How programming block in java?

How programming block in java?

I try copy data from file to file but each 32 bytes for one translate also
the copy shuld be integer number translate like the following
byte[] block = new byte[32];
FileInputStream fis = new FileInputStream(clearmsg);
FileOutputStream fcs = new FileOutputStream(ciphermsg);
int i;
while ((i = fis.read(block)) != -1) {
BigInteger M2 = new BigInteger(block);
byte[] block2=new byte[32] ;
block2 = M2.toString().getBytes();
fos.write(block2, 0, i);
}
fos.close();
but when run this part and take M2.bitLength() it give me 255 bits Why any
suggest