@Transient
private Duration myDuration;

@Column(name="DURATION")
String myDurationString;

@PostLoad
public void init() {
  this.myDuration = this.myDurationString == null ? null : Duration.parse(this.myDurationString);
};

public Duration getMyDuration() {
  return this.myDuration;
}

public void setMyDuration(Duration _myDuration) {
  this.myDurationString = _myDuration == null ? null : _myDuration.toString();
}

@Converter
public class DurationToStringConverter implements AttributeConverter<Duration, String>
{

    @Override
    public String convertToDatabaseColumn(Duration duration)
    {
        return duration == null ? null : duration.toString();
    }

    @Override
    public Duration convertToEntityAttribute(String dbData)
    {
        return dbData == null ? null : Duration.parse(dbData);
    }
}

@Entity
public class Ent {

    @Column
    @Convert(DurationToStringConverter.class)
    Duration duration;

}