Question

When using the deflate-method of java.util.zip.Deflater, a byte[] has to be supplied as the argument, how big should that byte[] be initialized to? I’ve read there’s no guarantee the compressed data will even be smaller that the uncompressed data. Is there a certain % of the input I should go with?
Currently I make it twice as big as the input

Answer 1

After calling deflate, call finished to see if it still has more to output. eg:

byte[] buffer = new byte[BUFFER_SIZE];
while (!deflater.finished()) {
  int n = deflater.deflate(buffer);
  // deal with the n bytes in out here
}

If you just want to collect all of the bytes in-memory you can use a ByteArrayOutputStream. eg:

byte[] buffer = new byte[BUFFER_SIZE];
ByteArrayOutputStream baos = new ByteArrayOutputStream();
while (!deflater.finished()) {
  int n = deflater.deflate(buffer);
  baos.write(buffer, 0, n);
}
return baos.toByteArray();