Java Record with @Builder.Default

Question

I'm wondering is there any way to combine java record with lombok's @Builder.Default? Let's consider an example with properties object for new file creation.

Before java 14

@Value
@Builder
public class FileProperties {
    @Builder.Default
    String directory = System.getProperty("user.home");
    @Builder.Default
    String name = "New file";
    @Builder.Default
    String extension = ".txt";
}

Java 14

@Builder
public record FileProperties (
        String directory,
        String name,
        String extension
) {}

But in case if I try to use something like

@Builder
public record FileProperties (
        @Builder.Default
        String directory = System.getProperty("user.home")
) {}

Compiler will fail with an error, revealing that such syntax is not allowed. Do we have any solution to this problem?

Answer 1

You can achieve the same outcome not by @Builder.Default but by defining the builder itself with defaults for Lombok:

@Builder
public record FileProperties (
        String directory,
        String name,
        String extension
) {
    public static class FilePropertiesBuilder {
        FilePropertiesBuilder() {
            directory = System.getProperty("user.home");
            name = "New file";
            extension = ".txt";
        }
    }
}

Then to test it:

public static void main(String[] args) {
    System.out.println(FileProperties.builder().build());
}

Output:

FileProperties[directory=/home/me, name=New file, extension=.txt]

Answer 2

Don't use a record if you want to do more things than recording values in a container. In this case you shouldn't use a record because it doesn't allow you to instruct something different than simple recording your arguments.

If you want a default value for any instance you are creating of this class you need a "normal" constructor.

That's why you can't set values (again) in records.