Java Application Archetype¶
Application packaging focuses on how your application is launched (via a
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.
The JavaAppPackaging archetype contains the following features.
- Default application mappings (no fat jar)
- Executable bash/bat script
JavaAppPackaging plugin in your
This archetype will use the
mainClass setting of sbt (automatically discovers your main class) to generate
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")
In order to generate launch scripts only for specified
mainClass, you will need to discard automatically found main classes:
discoveredMainClasses in Compile := Seq()
To create a staging version of your package call
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
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
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.
- Creates or discovers the bash script used by this project.
- Creates or discovers the bat script used by this project.
- The location of the bash script template.
- The location of the bat script template.
- The location of the bash script on the target system. Default
- The location of the bat script on the target system. Default
- A list of extra definitions that should be written to the bash file template.
- 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
- Don’t run the java version check
- Turn on JVM debugging, open at the given port
-java-home <java home>
- Override the default JVM home, it accept variable expansions, e.g.
- Define a custom main class
To configure the JVM these options are available
- environment variable, if unset uses “$java_opts”
- pass -Dkey=val directly to the java runtime
- pass option -X directly to the java runtime (-J is stripped). E.g.
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
If you have multiple main classes then the
JavaAppPackaging archetype provides you with two different ways of
generating start scripts.
- A start script for each entry point. This is the default behaviour, when no
mainClass in Compileis set
- One start script for the defined
mainClass in Compileand forwarding scripts for all other main classes.
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
For two main classes
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
discoveredMainClasses in Compile. The forwarder scripts call the defined start script and set the
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.
build.sbt has an explicit main class set.
name := "my-project" mainClass in Compile := Some("com.example.FooMain")
For two main classes
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.
A note on script names¶
When this plugin generates script names from main class names, it tries to generate readable and unique names:
An heuristic is used to split the fully qualified class names into words:
pkg1.TestClass pkg2.AnUIMainClass pkg2.SomeXMLLoader pkg3.TestClass
pkg-1.test-class pkg-2.an-ui-main-class pkg-2.some-xml-loader pkg-3.test-class
Resulted lower-cased names are grouped by the simple class name.
- Names from single-element groups are reduced to their lower-cased simple names.
- Names that would otherwise collide by their simple names are used as is (that is, full names) with dots replaced by underscores
So the final names will be:
pkg-1_test-class an-ui-main-class some-xml-loader pkg-3_test-class
Please note that in some corner cases this may result in multiple scripts with the same name in the resulting archive, but it is not expected to happen in normal circumstances.