Constructor annotation on java records

Question

Is there a way to get an annotation like ConstructorProperties that has @Target(CONSTRUCTOR) to annotate the generated constructor of a java 16 record? E.g.:

@ConstructorProperties({"id", "filename"})
public record Person(long id, String filename) {}

This ^ causes the following error:

java: annotation type not applicable to this kind of declaration

Johnsen

Answer 1

This worked:

public record Person(long id, String filename) {
    @ConstructorProperties({"id", "filename"})
    public Person {}
}

My understanding is that the inner constructor with no parameter list is a way of adding logic to the default constructor created using the component list. Apparently, adding a constructor annotation to that has the end result I was after :)

Johnsen

Yes, this is the recommended solution. The syntactic form you describe is called a compact constructor; it is a concise way of declaring the canonical constructor of a record, which is the constructor whose argument list matches that of the record. – Accede

It would be even better, if the Java Beans gets an update to recognize records, eliminating the need for the @ConstructorProperties annotation… – Hydroid

@BrianGoetz are you sure? I’ve read openjdk.java.net/contribute and get a different impression. For an outsider, it’ll take an hour to implement and weeks for trying to get it into the JDK… – Hydroid

@Hydroid The first few times will take longer, for sure. And yes, the non-code aspects can overshadow the code aspects -- and this is true for my job too. But that's just what "contribute" means at the scale of Java -- the code is only a small part of the work. (So yes, contributions are welcome, but "here's my code" is not the contribution most people think it is.) – Accede