How to convert a byte array to a hex string in Java

Question

I have a byte array filled with hex numbers and printing it the easy way is pretty pointless because there are many unprintable elements  What I need is the exact hexcode in the form of  3a5f771c

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If you re using the Spring Security framework  you can use   import org springframework security crypto codec Hex  final String testString    Test String   final byte   byteArray   testString getBytes    System out println Hex encode byteArray

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Here are some common options ordered from simple  one-liner  to complex  huge library   If you are interested in performance  see the micro benchmarks below  Option 1  Code snippet - Simple  only using JDK Android  Option 1a  BigInteger One very simple solution is to use the BigInteger s hex representation  new BigInteger 1  someByteArray  toString 16    Note that since this handles numbers not arbitrary byte-strings it will omit leading zeros - this may or may not be what you want  e g  000AE3 vs 0AE3 for a 3 byte input   This is also very slow  about 100x slower compared to option 2  Option 1b  String format   Using the  X placeholder  String format   is able to encode most primitive types  short  int  long  to hex  String format  quot  X quot   ByteBuffer wrap eightByteArray  getLong      Option 1c  Integer Long  only 4 8 Byte Arrays  If you exclusively have 4 bytes arrays you can use the toHexString method of the Integer class  Integer toHexString ByteBuffer wrap fourByteArray  getInt      The same works with 8 byte arrays and Long Long toHexString ByteBuffer wrap eightByteArray  getLong      Option 2  Code snippet - Advanced Here is a full featured  copy  amp  pasteable code snippet supporting upper lowercase and endianness  It is optimized to minimize memory complexity and maximize performance and should be compatible with all modern Java versions  5    private static final char   LOOKUP TABLE LOWER   new char   0x30  0x31  0x32  0x33  0x34  0x35  0x36  0x37  0x38  0x39  0x61  0x62  0x63  0x64  0x65  0x66   private static final char   LOOKUP TABLE UPPER   new char   0x30  0x31  0x32  0x33  0x34  0x35  0x36  0x37  0x38  0x39  0x41  0x42  0x43  0x44  0x45  0x46            public static String encode byte   byteArray  boolean upperCase  ByteOrder byteOrder            our output size will be exactly 2x byte-array length     final char   buffer   new char byteArray length   2           choose lower or uppercase lookup table     final char   lookup   upperCase   LOOKUP TABLE UPPER   LOOKUP TABLE LOWER       int index      for  int i   0  i  lt  byteArray length  i                 for little endian we count from last to first         index    byteOrder    ByteOrder BIG ENDIAN    i   byteArray length - i - 1                      extract the upper 4 bit and look up char  0-A          buffer i  lt  lt  1    lookup  byteArray index   gt  gt  4   amp  0xF              extract the lower 4 bit and look up char  0-A          buffer  i  lt  lt  1    1    lookup  byteArray index   amp  0xF              return new String buffer      public static String encode byte   byteArray        return encode byteArray  false  ByteOrder BIG ENDIAN      The full source code with Apache v2 license and decoder can be found here  Option 3  Using a small optimized library  bytes-java While working on my previous project  I created this little toolkit for working with bytes in Java  It has no external dependencies and is compatible with Java 7   It includes  among others  a very fast and well tested HEX en decoder  import at favre lib bytes Bytes      Bytes wrap someByteArray  encodeHex    You can check it out on Github  bytes-java  Option 4  Apache Commons Codec Of course there is the good  ol commons codecs   warning opinion ahead  While working on the project outlined above I analyzed the code and was quite disappointed  a lot of duplicate unorganized code  obsolete and exotic codecs probably only useful for very few and quite over engineered and slow implementations of popular codecs  specifically Base64   I therefore would make an informed decision if you want to use it or an alternative  Anyways  if you still want to use it  here is a code snippet  import org apache commons codec binary Hex      Hex encodeHexString someByteArray     Option 5  Google Guava More often than not you already have Guava as a dependency  If so just use  import com google common io BaseEncoding      BaseEncoding base16   lowerCase   encode someByteArray    Option 6  Spring Security If you use the Spring framework with Spring Security you can use the following  import org springframework security crypto codec Hex     new String Hex encode someByteArray     Option 7  Bouncy Castle If you already use the security framework Bouncy Castle you can use its Hex util  import org bouncycastle util encoders Hex      Hex toHexString someByteArray    Not Really Option 8  Java 9  Compatibility or  Do Not Use JAXBs javax xml bind DatatypeConverter  In previous Java  8 and below  versions the Java code for JAXB was included as runtime dependency  Since Java 9 and Jigsaw modularisation your code cannot access other code outside of it s module without explicit declaration  So be aware if you get an exception like  java lang NoClassDefFoundError  javax xml bind JAXBException  when running on a JVM with Java 9   If so then switch implementations to any of the alternatives above  See also this question   Micro Benchmarks Here are results from a simple JMH micro benchmark encoding byte arrays of different sizes  The values are operations per second  so higher is better  Note that micro benchmarks very often do not represent real world behavior  so take these results with a grain of salt    Name  ops s               16 byte      32 byte    128 byte   0 95 MB    ---------------------- -----------  -----------  ----------  --------     Opt1  BigInteger        2 088 514    1 008 357     133 665         4     Opt2 3  Bytes Lib      20 423 170   16 049 841   6 685 522       825     Opt4  Apache Commons   17 503 857   12 382 018   4 319 898       529     Opt5  Guava            10 177 925    6 937 833   2 094 658       257     Opt6  Spring           18 704 986   13 643 374   4 904 805       601     Opt7  BC                7 501 666    3 674 422   1 077 236       152     Opt8  JAX-B            13 497 736    8 312 834   2 590 940       346    Specs  JDK 8u202  i7-7700K  Win10  24GB Ram  See the full benchmark here

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If you re looking for a byte array exactly like this for python  I have converted this Java implementation into python   class ByteArray    classmethod def char cls  args          cls hexArray    0123456789ABCDEF  encode  utf-16       j   0     length    cls hexArray       if j  lt  length          v   j  amp  0xFF         hexChars    None  None          hexChars j   2    str  cls hexArray    str v          hexChars j   2   1    str cls hexArray    str v    str 0x0F            Use if you want             hexChars pop        return str hexChars   array   ByteArray   print array char args

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Adding a utility jar for simple function is not good option  Instead assemble your own utility classes  following is possible faster implementation   public class ByteHex        public static int hexToByte 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 String   byteToHexTable   new String                  00    01    02    03    04    05    06    07    08    09    0A    0B    0C    0D    0E    0F            10    11    12    13    14    15    16    17    18    19    1A    1B    1C    1D    1E    1F            20    21    22    23    24    25    26    27    28    29    2A    2B    2C    2D    2E    2F            30    31    32    33    34    35    36    37    38    39    3A    3B    3C    3D    3E    3F            40    41    42    43    44    45    46    47    48    49    4A    4B    4C    4D    4E    4F            50    51    52    53    54    55    56    57    58    59    5A    5B    5C    5D    5E    5F            60    61    62    63    64    65    66    67    68    69    6A    6B    6C    6D    6E    6F            70    71    72    73    74    75    76    77    78    79    7A    7B    7C    7D    7E    7F            80    81    82    83    84    85    86    87    88    89    8A    8B    8C    8D    8E    8F            90    91    92    93    94    95    96    97    98    99    9A    9B    9C    9D    9E    9F            A0    A1    A2    A3    A4    A5    A6    A7    A8    A9    AA    AB    AC    AD    AE    AF            B0    B1    B2    B3    B4    B5    B6    B7    B8    B9    BA    BB    BC    BD    BE    BF            C0    C1    C2    C3    C4    C5    C6    C7    C8    C9    CA    CB    CC    CD    CE    CF            D0    D1    D2    D3    D4    D5    D6    D7    D8    D9    DA    DB    DC    DD    DE    DF            E0    E1    E2    E3    E4    E5    E6    E7    E8    E9    EA    EB    EC    ED    EE    EF            F0    F1    F2    F3    F4    F5    F6    F7    F8    F9    FA    FB    FC    FD    FE    FF              private static final String   byteToHexTableLowerCase   new String                  00    01    02    03    04    05    06    07    08    09    0a    0b    0c    0d    0e    0f            10    11    12    13    14    15    16    17    18    19    1a    1b    1c    1d    1e    1f            20    21    22    23    24    25    26    27    28    29    2a    2b    2c    2d    2e    2f            30    31    32    33    34    35    36    37    38    39    3a    3b    3c    3d    3e    3f            40    41    42    43    44    45    46    47    48    49    4a    4b    4c    4d    4e    4f            50    51    52    53    54    55    56    57    58    59    5a    5b    5c    5d    5e    5f            60    61    62    63    64    65    66    67    68    69    6a    6b    6c    6d    6e    6f            70    71    72    73    74    75    76    77    78    79    7a    7b    7c    7d    7e    7f            80    81    82    83    84    85    86    87    88    89    8a    8b    8c    8d    8e    8f            90    91    92    93    94    95    96    97    98    99    9a    9b    9c    9d    9e    9f            a0    a1    a2    a3    a4    a5    a6    a7    a8    a9    aa    ab    ac    ad    ae    af            b0    b1    b2    b3    b4    b5    b6    b7    b8    b9    ba    bb    bc    bd    be    bf            c0    c1    c2    c3    c4    c5    c6    c7    c8    c9    ca    cb    cc    cd    ce    cf            d0    d1    d2    d3    d4    d5    d6    d7    d8    d9    da    db    dc    dd    de    df            e0    e1    e2    e3    e4    e5    e6    e7    e8    e9    ea    eb    ec    ed    ee    ef            f0    f1    f2    f3    f4    f5    f6    f7    f8    f9    fa    fb    fc    fd    fe    ff              public static String byteToHex byte b           return byteToHexTable b  amp  0xFF              public static String byteToHex byte   bytes           if bytes    null  return null          StringBuilder sb   new StringBuilder bytes length 2           for byte b   bytes  sb append byteToHexTable b  amp  0xFF            return sb toString               public static String byteToHex short   bytes           StringBuilder sb   new StringBuilder bytes length 2           for short b   bytes  sb append byteToHexTable   byte b   amp  0xFF            return sb toString               public static String byteToHexLowerCase byte   bytes           StringBuilder sb   new StringBuilder bytes length 2           for byte b   bytes  sb append byteToHexTableLowerCase b  amp  0xFF            return sb toString               public static byte   hexToByte String hexString            if hexString    null  return null          byte   byteArray   new byte hexString length     2           for  int i   0  i  lt  hexString length    i    2                byteArray i   2     byte   hexToByte hexString charAt i     16   hexToByte hexString charAt i 1                       return byteArray             public static byte hexPairToByte char ch1  char ch2            return  byte   hexToByte ch1    16   hexToByte ch2

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At the minor cost of storing the lookup table this implementation is simple and very fast    private static final char   BYTE2HEX        000102030405060708090A0B0C0D0E0F        101112131415161718191A1B1C1D1E1F        202122232425262728292A2B2C2D2E2F        303132333435363738393A3B3C3D3E3F        404142434445464748494A4B4C4D4E4F        505152535455565758595A5B5C5D5E5F        606162636465666768696A6B6C6D6E6F        707172737475767778797A7B7C7D7E7F        808182838485868788898A8B8C8D8E8F        909192939495969798999A9B9C9D9E9F        A0A1A2A3A4A5A6A7A8A9AAABACADAEAF        B0B1B2B3B4B5B6B7B8B9BABBBCBDBEBF        C0C1C2C3C4C5C6C7C8C9CACBCCCDCECF        D0D1D2D3D4D5D6D7D8D9DADBDCDDDEDF        E0E1E2E3E4E5E6E7E8E9EAEBECEDEEEF        F0F1F2F3F4F5F6F7F8F9FAFBFCFDFEFF   toCharArray             public static String getHexString byte   bytes        final int len bytes length      final char   chars new char len lt  lt 1       int hexIndex      int idx 0      int ofs 0      while  ofs lt len          hexIndex  bytes ofs     amp  0xFF  lt  lt 1        chars idx    BYTE2HEX hexIndex           chars idx    BYTE2HEX hexIndex             return new String chars

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Here is a java util Base64-like implementation  isn t it pretty  import java util Arrays   public class Base16   a k a  Hex          public static class Encoder          private static char   toLowerHex   0   1   2   3   4   5   6   7   8   9   a   b   c   d   e   f            private static char   toUpperHex   0   1   2   3   4   5   6   7   8   9   A   B   C   D   E   F            private boolean upper          public Encoder boolean upper                this upper upper                    public String encode byte   data               char   value new char data length 2               char   toHex upper toUpperHex toLowerHex              for int i 0 j 0  i lt data length  i                     int octet data i  amp 0xFF                  value j    toHex octet gt  gt 4                   value j    toHex octet amp 0xF                             return new String value                     static final Encoder LOWER CASE new Encoder false           static final Encoder UPPER CASE new Encoder true             public static Encoder getEncoder            return Encoder LOWER CASE            public static Encoder getUpperEncoder            return Encoder UPPER CASE             public static class Decoder        private static int maxIndex 102        private static int   toIndex        static           toIndex new int maxIndex 1           Arrays fill toIndex  -1           char   chars   0   1   2   3   4   5   6   7   8   9   A   B   C   D   E   F   a   b   c   d   e   f            for int i 0  i lt chars length  i                toIndex  int chars i   i                          public Decoder                   public byte   decode String str              char   value str toCharArray              int start 0            if value length gt 2  amp  amp  value 0    0   amp  amp   value 1    x     value 1    X                  start 2                        int byteLength  value length-start  2     ignore trailing odd char if exists           byte   data new byte byteLength             for int i start j 0 i lt value length i  2 j                   int i1                int i2                char c1 value i                 char c2 value i 1                 if c1 gt maxIndex     i1 toIndex  int c1   lt 0    c2 gt maxIndex     i2 toIndex  int c2   lt 0                    throw new IllegalArgumentException  quot Invalid character at  quot  i                                 data j   byte   i1 lt  lt 4  i2                         return data                static final Decoder IGNORE CASE new Decoder          public static Decoder getDecoder          return Decoder IGNORE CASE

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A small variant of the solution proposed by  maybewecouldstealavan  which lets you visually bundle N bytes together in the output hex string    final static char   HEX ARRAY    0123456789ABCDEF  toCharArray     final static char BUNDLE SEP         public static String bytesToHexString byte   bytes  int bundleSize    bytes                char   hexChars   new char  bytes length   2     bytes length   bundleSize            for  int j   0  k   1  j  lt  bytes length  j    k                      int v   bytes j   amp  0xFF                  int start    j   2    j bundleSize                   hexChars start    HEX ARRAY v  gt  gt  gt  4                   hexChars start   1    HEX ARRAY v  amp  0x0F                    if   k   bundleSize     0                            hexChars start   2    BUNDLE SEP                                            return new String hexChars  trim            That is   bytesToHexString    DOOM    toCharArray   getBytes    2   2E2E 444F 4F4D 2E2E  bytesToHexString    DOOM    toCharArray   getBytes    4   2E2E444F 4F4D2E2E

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Can t find any solution on this page that doesn t   Use a loop Use javax xml bind DatatypeConverter which compiles fine but often throws java lang NoClassDefFoundError at runtime    Here s a solution which doesn t have the flaws above no promises mine doesn t have other flaws though   import java math BigInteger   import static java lang System out  public final class App2            proposed solution      public static String encode byte   bytes                      final int length   bytes length                BigInteger constructor throws if it is given an empty array          if  length    0                return  00                      final int evenLength    int  2   Math ceil length   2 0            final String format     0    evenLength    x                    final String result   String format  format  new BigInteger bytes             return result             public static void main String   args  throws Exception              00         out println encode new byte                      01         out println encode new byte    1                 203040         out println encode new byte    0x20  0x30  0x40                  416c6c20796f75722062617365206172652062656c6f6e6720746f2075732e         out println encode  All your base are belong to us   getBytes                   I couldn t get this under 62 opcodes  but if you can live without 0 padding in case the first byte is less than 0x10  then the following solution only uses 23 opcodes  Really shows how  easy to implement yourself  solutions like  pad with a zero if string length is odd  can get pretty expensive if a native implementation is not already available or in this case  if BigInteger had an option to prefix with zeros in toString    public static String encode byte   bytes                  final int length   bytes length            BigInteger constructor throws if it is given an empty array      if  length    0            return  00              return new BigInteger bytes  toString 16

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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

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My solution is based on maybeWeCouldStealAVan s solution  but does not rely on any additionaly allocated lookup tables  It does not uses any  int-to-char  casts hacks  actually  Character forDigit   does it  performing some comparison to check what the digit truly is  and thus might be a bit slower  Please feel free to use it wherever you want  Cheers   public static String bytesToHex final byte   bytes        final int numBytes   bytes length      final char   container   new char numBytes   2        for  int i   0  i  lt  numBytes  i                  final int b   bytes i   amp  0xFF           container i   2    Character forDigit b  gt  gt  gt  4  0x10           container i   2   1    Character forDigit b  amp  0xF  0x10              return new String container

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Converts bytes data to hex characters   param bytes byte array to be converted to hex string  return byte String in hex format  private static String bytesToHex byte   bytes        char   hexChars   new char bytes length   2       int v      for  int j   0  j  lt  bytes length  j              v   bytes j   amp  0xFF          hexChars j   2    HEX ARRAY v  gt  gt  gt  4           hexChars j   2   1    HEX ARRAY v  amp  0x0F             return new String hexChars

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I found three different ways here  http   www rgagnon com javadetails java-0596 html  The most elegant one  as he also notes  I think is this one   static final String HEXES    0123456789ABCDEF   public static String getHex  byte    raw         if   raw    null             return null            final StringBuilder hex   new StringBuilder  2   raw length        for   final byte b   raw             hex append HEXES charAt  b  amp  0xF0   gt  gt  4                append HEXES charAt  b  amp  0x0F               return hex toString

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The method javax xml bind DatatypeConverter printHexBinary    part of the Java Architecture for XML Binding  JAXB   was a convenient way to convert a byte   to a hex string  The DatatypeConverter class also included many other useful data-manipulation methods   In Java 8 and earlier  JAXB was part of the Java standard library  It was deprecated with Java 9 and removed with Java 11  as part of an effort to move all Java EE packages into their own libraries  It s a long story  Now  javax xml bind doesn t exist  and if you want to use JAXB  which contains DatatypeConverter  you ll need to install the JAXB API and JAXB Runtime from Maven   Example usage   byte bytes       byte 0   byte 0   byte 134   byte 0   byte 61   String hex   javax xml bind DatatypeConverter printHexBinary bytes     Will result in   000086003D   This answer the same as this one

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I usually use the following method for debuf statement  but i don t know if it is the best way of doing it or not  private static String digits    0123456789abcdef    public static String toHex byte   data       StringBuffer buf   new StringBuffer        for  int i   0  i    data length  i                  int v   data i   amp  0xff          buf append digits charAt v  gt  gt  4            buf append digits charAt v  amp  0xf              return buf toString

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How about this       String byteToHex final byte   hash                Formatter formatter   new Formatter            for  byte b   hash                        formatter format   02x   b                     String result   formatter toString            formatter close            return result

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The Apache Commons Codec library has a Hex class for doing just this type of work   import org apache commons codec binary Hex   String foo    I am a string   byte   bytes   foo getBytes    System out println  Hex encodeHexString  bytes

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I prefer to use this   final protected static char   hexArray    0123456789ABCDEF  toCharArray    public static String bytesToHex byte   bytes  int offset  int count        char   hexChars   new char count   2       for   int j   0  j  lt  count  j               int v   bytes j offset   amp  0xFF          hexChars j   2    hexArray v  gt  gt  gt  4           hexChars j   2   1    hexArray v  amp  0x0F             return new String hexChars       It is slightly more flexible adaptation of the accepted answer  Personally  I keep both the accepted answer and this overload along with it  usable in more contexts

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Shifting bytes is more efficient    You can use this one too   public static String getHexString  String s         byte   buf   s getBytes         StringBuffer sb   new StringBuffer         for  byte b buf                sb append String format   x   b                    return sb toString

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From the discussion here  and especially this answer  this is the function I currently use  private static final char   HEX ARRAY    quot 0123456789ABCDEF quot  toCharArray    public static String bytesToHex byte   bytes        char   hexChars   new char bytes length   2       for  int j   0  j  lt  bytes length  j              int v   bytes j   amp  0xFF          hexChars j   2    HEX ARRAY v  gt  gt  gt  4           hexChars j   2   1    HEX ARRAY v  amp  0x0F             return new String hexChars      My own tiny benchmarks  a million bytes a thousand times  256 bytes 10 million times  showed it to be much faster than any other alternative  about half the time on long arrays   Compared to the answer I took it from  switching to bitwise ops --- as suggested in the discussion --- cut about 20  off of the time for long arrays   Edit  When I say it s faster than the alternatives  I mean the alternative code offered in the discussions  Performance is equivalent to Commons Codec  which uses very similar code   2k20 version  with respect to Java 9 compact strings  private static final byte   HEX ARRAY    quot 0123456789ABCDEF quot  getBytes StandardCharsets US ASCII   public static String bytesToHex byte   bytes        byte   hexChars   new byte bytes length   2       for  int j   0  j  lt  bytes length  j              int v   bytes j   amp  0xFF          hexChars j   2    HEX ARRAY v  gt  gt  gt  4           hexChars j   2   1    HEX ARRAY v  amp  0x0F             return new String hexChars  StandardCharsets UTF 8

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This simple oneliner works for me     String result   new BigInteger 1  inputBytes  toString 16     EDIT - Using this will remove the leading zeros  but hey worked for my use-case  Thanks  Voicu for pointing it out

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I would use something like this for fixed length  like hashes   md5sum   String format   032x   new BigInteger 1  md digest

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Use DataTypeConverter classjavax xml bind DataTypeConverter  String hexString   DatatypeConverter printHexBinary bytes   raw

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Here s yet another method using Streams  private static String toHexString byte   bytes        return IntStream range 0  bytes length       mapToObj i - gt  String format  quot  02X quot   bytes i         collect Collectors joining

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private static String bytesToHexString byte   bytes  int length            if  bytes    null    length    0  return null           StringBuilder ret   new StringBuilder 2 length            for  int i   0   i  lt  length   i                  int b               b   0x0f  amp   bytes i   gt  gt  4               ret append  0123456789abcdef  charAt b                 b   0x0f  amp  bytes i               ret append  0123456789abcdef  charAt b                       return ret toString

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A Guava solution  for completeness   import com google common io BaseEncoding      byte   bytes    Hello world  getBytes StandardCharsets UTF 8   final String hex   BaseEncoding base16   lowerCase   encode bytes     Now hex is  48656c6c6f20776f726c64

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Ok so there are a bunch of ways to do this  but if you decide to use a library I would suggest poking about in your project to see if something has been implemented in a library that is already part of your project before adding a new library just to do this   For example if you don t already have      org apache commons codec binary Hex   maybe you do have        org apache xerces impl dv util HexBin

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We don t need to use any external library or to write code based on loops and constants  Is enough just this   byte   theValue         String hexaString   new BigInteger 1  theValue  toString 16

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public static String toHexString byte   bytes         StringBuilder sb   new StringBuilder         if  bytes    null           for  byte b bytes                 final String hexString   Integer toHexString b  amp  0xff                if hexString length    1                  sb append  0                 sb append hexString     append                        return sb toString      toUpperCase

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Simplest solution  no external libs  no digits constants   public static String byteArrayToHex byte   a       StringBuilder sb   new StringBuilder a length   2      for byte b  a        sb append String format   02x   b       return sb toString

[java] How to convert a byte array to a hex string in Java?

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