TargetType with Enums only works when mapper method is static

[amithkumarg]

MapStruct version: 1.4.2.Final

Here is my sample code setup:

interface EnumMessage {
  boolean carrier(String message);

  String getValue();

  default String getMessage() {
    return getValue().toUpperCase();
  }
}

enum EnumMessageA implements EnumMessage {
  GREAT("You are doing great"),
  GOOD("You are doing good"),
  OK("You are doing ok");

  private String value;

  EnumMessageA(final String value) {
    this.value = value;
  }

  @Override
  public String getValue() {
    return value;
  }

  @Override
  public boolean carrier(final String message) {
    return this.value.equals(message);
  }
}

class SourceX {
  public String name;
  public String message;
}

class TargetX {
  public String name;
  public EnumMessageA messageA;
}

@Mapper
interface EnumMapper {
  EnumMapper INSTANCE = Mappers.getMapper(EnumMapper.class);

  @Mapping(source = "message", target = "messageA", qualifiedByName = "stringToEnum")
  TargetX toTarget(SourceX source);

  @Mapping(source = "messageA", target = "message", qualifiedByName = "enumToString")
  SourceX toSource(TargetX target);

  @Named("stringToEnum")
  default <T extends EnumMessage> T mapStringToEnum(
      final String message, @TargetType final Class<T> enumClass) {
    final T[] values = enumClass.getEnumConstants();
    return Arrays.stream(values)
        .filter(enumValue -> enumValue.carrier(message))
        .findFirst()
        .orElse(null);
  }

  @Named("enumToString")
  default <T extends EnumMessage> String mapEnumToString(final T enumValue) {
    return enumValue.getMessage();
  }
}

Here is the test class:

 public class EnumMapperTest {
    
      @Test
      void checkMapping() {
        TargetX target = new TargetX();
        target.name = "MapStructTesting";
        target.messageA = EnumMessageA.GREAT;
        Assertions.assertEquals(
            "You are doing great".toUpperCase(), EnumMapper.INSTANCE.toSource(target).message);
    
        SourceX source = new SourceX();
        source.name = "MapStructTesting";
        source.message = "You are doing ok";
        Assertions.assertEquals(EnumMessageA.OK, EnumMapper.INSTANCE.toTarget(source).messageA);
      }
}

I get this compilation error:

 error: Qualifier error. No method found annotated with @Named#value: [ stringToEnum ]. See https://mapstruct.org/faq/#qualifier for more info.
      @Mapping(source = "message", target = "messageA", qualifiedByName = "stringToEnum")
     error: Can't map property "String message" to "EnumMessageA messageA". Consider to declare/implement a mapping method: "EnumMessageA map(String value)".
      @Mapping(source = "message", target = "messageA", qualifiedByName = "stringToEnum")

I only way to get this working for MapStruct to use the customer mapper method for string to enum, is move the mapStringToEnum inside a helper class make it static, and pass the helper class in @Mapper uses attribute.

So my modified code should look like this to work:

@Mapper
public class EnumMapperHelper {

  @Named("stringToEnum")
  public static <T extends EnumMessage> T mapStringToEnum(
      final String message, @TargetType final Class<T> enumClass) {
    final T[] values = enumClass.getEnumConstants();
    return Arrays.stream(values)
        .filter(enumValue -> enumValue.carrier(message))
        .findFirst()
        .orElse(null);
  }

  @Named("enumToString")
  //this doesn't have to be static but yes the @Qualifier is required
  public static <T extends EnumMessage> String mapEnumToString(final T enumValue) {
    return enumValue.getMessage();
  }
}


@Mapper(uses = EnumMapperHelper.class) 
interface EnumMapper {
  EnumMapper INSTANCE = Mappers.getMapper(EnumMapper.class);

  @Mapping(source = "message", target = "messageA", qualifiedByName = "stringToEnum")
  TargetX toTarget(SourceX source);

  @Mapping(source = "messageA", target = "message", qualifiedByName = "enumToString")
  SourceX toSource(TargetX target);
}

[Zegveld]

Your original code works for me.

I've got the following imports:

import org.mapstruct.Mapper;
import org.mapstruct.Mapping;
import org.mapstruct.Named;
import org.mapstruct.TargetType;
import org.mapstruct.factory.Mappers;

I've seen that the Named annotation exists in multiple packages so it might be that you had the wrong import for the annotation.
Not org.mapstruct.Named but for example javax.inject.Named.

[amithkumarg]

Yes, you are right. I had the wrong import for Named annotation. Thanks for catching that.