scala sbt assembly “no main manifest attribute”

Question

I use assembly plugin in sbt to assemble my project. But errors happen when run by "java -jar xx.jar" -

"no main manifest attribute".

I think it's because there are two files in my src/main/scala/ directory and each with an object extending Application which means there are two main entry in the project. But I need two applications, one is the server and the other is the test client.

How to handle this two-main-entry problem in scala sbt. Thanks in advance.

Answer 1

In your SBT build file, define the main class.

If you are using build.sbt, then that would be:

mainClass in assembly := Some("com.domain.Main")

If you are using Build.scala then you could do something like:

lazy val app = (project in file("app")).
  settings(assemblySettings: _*)
  settings(mainClass in assembly := Some("com.domain.Main"))

Answer 2

You can use -cp instead of -jar

java -cp xx.jar com.domain.AnyClassName

Answer 3

I had this issue while testing out Lagom.

To deploy in Lagom you can just access the -impl project and run this:

./sbt "project <your-project>-impl" dist

This will generate a zip with the executable inside.