Java is officially supported on Scalingo

Java Versions

Availability

The following Java versions are available:

For Java SE 8, the JDK version is numbered 1.8.

Selecting a Version

The default Java version on both scalingo-20 (deprecated) and scalingo-22 is the latest 1.8. You can, however, instruct the platform to use another version.

To do so, specify the version number in a file called system.properties, which must be stored at the root of the project directory, like so:

java.runtime.version=<version>

Please replace <version> with the actual number you want. For example, to install the latest version of OpenJDK 15:

java.runtime.version=15

Frameworks

Most frameworks should work on the platform, the only condition is to listen on the port defined by the environment variable PORT

• Spring Boot: You can find custom information about this framework at the following page

Languages Using the JVM

Even though the Java Virtual Machine (JVM) was initially designed to execute program developed with Java, a lot of new languages have been developed to be executed on it. Most of them should work on Scalingo. Here are examples of such languages known to work on Scalingo:

• Scala: see the specific documentation page here.
• Groovy: see the specific documentation page here.
• Clojure: see the specific documentation page here.
• Kotlin: see the sample deployed here, and the source code.

Deployment

It uses Maven 3.9.4 to build your application and OpenJDK 1.8 to run it (by default).

Example usage:

$ ls
Procfile  pom.xml  src

$ scalingo create my-app

$ git push scalingo master
...
-----> Java app detected
-----> Installing OpenJDK 1.8... done
-----> Installing Maven 3.3.9... done
-----> Installing settings.xml... done
-----> executing /app/tmp/repo.git/.cache/.maven/bin/mvn -B -Duser.home=/tmp/build_19z6l4hp57wqm -Dmaven.repo.local=/app/tmp/repo.git/.cache/.m2/repository -s /app/tmp/repo.git/.cache/.m2/settings.xml -DskipTests=true clean install
       [INFO] Scanning for projects...
       [INFO]
       [INFO] ------------------------------------------------------------------------
       [INFO] Building readmeTest 1.0-SNAPSHOT
       [INFO] ------------------------------------------------------------------------
...

The buildpack will detect your app as Java if it has the file pom.xml in the root. It will use Maven to execute the build defined by your pom.xml and download your dependencies.

If your build results in a .war file you need to add a small dependency to your project in order to execute it. Just follow the guide.

The .m2 folder (local maven repository) will be cached between builds for faster dependency resolution. However neither the mvn executable nor the .m2 folder will be available in your slug at runtime.

Configuration

Default JVM Configuration

By default the -Xmx configuration of the JVM depends on the size of container you selected for your application:

Choose a Maven Version

The system.properties file also allows for maven.version entry (regardless of whether you specify a java.runtime.version entry). For example:

java.runtime.version=14
maven.version=3.2.5

Supported versions of Maven are:

• 3.0.5
• 3.1.1
• 3.2.5
• 3.3.9
• 3.5.4
• 3.6.2
• 3.9.4

You can request new versions of Maven by submitting a pull request to the Java buildpack against the lib/common.sh file.

Customize Maven

There are two environment variables that can be used to customize the Maven execution:

• MAVEN_CUSTOM_GOALS: set to clean install by default
• MAVEN_CUSTOM_OPTS: set to -DskipTests=true by default

These variables can be set like this:

$ scalingo env-set MAVEN_CUSTOM_GOALS="clean package"
$ scalingo env-set MAVEN_CUSTOM_OPTS="--update-snapshots -DskipTests=true"

Other options are available for defining custom a settings.xml file.

Installation of JDK only (no Maven)

Your application may need to have the JDK/JVM only and not installing any dependency, in this case you should use the multi-buildpack. The .buildpacks file lists the buildpacks you need to use, it has to look like:

https://github.com/Scalingo/buildpack-jvm-common
[Your second buildpack]

The role of the JVM Common buildpack to install it according to the system.properties file as mentionned above in this page.

Add a custom CA to Java Keychain

You may need to add one or multiple custom certificates to your JDK’s Keychain. You need to download Scalingo default JDK cacerts, then add the custom certificates you’d like to add with the following command:

keytool -import -keystore cacerts -file custom.cer

Then create the following directory in your application .jdk-overlay/jre/lib/security/ and move the cacerts keystore file to it. Add it to your repository, and that’s it! Your custom CAs will be taken into account.

Buildpack

More information at https://github.com/Scalingo/java-buildpack.