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")
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
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.
bashScriptConfigLocation
- The location of the bash script on the target system. Default
${app_home}/../conf/application.ini
batScriptConfigLocation
- The location of the bat script on the target system. Default
%APP_HOME%\conf\application.ini
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.
- A start script for each entry point. This is the default behaviour, when no
mainClass in Compile
is set - 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.
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
becomes
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.