How to get the length of the original array according to the compressed byte array of GZIP?

Question

Before decompressing the array compressed by GZIP, I would like to know the length of the original array so as to apply for a suitable buffer array.Like "1024" in the following code.Thanks!

        byte[] buffer = new byte[1024];
        ByteArrayOutputStream out = new ByteArrayOutputStream(1024);
        try (ByteArrayInputStream bin = new ByteArrayInputStream(localByteBuf);
             GZIPInputStream gis = new GZIPInputStream(bin)) {
            int len;
            while ((len = gis.read(buffer)) > 0) {
                out.write(buffer, 0, len);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }

Answer 1

ByteArrayOutputStream will take care of growing the internal byte[] array. As per the class javadoc:

This class implements an output stream in which the data is written into a byte array. The buffer automatically grows as data is written to it.

You most likely want to copy the stream using InputStream.transferTo() to make the code more readable:

ByteArrayOutputStream out = new ByteArrayOutputStream(); // default 32 size
GZIPInputStream in = new GZIPInputStream(
        new ByteArrayInputStream(localByteBuf)));
in.transferTo(out);