Update (2021) – Java 17 now includes java.util.HexFormat
(only took 25 years):
HexFormat.of().parseHex(s)
For older versions of Java:
Here’s a solution that I think is better than any posted so far:
/* s must be an even-length string. */
public static byte[] hexStringToByteArray(String s) {
int len = s.length();
byte[] data = new byte[len / 2];
for (int i = 0; i < len; i += 2) {
data[i / 2] = (byte) ((Character.digit(s.charAt(i), 16) << 4)
+ Character.digit(s.charAt(i+1), 16));
}
return data;
}
Reasons why it is an improvement:
-
Safe with leading zeros (unlike BigInteger) and with negative byte values (unlike Byte.parseByte)
-
Doesn’t convert the String into a
char[]
, or create StringBuilder and String objects for every single byte. -
No library dependencies that may not be available
Feel free to add argument checking via assert
or exceptions if the argument is not known to be safe.