goja-core/src/main/java/goja/core/kits/IdCardKit.java
public static String getBirthByIdCard(String idCard) {
        Integer len = idCard.length();
        if (len < CHINA_ID_MIN_LENGTH) {
            return null;
        } else if (len == CHINA_ID_MIN_LENGTH) {
            idCard = conver15CardTo18(idCard);
        }
        return idCard.substring(6, 14);
    }
public static String getBirthByIdCard(String idCard) {
        Integer len = idCard.length();
        if (len < CHINA_ID_MIN_LENGTH) {
            return null;
        } else if (len == CHINA_ID_MIN_LENGTH) {
            idCard = conver15CardTo18(idCard);
        }
        return idCard.substring(6, 14);
    }
根据身份编号获取生日

@param idCard 身份编号
@return 生日(yyyyMMdd)