java按照GBK编码格式 字节定长截取字符串

    /**
     * 定长截取字符串 [按照字节长度截取]
     * @param origNal 需要截取的原字符串
     * @param start 截取起始下标
     * @param count 截取的总长度
     * @return 截取后的字符串
     */
    public String subStr(String origNal, int start, int count) {
        // 原字符串合理性校验
        if (origNal == null || "".equals(origNal)) {
            return origNal;
        }
        StringBuilder builder = new StringBuilder();
        int len = 0;
        char c;
        try {
            for (int i = 0; i < origNal.toCharArray().length; i++) {
                c = origNal.charAt(i);
                len += String.valueOf(c).getBytes("GBK").length;

                if (len >= start && len <= start + count) {
                    builder.append(c);
                }
                if (len > start + count) {
                    break;
                }
            }
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        }
        return new String(builder);
    }