How to abstract method call in lambda expression?

Question

Given the following two methods (not compilable code, just the structure):

  protected String mapABC(
    Entity entity, @Context MappingContext mappingContext) {
    return Optional.ofNullable(getSomething(entity))
      .map(
        x ->  getBlah(x::getName))
      .orElse(null);
  }

  protected String mapXYZ(
    Entity entity, @Context MappingContext mappingContext) {
    return Optional.ofNullable(getSomething(entity))
      .map(
        x ->  getBlah(x::getFirstName))
      .orElse(null);
  }

I am thinking about how it would look when the duplicate logic is avoided, so that one could write something like this structure:

protected String mapXYZ(
    Entity entity, @Context MappingContext mappingContext) {
    return xxx(getName());
  }

  protected String mapXYZ(
    Entity entity, @Context MappingContext mappingContext) {
    return xxx(getFirsName());
  }


  private String xxx(Methodreference m){
    return Optional.ofNullable(getSomething(entity))
      .map(
        x ->  getBlah(x::m))
      .orElse(null);
  }

Type of x is:

@AllArgsConstructor
@NoArgsConstructor
@Data
@Builder(toBuilder = true)
public class DetailData {
  private String name;
  private String firstname;
}

Any ideas I could try?

Answer 1

You should take a Function<DetailData, String>

private String map(Function<DetailData, String> m){
    return Optional.ofNullable(getSomething(entity))
        .map(
            x -> getBlah(m.apply(x)))
        .orElse(null);
}

Usage:

protected String mapXYZ(
    Entity entity, @Context MappingContext mappingContext) {
    return map(DetailData::getName);
}

protected String mapXYZ(
    Entity entity, @Context MappingContext mappingContext) {
    return map(DetailData::getFirstName);
}