LinkTypeExt.java

public class LinkTypeExt extends Extension<Optional<String>>{
    @Override
    public Optional<String> extract(ObjectNode node) {
        return node.has("type") ? Optional.some(node.get("type").asText()) : Optional.<String>none();
    }

    @Override
    public Map<String, JsonNode> apply(Optional<String> value) {
        if (value.isSome()) {
            return Collections.singletonMap("type", ValueFactory.createValue(value.get()).asJson());
        }
        return Collections.emptyMap();
    }

    public static void main(String[] args) {
        Collection c = ...;

        Optional<Link> alternate = c.linkByRel("alternate");
        for (Link link : alternate) {
            Optional<String> typeOpt = link.getExtension(new LinkTypeExt());
            for (String type : typeOpt) {
                System.out.println("type = " + type);
            }
        }
    }
}