Convert a string representation of a hex dump to a byte array using Java

Question

I am looking for a way to convert a long string  from a dump   that represents hex values into a byte array   I couldn t have phrased it better than the person that posted the same question here   But to keep it original  I ll phrase it my own way  suppose I have a string  00A0BF  that I would like interpreted as the  byte    0x00 0xA0 0xBf    what should I do   I am a Java novice and ended up using BigInteger and watching out for leading hex zeros  But I think it is ugly and I am sure I am missing something simple

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I know this is a very old thread  but still like to add my penny worth   If I really need to code up a simple hex string to binary converter  I d like to do it as follows   public static byte   hexToBinary String s              skipped any input validation code          byte   data   new byte s length   2      for  int i 0  j 0          i lt s length    amp  amp  j lt data length          i  2  j             data j     byte Integer parseInt s substring i  i 2   16          return data

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One-liners   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       Warnings     in Java 9 Jigsaw this is no longer part of the  default  java se root set so it will result in a ClassNotFoundException unless you specify --add-modules java se ee  thanks to  eckes  Not available on Android  thanks to Fabian for noting that   but you can just take the source code if your system lacks javax xml for some reason  Thanks to  Bert Regelink for extracting the source

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Based on the op voted solution  the following should be a bit more efficient     public static byte    hexStringToByteArray  final String s        if  s    null     s length      2     1        throw new IllegalArgumentException         final char    chars   s toCharArray         final int len   chars length      final byte    data   new byte  len   2       for  int i   0  i  lt  len  i    2          data i   2     byte    Character digit  chars i   16   lt  lt  4    Character digit  chars i   1   16              return data        Because  the initial conversion to a char array spares the length checks in charAt

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The BigInteger   Method from java math is very Slow and not recommandable   Integer parseInt HEXString  16   can cause problems with some characters without converting to Digit   Integer  a Well Working method   Integer decode  0xXX    byteValue     Function   public static byte   HexStringToByteArray String s        byte data     new byte s length   2       for int i 0 i  lt  s length   i  2            data i 2     Integer decode  0x  s charAt i  s charAt i 1    byteValue              return data      Have Fun  Good Luck

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You can now use BaseEncoding in guava to accomplish this   BaseEncoding base16   decode string     To reverse it use   BaseEncoding base16   encode bytes

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public static byte   hex2ba String sHex  throws Hex2baException       if  1  sHex length   2            throw new Hex2baException  Hex string need even number of chars                byte   ba   new byte sHex length   2       for  int i 0 i lt sHex length   2 i              ba i     Integer decode                   0x  sHex substring i 2   i 1  2    byteValue              return ba

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I ve always used a method like  public static final byte   fromHexString final String s        String   v   s split           byte   arr   new byte v length       int i   0      for String val  v            arr i       Integer decode  0x    val  byteValue               return arr      this method splits on space delimited hex values but it wouldn t be hard to make it split the string on any other criteria such as into groupings of two characters

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The HexBinaryAdapter provides the ability to marshal and unmarshal between String and byte     import javax xml bind annotation adapters HexBinaryAdapter   public byte   hexToBytes String hexString         HexBinaryAdapter adapter   new HexBinaryAdapter         byte   bytes   adapter unmarshal hexString        return bytes      That s just an example I typed in   I actually just use it as is and don t need to make a separate method for using it

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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  lt  len  i    2            data i   2     byte    Character digit s charAt i   16   lt  lt  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

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I like the Character digit solution  but here is how I solved it  public byte   hex2ByteArray  String hexString         String hexVal    0123456789ABCDEF       byte   out   new byte hexString length     2        int n   hexString length         for  int i   0  i  lt  n  i    2               make a bit representation in an int of the hex value          int hn   hexVal indexOf  hexString charAt  i              int ln   hexVal indexOf  hexString charAt  i   1                 now just shift the high order nibble and add them together         out i 2     byte     hn  lt  lt  4     ln               return out

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In android  if you are working with hex  you can try okio   simple usage   byte   bytes   ByteString decodeHex  c000060000   toByteArray      and result will be    -64  0  6  0  0

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EDIT  as pointed out by  mmyers  this method doesn t work on input that contains substrings corresponding to bytes with the high bit set   80  -  FF    The explanation is at Bug ID  6259307 Byte parseByte not working as advertised in the SDK Documentation   public static final byte   fromHexString final String s        byte   arr   new byte s length   2       for   int start   0  start  lt  s length    start    2                 String thisByte   s substring start  start 2           arr start 2    Byte parseByte thisByte  16             return arr

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I think will do it for you  I cobbled it together from a similar function that returned the data as a string   private static byte   decode String encoded        byte result     new byte encoded 2       char enc     encoded toUpperCase   toCharArray        StringBuffer curr      for  int i   0  i  lt  enc length  i    2            curr   new StringBuffer              curr append String valueOf enc i             curr append String valueOf enc i   1             result i     byte  Integer parseInt curr toString    16             return result

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The Hex class in commons-codec should do that for you   http   commons apache org codec   import org apache commons codec binary Hex      byte   decoded   Hex decodeHex  00A0BF       0x00 0xA0 0xBF

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My formal solution          Decodes a hexadecimally encoded binary string      lt p gt     Note that this function does  lt em gt NOT lt  em gt  convert a hexadecimal number to a    binary number         param hex Hexadecimal representation of data      return The byte   representation of the given data      throws NumberFormatException If the hexadecimal input string is of odd    length or invalid hexadecimal string      public static byte   hex2bin String hex  throws NumberFormatException       if  hex length     2  gt  0            throw new NumberFormatException  Hexadecimal input string must have an even length               byte   r   new byte hex length     2       for  int i   hex length    i  gt  0             r i   2 - 1     byte   digit hex charAt --i      digit hex charAt --i    lt  lt  4              return r     private static int digit char ch        int r   Character digit ch  16       if  r  lt  0            throw new NumberFormatException  Invalid hexadecimal string      ch             return r      Is like the PHP hex2bin   Function but in Java style   Example   String data   new String hex2bin  6578616d706c65206865782064617461        data value   example hex data

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The Code presented by Bert Regelink simply does not work   Try the following   import javax xml bind DatatypeConverter  import java io     public class Test          Test     public void testObjectStreams    throws IOException  ClassNotFoundException                        ByteArrayOutputStream baos   new ByteArrayOutputStream                ObjectOutputStream oos   new ObjectOutputStream baos                String stringTest    TEST               oos writeObject  stringTest                 oos close                baos close                 byte   bytes   baos toByteArray                String hexString   DatatypeConverter printHexBinary  bytes               byte   reconvertedBytes   DatatypeConverter parseHexBinary hexString                assertArrayEquals  bytes  reconvertedBytes                 ByteArrayInputStream bais   new ByteArrayInputStream reconvertedBytes               ObjectInputStream ois   new ObjectInputStream bais                String readString    String  ois readObject                 assertEquals  stringTest  readString

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For Me this was the solution  HEX  FF01  then split to FF 255  and 01 01    private static byte   BytesEncode String encoded          System out println encoded length         byte result     new byte encoded length     2       char enc     encoded toUpperCase   toCharArray        String curr           for  int i   0  i  lt  encoded length    i i 2            curr   encoded substring i i 2           System out println curr           if i  0               result i    byte  Integer parseInt curr  16             else              result i 2    byte  Integer parseInt curr  16                         return result

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Late to the party  but I have amalgamated the answer above by DaveL into a class with the reverse action - just in case it helps    public final class HexString       private static final char   digits    0123456789ABCDEF  toCharArray         private HexString           public static final String fromBytes final byte   bytes            final StringBuilder buf   new StringBuilder            for  int i   0  i  lt  bytes length  i                  buf append HexString digits  bytes i   gt  gt  4   amp  0x0f                buf append HexString digits bytes i   amp  0x0f                      return buf toString               public static final byte   toByteArray final String hexString            if   hexString length     2     0                throw new IllegalArgumentException  Input string must contain an even number of characters                      final int len   hexString length            final byte   data   new byte len   2           for  int i   0  i  lt  len  i    2                data i   2     byte    Character digit hexString charAt i   16   lt  lt  4                        Character digit hexString charAt i   1   16                      return data            And JUnit test class   public class TestHexString         Test     public void test             String   tests     0FA1056D73        00    0123456789ABCDEF    FFFFFFFF             for  int i   0  i  lt  tests length  i                  String in   tests i               byte   bytes   HexString toByteArray in               String out   HexString fromBytes bytes               System out println in     DEBUG             System out println out     DEBUG             Assert assertEquals in  out

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Here is a method that actually works  based on several previous semi-correct answers    private static byte   fromHexString final String encoded        if   encoded length     2     0          throw new IllegalArgumentException  Input string must contain an even number of characters         final byte result     new byte encoded length   2       final char enc     encoded toCharArray        for  int i   0  i  lt  enc length  i    2            StringBuilder curr   new StringBuilder 2           curr append enc i   append enc i   1            result i 2     byte  Integer parseInt curr toString    16             return result      The only possible issue that I can see is if the input string is extremely long  calling toCharArray   makes a copy of the string s internal array   EDIT  Oh  and by the way  bytes are signed in Java  so your input string converts to  0  -96  -65  instead of  0  160  191   But you probably knew that already

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If you have a preference for Java 8 streams as your coding style then this can be achieved using just JDK primitives   String hex    0001027f80fdfeff    byte   converted   IntStream range 0  hex length     2       map i - gt  Character digit hex charAt i   2   16   lt  lt  4   Character digit hex charAt  i   2    1   16        collect ByteArrayOutputStream  new               ByteArrayOutputStream  write                s1  s2  - gt  s1 write s2 toByteArray    0  s2 size          toByteArray      The   0  s2 size   parameters in the collector concatenate function can be omitted if you don t mind catching IOException

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For what it s worth  here s another version which supports odd length strings  without resorting to string concatenation   public static byte   hexStringToByteArray String input        int len   input length         if  len    0            return new byte                  byte   data      int startIdx      if  len   2    0            data   new byte  len   2    1           data 0     byte  Character digit input charAt 0   16           startIdx   1        else           data   new byte len   2           startIdx   0             for  int i   startIdx  i  lt  len  i    2            data  i   1    2     byte    Character digit input charAt i   16   lt  lt  4                    Character digit input charAt i 1   16              return data

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One-liners   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        For those of you interested in the actual code behind the One-liners from FractalizeR  I needed that since javax xml bind is not available for Android  by default    this comes from com sun xml internal bind DatatypeConverterImpl java    public byte   parseHexBinary String s        final int len   s length             111  is not a valid hex encoding      if  len 2    0           throw new IllegalArgumentException  hexBinary needs to be even-length    s        byte   out   new byte len 2        for  int i 0  i lt len  i  2             int h   hexToBin s charAt i              int l   hexToBin s charAt i 1            if  h  -1    l  -1               throw new IllegalArgumentException  contains illegal character for hexBinary    s            out i 2     byte  h 16 l              return out     private static int hexToBin  char ch         if   0  lt  ch  amp  amp  ch lt   9       return ch- 0       if   A  lt  ch  amp  amp  ch lt   F       return ch- A  10      if   a  lt  ch  amp  amp  ch lt   f       return ch- a  10      return -1     private static final char   hexCode    0123456789ABCDEF  toCharArray     public String printHexBinary byte   data        StringBuilder r   new StringBuilder data length 2       for   byte b   data            r append hexCode  b  gt  gt  4   amp  0xF            r append hexCode  b  amp  0xF               return r toString

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I found Kernel Panic to have the solution most useful to me  but ran into problems if the hex string was an odd number   solved it this way   boolean isOdd int value        return  value  amp  0x01    0     private int hexToByte byte   out  int value        String hexVal    0123456789ABCDEF        String hexValL    0123456789abcdef       String st   Integer toHexString value       int len   st length        if  isOdd len                     len  1     need length to be an even number          st     0    st       make it an even number of chars               out 0   byte  len 2       for  int i  0 i lt len i  2                int hh   hexVal indexOf st charAt i                if  hh    -1   hh   hexValL indexOf st charAt i            int lh   hexVal indexOf st charAt i 1                if  lh    -1   lh   hexValL indexOf st charAt i 1            out  i 2  1     byte   hh  lt  lt  4  lh             return  len 2  1      I am adding a number of hex numbers to an array  so i pass the reference to the array I am using  and the int I need converted and returning the relative position of the next hex number   So the final byte array has  0  number of hex pairs   1     hex pairs  then the number of pairs

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Actually  I think the BigInteger is solution is very nice   new BigInteger  00A0BF   16  toByteArray      Edit  Not safe for leading zeros  as noted by the poster

[java] Convert a string representation of a hex dump to a byte array using Java?

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