Model Variant Generator - Java

This library consists of a Java annotation processor that generates variants based on given Java models.

Maven

Add this library as a compile dependency. It will be called during compilation.

<dependency>
    <groupId>de.gofabian</groupId>
    <artifactId>model-variant-parent</artifactId>
    <version>0.1.0</version>
    <scope>compile</scope>
</dependency>

Example

Imagine you want to have multiple variants of a domain model, e.g. to represent inputs for creating and updating the original domain model.

Imagine you want to:

• have an original model containing all fields,
• have a create variant that does not contain generated fields (e.g. id, createdAt),
• have an update variant that contains the id but no other generated fields (e.g. createdAt).

You can do that by adding annotations to the original model:

import de.gofabian.modelvariant.annotation.FieldVariant;

record Model(
        @FieldVariant(name = "Update")
        int id,

        @FieldVariant(name = "Create")
        @FieldVariant(name = "Update")
        String name,

        OffsetDateTime createdAt
) {
}

This library will fulfill your requirements by generating the following variants during compilation:

record ModelCreateVariant(
        String name
) {
}

record ModelUpdateVariant(
        int id,
        String name
) {
}

How does it work?

• The generator is a Java annotation processor.
• It is called during compilation.
• It reads the variant annotations and generates variants accordingly.
• The variants can be used in your code.
• The generator itself will not be part of the bytecode if you add it with compile scope.

Next Steps

Release 0.2+:

• takeover original nullabililty
  • part of Variant field annotation
  • read jetbrains notnull/nullable annotations
  • produce jetbrains notnull/nullable annotations
• configure immutability
  • class annotation
  • immutable by default: Java records
  • mutable: custom Java class
• processor configuration?
  • global options to set e.g.
  • unmodifiable = true/false
  • @SupportedOptions("key"), add compiler arg in maven-compiler-plugin -Akey=value, processingEnv.getOptions().get(" key")