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I have a GZIPInputStream that I constructed from another ByteArrayInputStream. I want to know the original (uncompressed) length for the gzip data. Although I can read to the end of the GZIPInputStream, then count the number, it will cost much time and waste CPU. I would like to know the size before read it.
Is there a similiar method like ZipEntry.getSize() for GZIPInputStream:
public long getSize ()
Since: API Level 1
Gets the uncompressed size of this ZipEntry.
886
For each file, compute the ratio in sizes between gzip -c "$f" | wc -c and wc -c "$f" The average of those ratios is an approximation of the compression you should expect for a similar JS file.
To use the Java GZIPInputStream you must first create a GZIPInputStream instance. Here is an example of creating a GZIPInputStream instance: InputStream fileInputStream = new FileInputStream("myfile. zip"); GZIPInputStream gzipInputStream = new GZIPInputStream(fileInputStream);
GZIPInputStream(InputStream in) Creates a new input stream with a default buffer size. GZIPInputStream(InputStream in, int size) Creates a new input stream with the specified buffer size.
A more compact version of the calculation based on the 4 tail bytes (avoids using a byte buffer, calls Integer.reverseBytes to reverse the byte order of read bytes).
private static long getUncompressedSize(Path inputPath) throws IOException
{
long size = -1;
try (RandomAccessFile fp = new RandomAccessFile(inputPath.toFile(), "r")) {
fp.seek(fp.length() - Integer.BYTES);
int n = fp.readInt();
size = Integer.toUnsignedLong(Integer.reverseBytes(n));
}
return size;
}
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