Trying to create a generic mapper in mapstruct for all the fields with target and source as String

Question

I have this requirement in which for all the String -> String mappings, I need to check if the source string is empty and if it is I want to return null. I thought this would work but unfortunately doesn't

@Mapping(source = "in", target = ".", qualifiedByName = "stringConverter")
abstract String mapString(String in);

I thought this would generate a function like

String mapString(String in) {
    if ( in == null ) {
        return null;
    }

    String string = stringConverter(in);

    return string;
}

Or something similar. Here stringConverter just basically checks if the string is empty and returns null if so, else the original string. But in turn what I actually get is

String mapString(String in) {
    if ( in == null ) {
        return null;
    }

    String string = new String();

    return string;
}

Is it possible to create a generic function that handles mappings for all the string fields when using mapstruct?

Answer 1

MapStruct is meant for mapping beans and not for mapping between Strings.

You need to write a custom method for mapping between String and MapStruct will use that method.

public class StringConverter {

    public static String map(String value) {
        return (value == null || value.isEmpty()) ? null : value;
    }

}