import org.springframework.core.convert.converter.Converter;
import org.springframework.stereotype.Component;

@Component
public class FlexibleDateTimeConverter implements Converter<String, String> {

@Override
public String convert(String source) {
    if (source == null || source.trim().isEmpty()) return null;
    String text = source.trim();
    if (text.matches("^\\d{4}-\\d{2}$")) {
        text += "-01 00:00:00";
    } else if (text.matches("^\\d{4}-\\d{2}-\\d{2}$")) {
        text += " 00:00:00";
    } else if (text.matches("^\\d{4}-\\d{2}-\\d{2} \\d{2}$")) {
        text += ":00:00";
    } else if (text.matches("^\\d{4}-\\d{2}-\\d{2} \\d{2}:\\d{2}$")) {
        text += ":00";
    }
    return text;
}

}