einherjar

A Java tool that transforms a Java jar to an Einherjar to go to Valhalla.

einherjar is a simple Java tool that takes a jar with classes annotated with the annotation @ValueType (or your own annotation), checks that the annotated classes can be value classes and generate an Einherjar.

An Einherjar, the generated jar, is a Multi-Release jar that

• run as usual with any VM able to run the input jar,
• run the annotated classes seen as value classes with a Valhalla enabled VM (and '--enable-preview').

To build einherjar, use maven

With any Java 21+ distribution.

  mvn package

generates a file named einherjar.jar in target.

To run einherjar

With any Java 8+ distribution.

Running einherjar with no action, prints the help

  java -jar target/einherjar.jar

einherjar provides several actions:

• find that helps you find the potential value classes,
• check that verifies that the annotated classes can be transformed to value classes,
• enhance that generates the Einherjar.

and several options:

• --annotation name to set the name of the annotation (e.g. com.github.forax.einherjar.api.ValueType)
• --classes names to set the name of classes to be checked/enhanced (e.g. com.acme.Foo,com.acme.Bar)
• --output path to set the name of the generated Einherjar
• --version version to set the classfile version of the generated value classes (always in preview)