Generate Executable Jar for a Scala Project - scala

Question

I have a scala project which contain multiple main methods. I want to generate a fat jar so that I can run one of the main method related code.
build.sbt
lazy val commonSettings = Seq(
version := "0.1-SNAPSHOT",
organization := "my.company",
scalaVersion := "2.11.12",
test in assembly := {}
)
lazy val app = (project in file("app")).
settings(commonSettings: _*).
settings(
mainClass in assembly := Some("my.test.Category")
)
assemblyMergeStrategy in assembly := {
case "reference.conf" => MergeStrategy.concat
case "META-INF/services/org.apache.spark.sql.sources.DataSourceRegister" => MergeStrategy.concat
case PathList("META-INF", xs#_*) => MergeStrategy.discard
case _ => MergeStrategy.first
}
plugins.sbt
addSbtPlugin("com.eed3si9n" % "sbt-assembly" % "0.15.0")
By this Manifest file is generated successfully in my resource folder.
next I run sbt assembly and executable jar is generated successfully.
When i run java -jar category-assembly-0.1.jar i get the following error
no main manifest attribute, in category-assembly-0.1.jar
I tried many steps given in the internet but i keep getting this error
UPDATE
Currently following is included in my build.sbt.
lazy val spark: Project = project
.in(file("./spark"))
.settings(
mainClass in assembly := Some("my.test.Category"),
mainClass in (Compile, packageBin) := Some("my.test.Category"),
mainClass in (Compile, run) := Some("my.test.Category")
)
assemblyMergeStrategy in assembly := {
case "reference.conf" => MergeStrategy.concat
case "META-INF/services/org.apache.spark.sql.sources.DataSourceRegister" => MergeStrategy.concat
case PathList("META-INF", xs#_*) => MergeStrategy.discard
case _ => MergeStrategy.first
}
After building the artifacts and run the command sbt assembly and tried running the genrated jar im still getting the same error as follows
no main manifest attribute, in category-assembly-0.1.jar

Answer 1

I had the same issue when i was deploying on EMR.
Add the following to your setting in build.sbt and it will be alright.
lazy val spark: Project = project
.in(file("./spark"))
.settings(
...
// set the main class for packaging the main jar
mainClass in (Compile, packageBin) := Some("com.orgname.name.ClassName"),
mainClass in (Compile, run) := Some("com.orgname.name.ClassName"),
...
)
This essentially sets the name of your existing class in your project as default mainClass. i set both for packageBin and run so you should be alright.
Just don't forget to rename the com.orgname.name.ClassName to your classname.
(This is just to refresh your memory)
Classname consists of <PackageName>/<ClassName>.
For example:
package com.orgname.name
object ClassName {}