Java Application Archetype

Application packaging focuses on how your application is launched (via a bash or bat script), how dependencies are managed and how configuration and other auxiliary files are included in the final distributable. The JavaAppPackaging archetype provides a default application structure and executable scripts to launch your application.

Additionally there is Java Server Application Archetype which provides platform-specific functionality for installing your application in server environments. You can customize specific debian and rpm packaging for a variety of platforms and init service loaders including Upstart, System V and SystemD.

Features

The JavaAppPackaging archetype contains the following features.

  • Default application mappings (no fat jar)
  • Executable bash/bat script

Usage

Enable the JavaAppPackaging plugin in your build.sbt with

enablePlugins(JavaAppPackaging)

This archetype will use the mainClass setting of sbt (automatically discovers your main class) to generate bat and bin scripts for your project. In case you have multiple main classes you can point to a specific class with the following setting:

mainClass in Compile := Some("foo.bar.Main")

To create a staging version of your package call

sbt stage

The universal layout produced in your target/universal/stage folder looks like the following:

bin/
  <app_name>       <- BASH script
  <app_name>.bat   <- cmd.exe script
lib/
   <Your project and dependent jar files here.>

You can add additional files to the project by placing things in src/windows, src/universal or src/linux as needed. To see if your application runs:

cd target/universal/stage
./bin/<app-name>

This plugin also enables all supported packaging formats as well. Currently all formats are supported by the java app archetype! For example you can build zips, deb or docker by just enabling JavaAppPackaging.

sbt
# create a zip file
> universal:packageBin
# create a deb file
> debian:packageBin
# publish a docker image to your local registry
> docker:publishLocal

Settings & Tasks

This is a non extensive list of important settings and tasks this plugin provides. All settings have sensible defaults.

makeBashScript
Creates or discovers the bash script used by this project.
makeBatScript
Creates or discovers the bat script used by this project.
bashScriptTemplateLocation
The location of the bash script template.
batScriptTemplateLocation
The location of the bat script template.
bashScriptExtraDefines
A list of extra definitions that should be written to the bash file template.
batScriptExtraDefines
A list of extra definitions that should be written to the bat file template.

Start script options

The start script provides a few standard options you can pass:

-h | -help
Prints script usage
-v | -verbose
Prints out more information
-no-version-check
Don’t run the java version check
-jvm-debug <port>
Turn on JVM debugging, open at the given port
-java-home <java home>
Override the default JVM home, it accept variable expansions, e.g. -java-home ${app_home}/../jre
-main
Define a custom main class

To configure the JVM these options are available

JAVA_OPTS
environment variable, if unset uses “$java_opts”
-Dkey=val
pass -Dkey=val directly to the java runtime
-J-X
pass option -X directly to the java runtime (-J is stripped). E.g. -J-Xmx1024

In order to pass application arguments you need to separate the jvm arguments from the application arguments with --. For example

./bin/my-app -Dconfig.resource=prod.conf -- -appParam1 -appParam2

Multiple Applications

If you have multiple main classes then the JavaAppPackaging archetype provides you with two different ways of generating start scripts.

  1. A start script for each entry point. This is the default behaviour, when no mainClass in Compile is set
  2. One start script for the defined mainClass in Compile and forwarding scripts for all other main classes.

Note

What does ‘forwarder script’ mean?

Native-packager’s start script provides a -main option to override the main class that should be executed. A forwarder script only overrides this attribute and forwards all other parameters to the normal start script.

All customization you implemented for the main script will also apply for the forwarder scripts.

Multiple start scripts

No configuration is needed. SBT sets mainClass in Compile automatically to None if multiple main classes are discovered.

Example:

For two main classes com.example.FooMain and com.example.BarMain sbt stage will generate these scripts:

bin/
  bar-main
  bar-main.bat
  foo-main
  foo-main.bat

Single start script with forwarders

Generates a single start script for the defined main class in mainClass in Compile and forwarding scripts for all other discoveredMainClasses in Compile. The forwarder scripts call the defined start script and set the -main parameter to the concrete main class.

The start script name uses the executableScriptName setting for its name. The forwarder scripts use a simplified version of the class name.

Example:

The build.sbt has an explicit main class set.

name := "my-project"
mainClass in Compile := Some("com.example.FooMain")

For two main classes com.example.FooMain and com.example.BarMain sbt stage will generate these scripts:

bin/
  bar-main
  bar-main.bat
  my-project
  my-project.bat

Now you can package your application as usual, but with multiple start scripts.