CODEWITHSUNDEEP
javaiozip
Dumas45
Dumas45

Reputation: 521

java ZipOutputStream doesn't compress

I am trying to output data through ZipOutputStream, but the resulting file is not compressed. This is under Windows 7. Here is an example:

import java.io.*;
import java.nio.file.*;
import java.util.Random;
import java.util.zip.*;

public class Testy {
    public static void main(String[] args) {
        byte[] data = new byte[100];
        Random rnd = new Random(System.currentTimeMillis());
        try {
            BufferedOutputStream out = new BufferedOutputStream(Files.newOutputStream(
                    Paths.get("record.zip"), StandardOpenOption.CREATE, StandardOpenOption.APPEND), 200000);
            ZipOutputStream zout = new ZipOutputStream(out);
            zout.setLevel(4);

            zout.putNextEntry(new ZipEntry("record.dat"));
            for (int i = 0; i < 10000; i++) {
                rnd.nextBytes(data);
                zout.write(data, 0, data.length);
                Thread.sleep(1L);
            }
            zout.closeEntry();
            zout.finish();
            zout.close();
        } catch (IOException | InterruptedException e) {
            e.printStackTrace(System.out);
        }
    }
}

thanks for any help

Upvotes: 1

Views: 619

Answers (1)

Joni
Joni

Reputation: 111219

Compression works by encoding repeated and predictable patterns in the input with shorter byte sequences. A completely random input, like you have here, has no predictable patterns, and cannot be compressed. The same would happen if you compressed a file that had already been compressed.

Try generating random upper case characters, random English words, or a random DNA sequence (letters A C T G) instead of random bytes, and you will see how well they are compressed.

Upvotes: 3

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