在sbt中为Scala项目实施Java版本？

Question

我的scala应用程序只能运行Java 7,因为它依赖于只出现在该版本的JDK中的库.

如何在sbt中强制执行该操作,以便在启动sbt运行/编译应用程序时使用错误版本的Java时,会立即向用户显示正确的错误消息？

注意:此处无编译Java™源代码.我只有 Scala源代码.Scala代码需要import java.nio.file.PathJava 7提供的代码.

Answer 1

javacOptions ++= Seq("-source", "1.7", "-target", "1.7")如果没有Java源,则使用不起作用.

但是您可以在build.sbt或Build.scala中为Scala编译器设置目标JVM:

scalacOptions += "-target:jvm-1.7"

结果它在JDK 6上打印:

$ sbt clean run
[info] Set current project to default-cd5534 (in build file:/tmp/so/)
[success] Total time: 0 s, completed 27.10.2013 14:31:43
[info] Updating {file:/tmp/so/}default-cd5534...
[info] Resolving org.fusesource.jansi#jansi;1.4 ...
[info] Done updating.
[info] Compiling 1 Scala source to /tmp/so/target/scala-2.10/classes...
[info] Running Main 
[error] (run-main) java.lang.UnsupportedClassVersionError: Main : Unsupported major.minor version 51.0
java.lang.UnsupportedClassVersionError: Main : Unsupported major.minor version 51.0
        at java.lang.ClassLoader.defineClass1(Native Method)
        at java.lang.ClassLoader.defineClass(ClassLoader.java:634)
        at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
        at java.net.URLClassLoader.defineClass(URLClassLoader.java:277)
        at java.net.URLClassLoader.access$000(URLClassLoader.java:73)
        at java.net.URLClassLoader$1.run(URLClassLoader.java:212)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.net.URLClassLoader.findClass(URLClassLoader.java:205)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:321)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:314)
[trace] Stack trace suppressed: run last compile:run for the full output.
java.lang.RuntimeException: Nonzero exit code: 1
        at scala.sys.package$.error(package.scala:27)
[trace] Stack trace suppressed: run last compile:run for the full output.
[error] (compile:run) Nonzero exit code: 1
[error] Total time: 4 s, completed 27.10.2013 14:31:47

注意:也许它仅适用于最新的SBT/Scalac版本.

Answer 2

作为Scala代码,您可以在构建定义中放置断言.sbt将此类定义initialize为常见的地方,但您可以使用任何设置,包括自定义设置.例如,

initialize := {
   val _ = initialize.value // run the previous initialization
   val classVersion = sys.props("java.class.version")
   val specVersion = sys.props("java.specification.version")
   assert(..., "Java N or above required")
}

Answer 3

对于未来的任何人来说,这也是一个很好的方法.如果找不到合适的Java版本,它会立即停止执行:

initialize := {
  val _ = initialize.value // run the previous initialization
  val required = "1.8"
  val current  = sys.props("java.specification.version")
  assert(current == required, s"Unsupported JDK: java.specification.version $current != $required")
}

你把它放在你的build.sbt.

Answer 4

在SBT 0.13.6中有一个新的VersionNumber类和VersionNumberCompatibility特征.调整@MarkHarrah建议使用此方法的方法可能会执行以下操作:

initialize := {
    val _ = initialize.value // run the previous initialization
    val required = VersionNumber("1.8")
    val curr = VersionNumber(sys.props("java.specification.version"))
    assert(CompatibleJavaVersion(curr, required), s"Java $required or above required")
}

...
/** Java specification version compatibility rule. */
object CompatibleJavaVersion extends VersionNumberCompatibility {
    def name = "Java specification compatibility"
    def isCompatible(current: VersionNumber, required: VersionNumber) =
        current.numbers.zip(required.numbers).foldRight(required.numbers.size<=current.??numbers.size)((a,b) => (a._1 > a._2) || (a._1==a._2 && b))
    def apply(current: VersionNumber, required: VersionNumber) = isCompatible(current, required)
}

Answer 5

为了在 Java 7 中编译，您应该添加 javac 选项以使用源 1.7 进行编译。

您应该添加javacOptions ++= Seq("-source", "1.7")到 /project 文件夹中的 SBT 构建配置。

以下是 SBT 的参考： http://www.scala-sbt.org/release/docs/Detailed-Topics/Java-Sources.html