Easy way to concatenate two byte arrays

Question

What is the easy way to concatenate two byte arrays   Say   byte a    byte b      How do I concatenate two byte arrays and store it in another byte array

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The most elegant way to do this is with a ByteArrayOutputStream   byte a    byte b     ByteArrayOutputStream outputStream   new ByteArrayOutputStream     outputStream write  a    outputStream write  b     byte c     outputStream toByteArray

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If you prefer ByteBuffer like  kalefranz  there is always the posibility to concatenate two byte    or even more  in one line  like this   byte   c   ByteBuffer allocate a length b length  put a  put b  array

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For two or multiple arrays  this simple and clean utility method can be used          Append the given byte arrays to one big array        param arrays The arrays to append     return The complete array containing the appended data     public static final byte   append final byte      arrays        final ByteArrayOutputStream out   new ByteArrayOutputStream        if  arrays    null            for  final byte   array   arrays                if  array    null                    out write array  0  array length                                     return out toByteArray

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This is my way to do it   public static byte   concatByteArrays byte      inputs        int i   inputs length - 1  len   0      for    i  gt   0  i--            len    inputs i  length            byte   r   new byte len       for  i   inputs length - 1  i  gt   0  i--            System arraycopy inputs i   0  r  len -  inputs i  length  inputs i  length             return r      Features    Use varargs       to be called with any number of byte    Use System arraycopy   that is implemented with machine specific native code  to ensure high speed operation  Create a new byte   with the exact size that is need it  Allocate little less int variables by reusing the i and len variables  Faster comparison with constants    Keep in mind   The better way to do this  is by copy the  Jonathan code  The issue comes from the native variable arrays  because Java create new variables when this data type is passed to another function

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byte   result   new byte a length   b length      copy a to result System arraycopy a  0  result  0  a length      copy b to result System arraycopy b  0  result  a length  b length

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Merge two PDF byte arrays If you are merging two byte arrays which contain PDF  this logic will not work  We need to use a third-party tool like PDFbox from Apache  ByteArrayOutputStream byteArrayOutputStream   new ByteArrayOutputStream    mergePdf addSource new ByteArrayInputStream a    mergePdf addSource new ByteArrayInputStream b    mergePdf setDestinationStream byteArrayOutputStream   mergePdf mergeDocuments    c   byteArrayOutputStream toByteArray

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If you don t want to mess with arrays  sizes  just use the magic of string concatenation   byte   c    new String a   l1     new String b   l1    getBytes  l1      Or define somewhere in your code     concatenation charset static final java nio charset Charset cch   java nio charset StandardCharsets ISO 8859 1    and use  byte   c    new String a  cch    new String b  cch   getBytes cch     This  of course  also works with more than two string concatenations using the   addition operator     Both  l1  and ISO 8859 1 indicate the Western Latin 1 character set that encodes each character as a single byte  As no multi-byte translations are performed the characters in the string will have the same values as the bytes  except that they will always be interpreted as positive values  as char is unsigned   At least for the Oracle provided runtime  any byte will therefore be correctly  decoded  and then  encoded  again   Beware that strings do expand the byte array considerately  requiring additional memory  Strings may also be interned and will therefore not easy be removed  Strings are also immutable  so the values inside them cannot be destroyed  You should therefore not concatenate sensitive arrays this way nor should you use this method for larger byte arrays  Giving a clear indication of what you are doing would also be required  as this method of array concatenation is not a common solution

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You can use third party libraries for Clean Code like Apache Commons Lang and use it like   byte   bytes   ArrayUtils addAll a  b

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Another possibility is using java nio ByteBuffer   Something like  ByteBuffer bb   ByteBuffer allocate a length   b length   c length   bb put a   bb put b   bb put c   byte   result   bb array        or using method chaining   byte   result   ByteBuffer          allocate a length   b length   c length           put a  put b  put c           array      Note that the array must be appropriately sized to start with  so the allocation line is required  as array   simply returns the backing array  without taking the offset  position or limit into account

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Here s a nice solution using Guava s com google common primitives Bytes   byte   c   Bytes concat a  b     The great thing about this method is that it has a varargs signature   public static byte   concat byte      arrays    which means that you can concatenate an arbitrary number of arrays in a single method call

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Another way is to use a utility function  you could make this a static method of a generic utility class if you like    byte   concat byte     arrays           Determine the length of the result array     int totalLength   0      for  int i   0  i  lt  arrays length  i                  totalLength    arrays i  length                create the result array     byte   result   new byte totalLength           copy the source arrays into the result array     int currentIndex   0      for  int i   0  i  lt  arrays length  i                  System arraycopy arrays i   0  result  currentIndex  arrays i  length           currentIndex    arrays i  length             return result      Invoke like so   byte   a  byte   b  byte   result   concat a  b     It will also work for concatenating 3  4  5 arrays  etc   Doing it this way gives you the advantage of fast arraycopy code which is also very easy to read and maintain

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Most straightforward   byte   c   new byte a length   b length   System arraycopy a  0  c  0  a length   System arraycopy b  0  c  a length  b length

[java] Easy way to concatenate two byte arrays

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