常用字节转换（字符串转16进制，16进制转字符串）

private static byte charToByte(char c) {
        return (byte) "0123456789ABCDEF".indexOf(c);
    }
    public static String bytesToHexString(byte[] src){
        StringBuilder stringBuilder = new StringBuilder("");
        if (src == null || src.length <= 0) {
            return null;
        }
        for (int i = 0; i < src.length; i++) {
            int v = src[i] & 0xFF;
            String hv = Integer.toHexString(v);
            if (hv.length() < 2) {
                stringBuilder.append(0);
            }
            stringBuilder.append(hv);
        }
        return stringBuilder.toString();
    }
    public static byte[] hexStringToBytes(String hexString) {
        if (hexString == null || hexString.equals("")) {
            return null;
        }
        hexString = hexString.toUpperCase();
        int length = hexString.length() / 2;
        char[] hexChars = hexString.toCharArray();
        byte[] d = new byte[length];
        for (int i = 0; i < length; i++) {
            int pos = i * 2;
            d[i] = (byte) (charToByte(hexChars[pos]) << 4 | charToByte(hexChars[pos + 1]));
        }
        return d;
    }

/**
* hex格式char转二进制
*/
unsigned char hex_of_char(char c) {
  unsigned char tmp = 0;
  if(c >= '0' && c <= '9') {
    tmp = (c - '0');
  }
  else if(c >= 'A' && c <= 'F') {
    tmp = (c - 'A' + 10);
  }
  else if(c >= 'a' && c <= 'f') {
    tmp = (c - 'a' + 10);
  }
  return tmp;
}
static char g_hex_map_table[] = "0123456789ABCDEF";
/**
* 字节数组转hex格式字符串
* @param print_buf: 十六进制字符串buffer
* @param print_buf_len: 十六进制字符串buffer长度
* @param bytes: 二进制数据
* @param bytes_len: 二进制数据长度
*/
char* bytes_to_hex_string(
  char* print_buf, 
  int print_buf_len, 
  const unsigned char* bytes, 
  int len) {
  int i = 0;
  /**
  * 入参校验
  */ 
  if(print_buf == NULL || bytes == NULL || (len * 2 + 1) > print_buf_len) {
    return NULL;
  }
  for(i = 0; i < len; i++) {
    print_buf[i * 2] = g_hex_map_table[(bytes[i] >> 4) & 0x0F];
    print_buf[i * 2 + 1] = g_hex_map_table[(bytes[i]) & 0x0F];
  }
  /**
  * 填充字符串结束符
  */
  print_buf[i * 2] = '\0';
  /**
  * 返回目标地址
  */
  return print_buf;
}
/**
* hex格式字符串转字节数组
* @param hex_string: 十六进制字符串
* @param hex_string_len: 十六进制字符串长度
* @param bytes: 二进制数据存储空间
* @param bytes_len: 目标空间长度
*/
int hex_string_to_bytes(
  char* hex_string, 
  int hex_string_len, 
  unsigned char* bytes, 
  int bytes_len) {
  int i = 0;
  /**
  * 校验十六进制字符串长度必须偶数，并且目标存储空间必须足够存放转换后的二进制数据
  */
  if((hex_string_len % 2 != 0) || (bytes_len * 2 < hex_string_len)) {
    return -1;
  }
  for(i = 0; i < hex_string_len; i += 2) {
    bytes[i/2] = ((hex_of_char(hex_string[i]) << 4) & 0xF0) | 
          (hex_of_char(hex_string[i + 1]) & 0x0F);
  }
  return 1;
}