You can use defaultExpression in your mapping. It expects a string as an argument, with the following format:
"java(expression)"Where expression is the expression you're looking for, so in your case
@Mapping(source = "created", target = "created", defaultExpression = "java(java.time.Instant.now())")Notice that I used the fully qualified name for the Instant class, since defaultExpression can't know where Instant is (or at least it can't assume you want the one from the standard library), so it can't import it in the file it generates.