public enum ExampleEnum {
    BLACK(100),
    BLUE(200),
    RED(300),
    GREEN(400);

    private final int code;

    private ExampleEnum(int code){
        this.code = code;
    }

    public int getCode() {
        return code; 
    }

    // the piece all the example code misses
    public static ExampleEnum fromCode(int code) {
        switch( code ) {
            case BLACK.code: {
                return BLACK;
            }
            case BLUE.code: {
                return BLUE;
            }
            case RED.code: {
                return RED;
            }
            case GREEN.code: {
                return GREEN;
            }
            default {
                ...
            }
        }
    }
}

@Converter( autoApply=true )
public class ExampleEnumConverter implements AttributeConverter<ExampleEnum,Integer> {
    @Override
    public Integer convertToDatabaseColumn(ExampleEnum value) {
        return value == null? null : value.getCode();
    }

    @Override
    public ExampleEnum convertToEntityAttribute(Integer value) {
        return value == null ? null : ExampleEnum.fromCode( value );
    }
}