ActivityStreams4J is a Java library consisting of DTOs for the W3C ActivityStreams 2.0 specification, along with the ActivityPub extension.
These DTOs are annotated with Java OWL Persistence API (JOPA) annotations, designed to work with Java Binding for JSON-LD and automatically tested against the example inputs from the W3C technical reports for ActivityStreams Core, ActivityStreams Vocabulary and ActivityPub.