即将在具有依赖项的scala项目中加载一个主类

Question

我试图在scala中使用一个主对象，但SBT返回以下消息：

> package
[info] Packaging /Users/aironman/scala_cassandra_project_without_play/target/scala-2.10/my-project_2.10-0.1-SNAPSHOT.jar ...
[info] Done packaging.
[info] Packaging /Users/aironman/scala_cassandra_project_without_play/common/target/scala-2.11/common_2.11-0.1.jar ...
[info] Done packaging.
[info] Packaging /Users/aironman/scala_cassandra_project_without_play/main/target/scala-2.11/main_2.11-0.1.jar ...
[info] Done packaging.
[success] Total time: 0 s, completed 11-mar-2016 11:25:16
> run
[info] Running common.utils.cassandra.CassandraMain 
[error] (run-main-1) java.lang.ClassNotFoundException: common.utils.cassandra.CassandraMain
java.lang.ClassNotFoundException: common.utils.cassandra.CassandraMain
at java.lang.ClassLoader.findClass(ClassLoader.java:530)
at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
[trace] Stack trace suppressed: run last scala_cassandra_project_without_play/compile:run for the full output.
java.lang.RuntimeException: Nonzero exit code: 1
at scala.sys.package$.error(package.scala:27)
[trace] Stack trace suppressed: run last scala_cassandra_project_without_play/compile:run for the full output.
[error] (scala_cassandra_project_without_play/compile:run) Nonzero exit code: 1
[error] Total time: 0 s, completed 11-mar-2016 11:25:18
> 

正如您可以在我的build.sbt文件中看到的那样，我想使用一个彼此体面的多依赖项设置。

name := "My Project"

val commonSettings = Seq(
organization := "net.example",
version := "0.1",
scalaVersion := "2.11.4",
scalacOptions := Seq("-unchecked", "-deprecation", "-encoding", "utf8")
)

lazy val testDependencies = Seq (
"org.scalatest" %% "scalatest" % "2.2.0" % "test"
)

lazy val cassandraDependencies = Seq (
"com.datastax.cassandra" % "cassandra-driver-core" % "2.1.2",
"com.chrisomeara" % "pillar_2.11" % "2.0.1"
)

lazy val common = project.in(file("common"))
.settings(commonSettings:_*)
.settings(libraryDependencies ++= (testDependencies ++    cassandraDependencies))

val projectMainClass = "common.utils.cassandra.CassandraMain"

lazy val main = project.in(file("main"))
.dependsOn(common) 
.settings(commonSettings:_*)
.settings(
 mainClass := Some(projectMainClass)
)   

mainClass in (Compile, run) := Some(projectMainClass)

该项目的文件夹具有内部版本。根文件夹中的sbt文件，以及另外两个文件夹，common和main，具有相同的结构，我的意思是，

 aironman$:scala_cassandra_project_without_play ls common/src/main/scala/common/utils/cassandra/
CassandraConnectionUri.scala    Pillar.scala
Helper.scala

aironman$:scala_cassandra_project_without_play ls main/src/main/scala/common/utils/cassandra/
CassandraMain.scala

卡桑德拉明。scala代码太简单，只有包和主函数：

package common.utils.cassandra

import common.utils.cassandra._

object CassandraMain extends App{
    println("Trying to connect to Cassandra server...")
    //val uri = CassandraConnectionUri("cassandra://localhost:9042/test")
    //val session = Helper.createSessionAndInitKeyspace(uri)

    //session.execute(/* Some CQL string */)        
}

在@口渴行通知后更新1

我不理解为什么sbt试图寻找common_2.10，因为在commonSettings中scalaVersion设置为2.11.4，正如您所见，我的scala设置为：

MacBook-Pro-Retina-de-Alonso:~ aironman$ sbt sbtVersion
[info] Set current project to aironman (in build file:/Users/aironman/)
[info] 0.13.11
MacBook-Pro-Retina-de-Alonso:~ aironman$ scala -version
Scala code runner version 2.11.8 -- Copyright 2002-2016, LAMP/EPFL

好的，现在我知道main的懒val必须有. set（通用设置：_*），如果没有，它会尝试使用版本2.10

更新2，现在我知道我必须更改为project main并执行run命令。谢谢你们，斯奎特·克罗和纳比尔。

MacBook-Pro-Retina-de-Alonso:scala_cassandra_project_without_play aironman$ sbt
[info] Set current project to My Project (in build file:/Users/aironman/scala_cassandra_project_without_play/)
> project main
[info] Set current project to main (in build file:/Users/aironman/scala_cassandra_project_without_play/)
> run
[info] Running common.utils.cassandra.CassandraMain 
**Trying to connect to Cassandra server...**
[success] Total time: 1 s, completed 11-mar-2016 11:50:41

我学到了很多，再次感谢




Answer 1

似乎主体可能是文件名，但不是类名。更多信息，请张贴校长的内容。Scala类和文件名应该以后者开头
还要检查主类是否是对象。

Answer 2

CassandraMain在主项目中，您正在尝试在根项目中运行它。

为main项目设置main Class，并使用main/run在那里运行它。

lazy val main = project.in(file("main"))
  .dependsOn(common) // Should 'dependsOn' common if you wanna use common code in main
  .settings(
    mainClass := Some("common.utils.cassandra.CassandraMain")
  )