my question might not be entirely related to Java but I'm currently seeking a method to combine several compressed (gzipped) textfiles without the requirement to recompress them manually. Lets say I have 4 files, all text that is compressed using gzip and want to compress these into one single *.gz file without de + recompressing them. My current method is to open an InputStream and parse the file linewise, storing in a GZIPoutputstream, which works but isn't very fast.... I could of course also call
zcat file1 file2 file3 | gzip -c > output_all_four.gz
This would work, too but isn't really fast either.
My idea would be to copy the inputstream and write it to outputstream directly without "parsing" the stream, as I don't need to manipulate anything actually. Is something like this possible?
Find below a simple solution in Java (it does the same as my cat ... example). Any kind of buffering the input/output has been omitted to keep the code slim.
public class ConcatFiles {
public static void main(String[] args) throws IOException {
// concatenate the single gzip files to one gzip file
try (InputStream isOne = new FileInputStream("file1.gz");
InputStream isTwo = new FileInputStream("file2.gz");
InputStream isThree = new FileInputStream("file3.gz");
SequenceInputStream sis = new SequenceInputStream(new SequenceInputStream(isOne, isTwo), isThree);
OutputStream bos = new FileOutputStream("output_all_three.gz")) {
byte[] buffer = new byte[8192];
int intsRead;
while ((intsRead = sis.read(buffer)) != -1) {
bos.write(buffer, 0, intsRead);
}
bos.flush();
}
// ungezip the single gzip file, the output contains the
// concatenated input of the single uncompressed files
try (GZIPInputStream gzipis = new GZIPInputStream(new FileInputStream("output_all_three.gz"));
OutputStream bos = new FileOutputStream("output_all_three")) {
byte[] buffer = new byte[8192];
int intsRead;
while ((intsRead = gzipis.read(buffer)) != -1) {
bos.write(buffer, 0, intsRead);
}
bos.flush();
}
}
}