sbt-assembly

Deploy fat JARs. Restart processes.

sbt-assembly is a sbt plugin originally ported from codahale's assembly-sbt, which I'm guessing was inspired by Maven's assembly plugin. The goal is simple: Create a fat JAR of your project with all of its dependencies.

Requirements

• sbt
• The burning desire to have a simple deploy procedure.

Reporting Issues & Contributing

Before you email me, please read Issue Reporting Guideline carefully. Twice. (Don't email me)

Setup

Using Published Plugin

For sbt 0.13 add sbt-assembly as a dependency in project/assembly.sbt:

addSbtPlugin("com.eed3si9n" % "sbt-assembly" % "0.11.1")

For sbt 0.12, see sbt-assemlby 0.9.2.

(You may need to check this project's tags to see what the most recent release is.)

Usage

Applying the plugin to a project (Adding the assembly Task)

First, make sure that you've added the plugin to your build (either the published builds or source from Git).

Put assembly.sbt at the root directory:

import AssemblyKeys._ // put this at the top of the file

assemblySettings

// your assembly settings here

Applying the plugin to multi-project build.sbt

If you are using multi-project build.sbt:

import AssemblyKeys._

lazy val buildSettings = Seq(
  version := "0.1-SNAPSHOT",
  organization := "com.example",
  scalaVersion := "2.10.1"
)

val app = (project in file("app")).
  settings(buildSettings: _*).
  settings(assemblySettings: _*).
  settings(
    // your settings here
  )

Applying the plugin to multi-project build.scala

If you are using multi-project build.scala:

import sbt._
import Keys._
import sbtassembly.Plugin._
import AssemblyKeys._

object Builds extends Build {
  lazy val buildSettings = Defaults.defaultSettings ++ Seq(
    version := "0.1-SNAPSHOT",
    organization := "com.example",
    scalaVersion := "2.10.1"
  )

  lazy val app = Project("app", file("app"),
    settings = buildSettings ++ assemblySettings) settings(
      // your settings here
    )
}

assembly task

Now you'll have an awesome new assembly task which will compile your project, run your tests, and then pack your class files and all your dependencies into a single JAR file: target/scala_X.X.X/projectname-assembly-X.X.X.jar.

> assembly

If you specify a mainClass in assembly in build.sbt (or just let it autodetect one) then you'll end up with a fully executable JAR, ready to rock.

Here is the list of the keys you can rewire for assembly task.

NOTE: Any customization must be written after assemblySettings.

jarName                       test                          mainClass
outputPath                    mergeStrategy                 assemblyOption
excludedJars                  assembledMappings

For example the name of the jar can be set as follows in build.sbt:

jarName in assembly := "something.jar"

To skip the test during assembly,

test in assembly := {}

To set an explicit main class,

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

Merge Strategy

If multiple files share the same relative path (e.g. a resource named application.conf in multiple dependency JARs), the default strategy is to verify that all candidates have the same contents and error out otherwise. This behavior can be configured on a per-path basis using either one of the following built-in strategies or writing a custom one:

• MergeStrategy.deduplicate is the default described above
• MergeStrategy.first picks the first of the matching files in classpath order
• MergeStrategy.last picks the last one
• MergeStrategy.singleOrError bails out with an error message on conflict
• MergeStrategy.concat simply concatenates all matching files and includes the result
• MergeStrategy.filterDistinctLines also concatenates, but leaves out duplicates along the way
• MergeStrategy.rename renames the files originating from jar files
• MergeStrategy.discard simply discards matching files

The mapping of path names to merge strategies is done via the setting assembly-merge-strategy which can be augmented as follows:

mergeStrategy in assembly <<= (mergeStrategy in assembly) { (old) =>
  {
    case PathList("javax", "servlet", xs @ _*)         => MergeStrategy.first
    case PathList(ps @ _*) if ps.last endsWith ".html" => MergeStrategy.first
    case "application.conf" => MergeStrategy.concat
    case "unwanted.txt"     => MergeStrategy.discard
    case x => old(x)
  }
}

NOTE:

• mergeStrategy in assembly expects a function, you can't do mergeStrategy in assembly := MergeStrategy.first!
• Some files must be discarded or renamed otherwise, you're breaking the zip or legal license. Use the pattern above.

By the way, the first case pattern in the above using PathList(...) is how you can pick javax/servlet/* from the first jar. If the default MergeStrategy.deduplicate is not working for you, that likely means you have multiple versions of some library pulled by your dependency graph. The real solution is to fix that dependency graph. You can work around it by MergeStrategy.first but don't be surprised when you see ClassNotFoundException.

Here is the default:

  val defaultMergeStrategy: String => MergeStrategy = { 
    case x if Assembly.isConfigFile(x) =>
      MergeStrategy.concat
    case PathList(ps @ _*) if Assembly.isReadme(ps.last) || Assembly.isLicenseFile(ps.last) =>
      MergeStrategy.rename
    case PathList("META-INF", xs @ _*) =>
      (xs map {_.toLowerCase}) match {
        case ("manifest.mf" :: Nil) | ("index.list" :: Nil) | ("dependencies" :: Nil) =>
          MergeStrategy.discard
        case ps @ (x :: xs) if ps.last.endsWith(".sf") || ps.last.endsWith(".dsa") =>
          MergeStrategy.discard
        case "plexus" :: xs =>
          MergeStrategy.discard
        case "services" :: xs =>
          MergeStrategy.filterDistinctLines
        case ("spring.schemas" :: Nil) | ("spring.handlers" :: Nil) =>
          MergeStrategy.filterDistinctLines
        case _ => MergeStrategy.deduplicate
      }
    case _ => MergeStrategy.deduplicate
  }

Custom MergeStrategys can find out where a particular file comes from using the sourceOfFileForMerge method on sbtassembly.AssemblyUtils, which takes the temporary directory and one of the files passed into the strategy as parameters.

Excluding JARs and files

If you need to tell sbt-assembly to ignore JARs, you're probably doing it wrong. assembly task grabs deps JARs from your project's classpath. Try fixing the classpath first.

% "provided" configuration

If you're trying to exclude JAR files that are already part of the container (like Spark), consider scoping the dependent library to "provided" configuration:

libraryDependencies += Seq(
  "org.apache.spark" %% "spark-core" % "0.8.0-incubating" % "provided",
  "org.apache.hadoop" % "hadoop-client" % "2.0.0-cdh4.4.0" % "provided"
)

Maven defines "provided" as:

This is much like compile, but indicates you expect the JDK or a container to provide the dependency at runtime. For example, when building a web application for the Java Enterprise Edition, you would set the dependency on the Servlet API and related Java EE APIs to scope provided because the web container provides those classes. This scope is only available on the compilation and test classpath, and is not transitive.

The dependency will be part of compilation and test, but excluded from the runtime. If you Spark people want to include "provided" dependencies back to run, @douglaz has come up with a one-liner solution on StackOverflow sbt: how can I add "provided" dependencies back to run/test tasks' classpath?:

run in Compile <<= Defaults.runTask(fullClasspath in Compile, mainClass in (Compile, run), runner in (Compile, run)) 

Exclude specific transitive deps

You might be thinking about exluding JAR files because of the merge conlifcts. Merge conflict of *.class files indicate pathological classpath, often due to non-modular bundle JAR files or SLF4J, not the problem with assembly. Here's what happens when you try to create a fat JAR with Spark included:

[error] (*:assembly) deduplicate: different file contents found in the following:
[error] /Users/foo/.ivy2/cache/org.eclipse.jetty.orbit/javax.servlet/orbits/javax.servlet-2.5.0.v201103041518.jar:javax/servlet/SingleThreadModel.class
[error] /Users/foo/.ivy2/cache/org.mortbay.jetty/servlet-api/jars/servlet-api-2.5-20081211.jar:javax/servlet/SingleThreadModel.class

In the above case two separate JAR files javax.servlet-2.5.0.v201103041518.jar and servlet-api-2.5-20081211.jar are defining javax/servlet/SingleThreadModel.class! Similarly also conlifcts on common-beanutils and EsotericSoftware/minlog. Here's how to evict specific transitive deps:

libraryDependencies ++= Seq(
  ("org.apache.spark" %% "spark-core" % "0.8.0-incubating").
    exclude("org.mortbay.jetty", "servlet-api").
    exclude("commons-beanutils", "commons-beanutils-core").
    exclude("commons-collections", "commons-collections").
    exclude("commons-collections", "commons-collections").
    exclude("com.esotericsoftware.minlog", "minlog")
)

See sbt's Exclude Transitive Dependencies for more details.

Sometimes it takes a bit of detective work to figure out which transitive deps to exclude. Play! comes with dist task, so assembly is not needed, but suppose we wanted to run assembly. It brings in signpost-commonshttp4, which leads to commons-logging. This conflicts with jcl-over-slf4j, which re-implements the logging API. Since the deps are added via build.sbt and playScalaSettings, here's one way to work around it:

libraryDependencies ~= { _ map {
  case m if m.organization == "com.typesafe.play" =>
    m.exclude("commons-logging", "commons-logging").
      exclude("com.typesafe.play", "sbt-link")
  case m => m
}}

Excluding specific files

To exclude specific files, customize merge strategy:

mergeStrategy in assembly <<= (mergeStrategy in assembly) { (old) =>
  {
    case PathList("about.html") => MergeStrategy.rename
    case x => old(x)
  }
}

Excluding Scala library, your project, or deps JARs

To exclude Scala library,

assemblyOption in assembly ~= { _.copy(includeScala = false) }

To exclude the class files from the main sources and internal dependencies,

assemblyOption in assembly ~= { _.copy(includeBin = false) }

To make a JAR file containing only the external dependencies, type

> assemblyPackageDependency

NOTE: If you use -jar option for java, it will ignore -cp, so if you have multiple JAR files you have to use -cp and pass the main class: java -cp "jar1.jar:jar2.jar" Main

excludedJars

If all efforts fail, here's a way to exclude JAR files:

excludedJars in assembly <<= (fullClasspath in assembly) map { cp => 
  cp filter {_.data.getName == "compile-0.1.0.jar"}
}

Other Things

Content hash

You can also append SHA-1 fingerprint to the assembly file name, this may help you to determine whether it has changed and, for example, if it's necessary to deploy the dependencies,

assemblyOption in packageDependency ~= { _.copy(appendContentHash = true) }

Caching

By default for performance reasons, the result of unzipping any dependency JAR files to disk is cached from run-to-run. This feature can be disabled by setting:

assemblyOption in assembly ~= { _.copy(cacheUnzip = false) }

In addition the fat JAR is cached so its timestamp changes only when the input changes. This feature requires checking the SHA-1 hash of all *.class files, and the hash of all dependency *.jar files. If there are a large number of class files, this could take a long time, although with hashing of jar files, rather than their contents, the speed has recently been improved. This feature can be disabled by setting:

assemblyOption in assembly ~= { _.copy(cacheOutput = false) }

Publishing (Not Recommended)

Publishing fat JARs out to the world is discouraged because non-modular JARs cause much sadness. One might think non-modularity is convenience but it quickly turns into a headache the moment your users step outside of Hello World example code. If you still wish to publish your assembled artifact along with the publish task and all of the other artifacts, add an assembly classifier (or other):

artifact in (Compile, assembly) ~= { art =>
  art.copy(`classifier` = Some("assembly"))
}

addArtifact(artifact in (Compile, assembly), assembly)

Prepending Shebang

You can prepend shell script to the fat jar as follows:

assemblyOption in assembly ~= { _.copy(prependShellScript = Some(defaultShellScript)) }

jarName in assembly := { s"${name.value}-${version.value}" }

This will prepend the following shell script to the jar.

#!/usr/bin/env sh
exec java -jar "$0" "$@"

License

Copyright (c) 2010-2014 e.e d3si9n, Coda Hale

Published under The MIT License, see LICENSE