Appending a byte to the end of another byte

Question

I have two byte   arrays which are of unknown length and I simply want to append one to the end of the other  i e    byte   ciphertext   blah  byte   mac   blah  byte   out   ciphertext   mac    I have tried using arraycopy   but can t seem to get it to work

User · Answer

First you need to allocate an array of the combined length  then use arraycopy to fill it from both sources   byte   ciphertext   blah  byte   mac   blah  byte   out   new byte ciphertext length   mac length     System arraycopy ciphertext  0  out  0  ciphertext length   System arraycopy mac  0  out  ciphertext length  mac length

User · Answer

You need to declare out as a byte array with a length equal to the lengths of ciphertext and mac added together  and then copy ciphertext over the beginning of out and mac over the end  using arraycopy   byte   concatenateByteArrays byte   a  byte   b        byte   result   new byte a length   b length        System arraycopy a  0  result  0  a length        System arraycopy b  0  result  a length  b length        return result

User · Answer

The other provided solutions are great when you want to add only 2 byte arrays  but if you want to keep appending several byte   chunks to make a single   byte   readBytes      Your byte array        for eg  readBytes    TestBytes  getBytes     ByteArrayBuffer mReadBuffer   new ByteArrayBuffer 0        Instead of 0  if you know the count of expected number of bytes  nice to input here  mReadBuffer append readBytes  0  readBytes length      this copies all bytes from readBytes byte array into mReadBuffer    Any new entry of readBytes  you can just append here by repeating the same call      Finally  if you want the result into byte   form  byte   result   mReadBuffer buffer

User · Answer

Perhaps the easiest way   ByteArrayOutputStream output   new ByteArrayOutputStream     output write ciphertext   output write mac    byte   out   output toByteArray

User · Answer

Using System arraycopy    something like the following should work      create a destination array that is the size of the two arrays byte   destination   new byte ciphertext length   mac length       copy ciphertext into start of destination  from pos 0  copy ciphertext length bytes  System arraycopy ciphertext  0  destination  0  ciphertext length       copy mac into end of destination  from pos ciphertext length  copy mac length bytes  System arraycopy mac  0  destination  ciphertext length  mac length

User · Answer

I wrote the following procedure for concatenation of several array     static public byte   concat byte      bufs        if  bufs length    0          return null      if  bufs length    1          return bufs 0       for  int i   0  i  lt  bufs length - 1  i              byte   res   Arrays copyOf bufs i   bufs i  length bufs i   1  length           System arraycopy bufs i   1   0  res  bufs i  length  bufs i   1  length           bufs i   1    res            return bufs bufs length - 1       It uses Arrays copyOf

[java] Appending a byte[] to the end of another byte[]

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