https://www.cnblogs.com/qinwangchen/p/5418028.html

* Convert byte[] to hex string.這裏我們可以將byte轉換成int，然後利用Integer.toHexString(int)來轉換成16進制字符串。  
 * @param src byte[] data  
 * @return hex string  
 */     
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();  
}  
/** 
 * Convert hex string to byte[] 
 * @param hexString the hex string 
 * @return byte[] 
 */  
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;  
}  
/** 
 * Convert char to byte 
 * @param c char 
 * @return byte 
 */  
 private byte charToByte(char c) {  
    return (byte) "0123456789ABCDEF".indexOf(c);  
}

java中byte轉換int時為何與0xff進行與運算?看原著

Java中byte與16進制字符串的互相轉換