How to zip an array in memory?

Question

I have a byte array, and I intend to zip it into another array. How can I do it without having to create a temporary ZIP file to store the zipped contents?
Here is the small prototype code have I developed to try the idea (ZipTest.java):
import java.util.zip.*;
import java.io.*;
public class ZipTest{
     static public void main(String[] args)
      throws IOException{
          //testing stream without zipping first
          ByteArrayOutputStream stream = new ByteArrayOutputStream();
          byte[] b = {1, 2, 3, 4, 5};
          stream.write(b, 0, b.length);
          byte[] b2 = stream.toByteArray();
          for(int i = 0; i <= b2.length - 1; i += 1)
               System.out.println(b2[i] + "");
          //the previous code piece works well and generates the proper output
          //now, testing stream with zipping
          stream = new ByteArrayOutputStream();
          ZipOutputStream zip = new ZipOutputStream(stream);
          zip.write(b, 0, b.length); // the exception is generated here
          b2 = stream.toByteArray();
          for(int i = 0; i <= b2.length - 1; i += 1)
               System.out.println(b2[i] + "");
}The output is the following:
1
2
3
4
5
Exception in thread "main" java.util.zip.ZipException: no current ZIP entry
        at java.util.zip.ZipOutputStream.write(Unknown Source)
        at ZipTest.main(ZipTest.java:19)What should I do to solve this problem?

Answer 1

Try
public class ZipTest {
    public static void main(String[] args) throws IOException {
        //testing stream without zipping first
        ByteArrayOutputStream stream = new ByteArrayOutputStream();
        byte[] b = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
        stream.write(b);
        stream.close();
        byte[] b2 = stream.toByteArray();
        System.out.println("Uncompressed len=" + b2.length + ' ' + Arrays.toString(b2));
        //the previous code piece works well and generates the proper output
        //now, testing stream with zipping
        ByteArrayOutputStream stream2 = new ByteArrayOutputStream();
        DeflaterOutputStream zip = new DeflaterOutputStream(stream2);
        zip.write(b);
        zip.close();
        byte[] b3 = stream2.toByteArray();
        System.out.println("Compressed len=" + b3.length + ' ' + Arrays.toString(b3));
}You will note that for trivial messages the header adds more than the compression saves.