How to convert hex string to Java string?

Question

For logging purpose we are converting the logs to byte array and then to hex string. I want to get it back in a Java String, but I am not able to do so.

The hex string in log file looks something like

fd00000aa8660b5b010006acdc0100000101000100010000

How can I decode this?

Reimeus · Answer 1 · 2015-08-28T11:56:21.147

74

Using Hex in Apache Commons:

String hexString = "fd00000aa8660b5b010006acdc0100000101000100010000";    
byte[] bytes = Hex.decodeHex(hexString.toCharArray());
System.out.println(new String(bytes, "UTF-8"));

edited Aug 28 '15 at 11:56

answered Dec 21 '12 at 13:30

Reimeus

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Hex is now part of Apache Commons Codec – DwB Aug 09 '18 at 21:32
3

Here the dependency: ``` commons-codec commons-codec 1.12 ``` – Jacques Koorts Jul 23 '19 at 13:17
It doesn’t need much to recognize, that this data is not a UTF-8 encoded string and `new String(bytes, "UTF-8")` will just produce garbage. – Holger Aug 27 '19 at 10:01
commons-codec commons-codec 1.10 – Harsh Sep 30 '22 at 22:30

telebog · Answer 2 · 2020-02-05T15:24:35.367

34

byte[] bytes = javax.xml.bind.DatatypeConverter.parseHexBinary(hexString);
String result= new String(bytes, encoding);

edited Feb 05 '20 at 15:24

answered Feb 19 '15 at 15:53

telebog

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Where the heck do I find `DatatypeConverter`? – zundi May 11 '17 at 03:26
Not public anymore in recent Java versions – Jean-Alexis Aufauvre Mar 27 '19 at 14:20
javax.xml.bind.DatatypeConverter – telebog Feb 05 '20 at 15:23
what are the encoding values? – gumuruh Nov 03 '20 at 10:34
https://docs.oracle.com/javase/7/docs/api/java/nio/charset/Charset.html – telebog Nov 19 '20 at 09:18

score 13 · Answer 3 · edited Sep 27 '20 at 16:10

13

You can go from String (hex) to byte array to String as UTF-8(?). Make sure your hex string does not have leading spaces and stuff.

public static byte[] hexStringToByteArray(String hex) {
    int l = hex.length();
    byte[] data = new byte[l / 2];
    for (int i = 0; i < l; i += 2) {
        data[i / 2] = (byte) ((Character.digit(hex.charAt(i), 16) << 4)
                + Character.digit(hex.charAt(i + 1), 16));
    }
    return data;
}

Usage:

String b = "0xfd00000aa8660b5b010006acdc0100000101000100010000";
byte[] bytes = hexStringToByteArray(b);
String st = new String(bytes, StandardCharsets.UTF_8);
System.out.println(st);

edited Sep 27 '20 at 16:10

catch23

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answered Apr 05 '16 at 04:35

Debosmit Ray

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how to do ot for versions below kitkat? – Kaveesh Kanwal Jan 03 '17 at 11:41
may I ask what is the purpose of converting it to String as UTF-8? – Nov 18 '19 at 06:50

Aleksander Gralak · Answer 4 · 2012-12-21T13:53:14.510

10

First of all read in the data, then convert it to byte array:

 byte b = Byte.parseByte(str, 16);

and then use String constructor:

new String(byte[] bytes)

or if the charset is not system default then:

new String(byte[] bytes, String charsetName)

edited Dec 21 '12 at 13:53

answered Dec 21 '12 at 13:21

Aleksander Gralak

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Of course, it may or may not work depending on encoding used by "some other guys". Maybe they used Latin-9. Or UTF-8. Or EUC-JP. Or maybe it was in Big-Endian. Who knows? – Joker_vD Dec 21 '12 at 13:24
That's why you should specify the encoding which was used by log strings before conversion to hex string. – Aleksander Gralak Dec 21 '12 at 13:25
1

use `Byte.parseByte(str, 16);` to parse a hexadecimal number. – gogognome Dec 21 '12 at 13:36
The String constructor expects a byte array and not just byte, I tried and it failed. – st__gen_server Feb 01 '16 at 12:59
@Callforeach yes it it exactly what I gave as en example, byte[] stands for array not single byte: new String(byte[] bytes) – Aleksander Gralak Feb 03 '16 at 08:46
I'm not following... where did you get the `bytes` byte array from? – zundi May 11 '17 at 03:28
1

@zundi in first line you parse only single byte. So you need to use a loop to get all the bytes and put them in array. Please look at Munene iUwej Julius answer. His method is doing just that – Aleksander Gralak May 11 '17 at 20:37

score 6 · Answer 5 · edited Feb 02 '15 at 06:21

6

Try the following code:

public static byte[] decode(String hex){

        String[] list=hex.split("(?<=\\G.{2})");
        ByteBuffer buffer= ByteBuffer.allocate(list.length);
        System.out.println(list.length);
        for(String str: list)
            buffer.put(Byte.parseByte(str,16));

        return buffer.array();

}

To convert to String just create a new String with the byte[] returned by the decode method.

edited Feb 02 '15 at 06:21

rink.attendant.6

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answered Feb 02 '15 at 06:16

Munene iUwej Julius

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I changed Byte.parseByte to (byte)Integer.parseInteger to allow for numbers > 128 to be parsed. – domenukk Dec 13 '15 at 16:45
@domenukk it's Integer.parseInt(..) not Integer.parseInteger(..) . Byte.parseByte implemented as follow { return (byte) Integer.parseInt(Str, base);} – Error Dec 13 '16 at 06:17
@Munene thanx 4 regex – Error Dec 13 '16 at 06:18

score 5 · Answer 6 · answered Apr 01 '16 at 13:35

5

Just another way to convert hex string to java string:

public static String unHex(String arg) {        

    String str = "";
    for(int i=0;i<arg.length();i+=2)
    {
        String s = arg.substring(i, (i + 2));
        int decimal = Integer.parseInt(s, 16);
        str = str + (char) decimal;
    }       
    return str;
}

answered Apr 01 '16 at 13:35

Kunal Surana

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Lots of substrings being created. Not ideal. – Jonathan Sep 02 '16 at 00:18
replace "String str" with a StringBuffer(), and use sb.append(char) if performance is an issue. – roninjoe Jan 23 '20 at 17:18

score 5 · Answer 7 · answered Mar 28 '22 at 18:21

There is yet another way to do this if using JDK17 or above, see the new HexFormat class which has useful methods for converting byte[] <=> hexadecimal String :

String hexStr ="5468697320697320616e206578616d706c6520737472696e67";
byte[] bytes = HexFormat.of().parseHex(hexStr);
String str = new String(bytes, StandardCharsets.UTF_8 /* or Charset.forName("whateverencoding")*/);

You of course need to know the exact character encoding of the hexadecimal representation in order to generate the correct String value.

How to convert hex string to Java string?

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