In Java, how do I convert a hex string to a byte[]?

Question

I am using the below function in Java to convert an encrypted String into hex format:

public static String toHex(byte [] buf) {
    StringBuffer strbuf = new StringBuffer(buf.length * 2);
    int i;
    for (i = 0; i < buf.length; i++) {
        if (((int) buf[i] & 0xff) < 0x10) {
            strbuf.append("0");
        }
        strbuf.append(Long.toString((int) buf[i] & 0xff, 16));
    }
    return strbuf.toString();
}

Now I want to convert that hex string back into a byte array. How can I do that?

For example,

(1) Plain Text = 123
(2) Encrypted Text = «h>kq*«¬Mí“~èåZ  \}?
(3) Encrypted Text in Hex = f263575e7b00a977a8e9a37e08b9c215feb9bfb2f992b2b8f11e

I can go from (2) to (3), but how do I go from (3) back to (2)?

aa to Ra. One Movie no kamal chhe. you can join me in my chat room http://chat.stackoverflow.com/rooms/6137/ — Lucifer, Jan 17 '12 at 05:47
What's a Back byte array? Is that different from a byte array? — Keith Irwin, Jan 17 '12 at 06:00
How to convert binary/byte string into hex? http://stackoverflow.com/questions/29603046/decrypt-string-in-java-which-was-encrypted-using-symmetric-key-in-php/29603246?noredirect=1#29603046 — Scorpion, Apr 13 '15 at 11:29

score 113 · Answer 1 · edited May 23 '17 at 12:26

113

The accepted answer does not consider leading zeros which may cause problems

This question answers it. Depending on whether you want to see how its done or just use a java built-in method. Here are the solutions copied from this and this answers respectively from the SO question mentioned.

Option 1: Util method

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;
}

Option 2: One-liner build-in

import javax.xml.bind.DatatypeConverter;

public static String toHexString(byte[] array) {
    return DatatypeConverter.printHexBinary(array);
}

public static byte[] toByteArray(String s) {
    return DatatypeConverter.parseHexBinary(s);
}

edited May 23 '17 at 12:26

Community

1
1

answered Oct 01 '13 at 14:54

dARKpRINCE

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your answer help me with http://stackoverflow.com/a/25790612/173149, thanks +1 – gavenkoa Sep 11 '14 at 14:56
+1 for the one-liner option using classes already provided with Java. – Zeimyth Oct 21 '14 at 17:47
For the string `56276BE1`, it gives me bytes of `86, 39, 107, -31`. But an other application written in C# gives me `86, 39, 107, 225` for the same hex string. Which one is true? – Fer Jun 26 '15 at 08:47
Both are correct. C# handles bytes differently than Java. In Java byte value is between -127 and 127, while C# has 0 to 255. – dARKpRINCE Jun 26 '15 at 12:19
4

The one-liner built-in seems to be not-so-built-in anymore on Java 9 though, as simply importing `javax.xml.bind.DatatypeConverter` does not work. – ionizer Dec 08 '17 at 18:25
1

as of Java 17 there is now an officially provided method `java.util.HexFormat.of().parseHex(s)` – Dave L. Dec 13 '21 at 20:54

score 47 · Accepted Answer · answered Jan 17 '12 at 05:58

47

 String s="f263575e7b00a977a8e9a37e08b9c215feb9bfb2f992b2b8f11e";
 byte[] b = new BigInteger(s,16).toByteArray();

answered Jan 17 '12 at 05:58

Kushan

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This did not give me the result I was looking for, but the simple one-liner method in dARKpRINCE's response did. – Jeremy Goodell Apr 07 '15 at 21:41
`cs.setBytes(1,new BigInteger(regReportId,16).toByteArray());` this worked when i have to pass RAW datatype to Oracle sproc – Dilip Oct 06 '16 at 16:12
The `new BigInteger(s,16).toByteArray();` is not correct. I input a 34-length hex string, and output a 18-length bytes. What I want is a 17-length bytes – Ninja Aug 11 '17 at 11:02
I think this gives wrong result sometimes. for instance, it gives 17 bytes for A85565ED63B893F5A3EF85D88819D484. but it should be 16 bytes – Adem Sep 06 '17 at 21:00
this gives the wrong results; DarkPrince "util method" works correctly for me. – Blisterpeanuts Mar 03 '21 at 18:54

score 6 · Answer 3 · edited Jan 12 '16 at 20:36

6

I found that the DatatypeConverter.parseHexBinary is more costly (two times) than:

org.apache.commons.codec.binary.Hex(str.toCharArray())

edited Jan 12 '16 at 20:36

Peter Mortensen

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answered Oct 28 '15 at 22:29

Rony Joy

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This is more costly than DatatypeConverter, since Apache commons is an additional library (dependency, size, etc) - while DatatypeConverter is part of the JDK. – foo Jun 13 '19 at 16:39

In Java, how do I convert a hex string to a byte[]?

3 Answers3

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