansi\1.11\jars\jansi.jar

        ==== local-preloaded-ivy: tried

          file:/C:/Users/guowli/.sbt/preloaded/org.fusesource.jansi/jansi/1.11/ivys/ivy.xml

        ==== local-preloaded: tried

          file:/C:/Users/guowli/.sbt/preloaded/org/fusesource/jansi/jansi/1.11/jansi-1.11.pom

          -- artifact org.fusesource.jansi#jansi;1.11!jansi.jar:

          file:/C:/Users/guowli/.sbt/preloaded/org/fusesource/jansi/jansi/1.11/jansi-1.11.jar

        ==== Maven Central: tried

          https://repo1.maven.org/maven2/org/fusesource/jansi/jansi/1.11/jansi-1.11.pom

          -- artifact org.fusesource.jansi#jansi;1.11!jansi.jar:

          https://repo1.maven.org/maven2/org/fusesource/jansi/jansi/1.11/jansi-1.11.jar

        ==== sbt-maven-releases: tried

          https://repo.scala-sbt.org/scalasbt/maven-releases/org/fusesource/jansi/jansi/1.11/jansi-1.11.pom

          -- artifact org.fusesource.jansi#jansi;1.11!jansi.jar:

          https://repo.scala-sbt.org/scalasbt/maven-releases/org/fusesource/jansi/jansi/1.11/jansi-1.11.jar

        ==== sbt-maven-snapshots: tried

          https://repo.scala-sbt.org/scalasbt/maven-snapshots/org/fusesource/jansi/jansi/1.11/jansi-1.11.pom

          -- artifact org.fusesource.jansi#jansi;1.11!jansi.jar:

          https://repo.scala-sbt.org/scalasbt/maven-snapshots/org/fusesource/jansi/jansi/1.11/jansi-1.11.jar

        ==== typesafe-ivy-releases: tried

          https://repo.typesafe.com/typesafe/ivy-releases/org.fusesource.jansi/jansi/1.11/ivys/ivy.xml

        ==== sbt-ivy-snapshots: tried

          https://repo.scala-sbt.org/scalasbt/ivy-snapshots/org.fusesource.jansi/jansi/1.11/ivys/ivy.xml

                ::::::::::::::::::::::::::::::::::::::::::::::

                ::          UNRESOLVED DEPENDENCIES         ::

                ::::::::::::::::::::::::::::::::::::::::::::::

                :: org.fusesource.jansi#jansi;1.11: not found

                ::::::::::::::::::::::::::::::::::::::::::::::

:::: ERRORS
        Server access Error: Connection timed out: connect url=https://repo1.maven.org/maven2/org/fusesource/jansi/jansi
/1.11/jansi-1.11.pom

        Server access Error: Connection timed out: connect url=https://repo1.maven.org/maven2/org/fusesource/jansi/jansi
/1.11/jansi-1.11.jar

        Server access Error: Connection timed out: connect url=https://repo.scala-sbt.org/scalasbt/maven-releases/org/fu
sesource/jansi/jansi/1.11/jansi-1.11.pom

        Server access Error: Connection timed out: connect url=https://repo.scala-sbt.org/scalasbt/maven-releases/org/fu
sesource/jansi/jansi/1.11/jansi-1.11.jar

        Server access Error: Connection timed out: connect url=https://repo.scala-sbt.org/scalasbt/maven-snapshots/org/f
usesource/jansi/jansi/1.11/jansi-1.11.pom

        Server access Error: Connection timed out: connect url=https://repo.scala-sbt.org/scalasbt/maven-snapshots/org/f
usesource/jansi/jansi/1.11/jansi-1.11.jar

        Server access Error: Connection timed out: connect url=https://repo.typesafe.com/typesafe/ivy-releases/org.fuses
ource.jansi/jansi/1.11/ivys/ivy.xml

        Server access Error: Connection timed out: connect url=https://repo.scala-sbt.org/scalasbt/ivy-snapshots/org.fus
esource.jansi/jansi/1.11/ivys/ivy.xml

:: USE VERBOSE OR DEBUG MESSAGE LEVEL FOR MORE DETAILS
unresolved dependency: org.fusesource.jansi#jansi;1.11: not found
Error during sbt execution: Error retrieving required libraries
  (see C:\Users\guowli\.sbt\boot\update.log for complete log)
Error: Could not retrieve jansi 1.11

C:\Users\guowli>

原因分析：

网络原因的导致无法获得依赖包

处理方法：

http://www.scala-sbt.org/0.13/docs/Proxy-Repositories.html

• 设置可用的repo或代理。
• 在用户目录下创建.sbt目录，放一个repositories文件
• 在用户的~/.sbt目录和安装目录，例如：“C:\Program Files (x86)\sbt\conf”

guowli@5CG450158J MINGW64 ~/.sbt
$ ll
total 17
drwxr-xr-x 1 guowli 1049089   0 Nov  2 11:29 1.0/
drwxr-xr-x 1 guowli 1049089   0 Nov  2 13:38 boot/
drwxr-xr-x 1 guowli 1049089   0 Oct 26 10:55 preloaded/
-rw-r--r-- 1 guowli 1049089 880 Nov  2 13:29 repositories
-rw-r--r-- 1 guowli 1049089 253 Nov  2 13:30 sbtconfig.txt

guowli@5CG450158J MINGW64 ~/.sbt
$ cat repositories
[repositories]
    local
    maven-repo2-ivy-releases: http://repo2.maven.org/maven2/, , [organization]/[module]/(scala_[scalaVersion]/)(sbt_[sbtVersion]/)[revision]/[type]s/[artifact](-[classifier]).[ext]
    maven-repo2: http://repo2.maven.org/maven2/
    maven-central-ivy-releases: http://repo1.maven.org/maven2/, , [organization]/[module]/(scala_[scalaVersion]/)(sbt_[sbtVersion]/)[revision]/[type]s/[artifact](-[classifier]).[ext]
    maven-central: http://repo1.maven.org/maven2/
    sbt-releases-repo: http://repo.typesafe.com/typesafe/ivy-releases/, , [organization]/[module]/(scala_[scalaVersion]/)(sbt_[sbtVersion]/)[revision]/[type]s/[artifact](-[classifier]).[ext]
    sbt-plugins-repo: http://repo.scala-sbt.org/scalasbt/sbt-plugin-releases/, , [organization]/[module]/(scala_[scalaVersion]/)(sbt_[sbtVersion]/)[revision]/[type]s/[artifact](-[classifier]).[ext]
guowli@5CG450158J MINGW64 ~/.sbt
$

guowli@5CG450158J MINGW64 ~/.sbt
$ cat sbtconfig.txt
# Set the java args to high

-Xmx512M

-XX:MaxPermSize=256m

-XX:ReservedCodeCacheSize=128m

# Set the extra SBT options

-Dsbt.log.format=true

-Dhttp.proxySet=true

-Dhttp.proxyHost=10.144.1.10

-Dhttp.proxyPort=8080

-Dsbt.override.build.repos=true
guowli@5CG450158J MINGW64 ~/.sbt
$

参考信息：

• https://my.oschina.net/u/915967/blog/146746
• https://stackoverflow.com/questions/27540058/installing-sbt-on-win-7-64-bit
• https://stackoverflow.com/questions/29140202/typesafe-activator-running-error-could-not-retrieve-jansi-1-11

3- 在REPL命令行下，编辑大块代码

示例： 利用“:paste”选项

Microsoft Windows [Version 6.1.7601]
Copyright (c) 2009 Microsoft Corporation.  All rights reserved.

C:\Users\guowli>scala
Welcome to Scala 2.12.4 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_101).
Type in expressions for evaluation. Or try :help.

scala> :paste
// Entering paste mode (ctrl-D to finish)

  def qSort(x: List[Int]): List[Int] = {
    if (x.length <= 2) x
    else qSort(x.filter(x.head > _)) ++
      x.filter(x.head == _) ++
      qSort(x.filter(x.head < _))
  }

// Exiting paste mode, now interpreting.

qSort: (x: List[Int])List[Int]

scala> qSort(List(6, 4, 5, 3, 1, 2, 9, 8, 0, 7))
res0: List[Int] = List(0, 1, 2, 3, 4, 5, 6, 8, 7, 9)

scala>

4- main方法

对于一个Scala应用程序而言，必须包含main方法。

如果没有包含main方法，就不能使用scalac命令进行编译，而是直接使用scala命令运行代码。