为什么生成的清单中没有 Main-Class 属性？

Question

我有一个包含程序集插件的 build.sbt 文件。直到最近的构建，Main-Class 属性都包含在组装的 far jar 中，但突然之间，情况不再如此。

当我尝试运行 jar 时，我得到了无与伦比的：

no main manifest attribute, in ./target/scala-2.10/foo-0.3.0-SNAPSHOT.jar

但是使用 sbt 控制台运行，效果很好。

我的 build.sbt 目前看起来像这样（在程序集中添加 mainClass 是为了强制向程序集插件指示它确实应该包含，尽管我在插件源代码中注意到，它看起来像是在检查指定的无论如何都要运行）。

import AssemblyKeys._

name := "foo"

version := "0.3.0-SNAPSHOT"

organization := "com.mycompany.myproduct"

scalaVersion := "2.10.4"

mainClass in (Compile, run) := Some("ProcessRelogger")

mainClass in assembly := Some("ProcessRelogger")

assemblySettings

libraryDependencies ++= Seq(
  "org.scalatest" % "scalatest_2.10" % "1.9.2" % "test",
  "ch.qos.logback" % "logback-classic" % "1.0.9",
  "com.typesafe.akka" %% "akka-actor" % "2.2.4",
  "joda-time" % "joda-time" % "2.3",
  "com.rabbitmq" % "amqp-client" % "3.3.4",
  "org.scalaz" % "scalaz-core_2.10" % "7.0.6",
  "com.typesafe.slick" %% "slick" % "2.0.2",
  "postgresql" % "postgresql" % "9.1-901.jdbc4",
  "com.escalatesoft.subcut" %% "subcut" % "2.0"
)

当我解压 jar 文件并检查 META-INF/MANIFEST.MF 时，没有包含 Main-Class: 属性。

Answer 1

这是尝试使用最新版本的sbt-assembly 0.11.2 重现该问题。

project/build.properties

sbt.version=0.13.7-M3

project/assembly.sbt

addSbtPlugin("com.eed3si9n" % "sbt-assembly" % "0.11.2")

build.sbt

import AssemblyKeys._

assemblySettings

scalaVersion := "2.11.2"

src/main/scala/Main.scala

object HelloApp extends App {
  println("Hello")
}

将以上所有文件放在一个项目中：

> about
[info] Updating {file:/Users/jacek/sandbox/sbt-assembly/}sbt-assembly...
[info] Resolving jline#jline;2.12 ...
[info] Done updating.
[info] This is sbt 0.13.7-M3
[info] The current project is {file:/Users/jacek/sandbox/sbt-assembly/}sbt-assembly 0.1-SNAPSHOT
[info] The current project is built against Scala 2.11.2
[info] Available Plugins: sbt.plugins.IvyPlugin, sbt.plugins.JvmPlugin, sbt.plugins.CorePlugin, sbt.plugins.JUnitXmlReportPlugin, com.typesafe.sbteclipse.plugin.EclipsePlugin, net.virtualvoid.sbt.graph.Plugin, com.github.tototoshi.sbt.musical.Plugin, com.timushev.sbt.updates.UpdatesPlugin, sbtassembly.Plugin
[info] sbt, sbt plugins, and build definitions are using Scala 2.10.4

> assembly
[info] Updating {file:/Users/jacek/sandbox/sbt-assembly/}sbt-assembly...
[info] Resolving jline#jline;2.12 ...
[info] Done updating.
[info] Compiling 1 Scala source to /Users/jacek/sandbox/sbt-assembly/target/scala-2.11/classes...
[info] Including: scala-library-2.11.2.jar
[info] Checking every *.class/*.jar file's SHA-1.
[info] Merging files...
[warn] Merging 'META-INF/MANIFEST.MF' with strategy 'discard'
[warn] Strategy 'discard' was applied to a file
[info] SHA-1: a5c09d7626fe19f4e3cd98d709966a77f127b048
[info] Packaging /Users/jacek/sandbox/sbt-assembly/target/scala-2.11/sbt-assembly-assembly-0.1-SNAPSHOT.jar ...
[info] Done packaging.
[success] Total time: 4 s, completed Oct 8, 2014 9:27:41 AM

> eval "unzip -p target/scala-2.11/sbt-assembly-assembly-0.1-SNAPSHOT.jar META-INF/MANIFEST.MF" !
Manifest-Version: 1.0
Implementation-Title: sbt-assembly
Implementation-Version: 0.1-SNAPSHOT
Specification-Vendor: default
Specification-Title: sbt-assembly
Implementation-Vendor-Id: default
Specification-Version: 0.1-SNAPSHOT
Main-Class: HelloApp
Implementation-Vendor: default

[info] ans: Int = 0

Answer 2

这并不能回答原始问题的“为什么”，但正如其他 cmets 所提到的，如果您引入另一个 main（例如通过另一个对象间接包括），就会发生这种情况。

因此您可以在 build.sbt 中明确定义它：

mainClass in assembly := Some("path.to.intended.Main")  // object with main

Answer 3

尝试在 (Compile, run) 中注释掉 mainClass := Some("ProcessRelogger") ]$ sbt clean assembly ]$ java -jar target/xxx.jar